title stringlengths 0 1.13k | abstract stringlengths 1 15.7k | PMID int64 22 36.5M |
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Simplex optimization of ion-pair reversed-phase high performance liquid chromatographic analysis of some heavy metals. | The sequential simplex algorithm was used to optimize the ion-pair reversed phase high performance liquid chromatographic (IP-RPHPLC) analysis of 4-(2-pyridylazo)resorcinol (PAR) chelates of Co(II), Ni(II) and Cr(III). A chromatographic response function (CRF) which included the number of peaks, the resolution between adjacent peaks, a specified analysis time, and the individual retention times relative to a minimum retention time, was calculated to evaluate the quality of the individual chromatograms. The optimum conditions for the three experimental parameters were 28.6% acetonitrile in the mobile phase, 3.0 mmol l(-1) concentration of acetate buffer at pH 6.0, and 5.2 mmol l(-1) tetrabutylammonium bromide (TBABr). Optimum conditions were achieved in only 19 experiments. The order of elution was Co(II)PAR, Cr(III)PAR and Ni(II)PAR, respectively, with an analysis time of 15 min. | 18,968,540 |
Determination of trace amounts of germanium by flow injection hydride generation atomic fluorescence spectrometry with on-line coprecipitation. | A method for the determination of trace amounts of germanium by hydride generation atomic fluorescence spectrometry (HG-AFS) associated on-line with flow injection (FI) coprecipitation preconcentration was described. The samples, each spiked with Ni(2+) (500 mugml(-1)), were introduced into the FI system using time-based injection, and mixed with a NaOH solution (50 gl(-1)). Germanium was preconcentrated by coprecipitation with the generated nickel hydroxide precipitate. The precipitate is subsequently eluted with 20% (v/v) phosphate acid solution and directed into the HG-AFS system. This method is simple and rapid. The detection limit (3sigma) was 0.11 mugl(-1) and the relative standard deviation was 5.6% (n=11) at the 10 mugl(-1) level. | 18,968,547 |
Electrochemical sensor for detection of unmodified nucleic acids. | We have developed a nucleic acid (NA) sensor based on mediated electrochemical oxidation of guanine residues. In this method, oligonucleotide probes are bound to a tin-doped indium oxide (ITO) electrode through a self-assembled phosphonate monolayer. The end carboxyl moiety of the monolayer is activated with carbodiimide and reacted with the amine group of a C6 alkyl linker which has been added to the 5'-end of the oligonucleotide probe. Upon hybridization of the complementary target NA, the hybrid is detected using a redox-active mediator, tris(2,2'-bipyridyl) ruthenium(II). We speculate that the monolayer does not impede electron-transfer since it contains many defect sites when assembled on a polycrystalline ITO surface. These defect sites are accessible to the mediator, but not to NA or proteins. The electrocatalytic current was a linear function of the amount of guanine bound at the electrode surface, with a detection limit of 120 amoles of guanine cm(-2) at 0.28 cm(2) ITO electrodes. | 18,968,560 |
Interaction of DNA with echinomycin at the mercury electrode surface as detected by impedance and chronopotentiometric measurements. | The capacitance measurement (dependence of the differential capacitance C of the electrode double layer on potential E, C-E curves), electrochemical impedance spectroscopy (frequency response of the impedance Z of the electrode double layer-EIS) and constant current chronopotentiometry (dependence of dt/dE on potential at constant current, chronopotentiometric stripping analysis-CPSA) have been used for electrochemical study of echinomycin and its interaction with single-stranded (ss) and double-stranded (ds) DNA at the hanging mercury drop electrode (HMDE). The capacitance measurement showed that echinomycin gives a pseudocapacitance redox peak strongly dependent on the a.c. voltage frequency at the potential of -0.53 V. This peak is observed with dsDNA-echinomycin complex as well, but not with ssDNA treated by echinomycin. Similar results were obtained using CPSA measurements. Thus capacitance measurements and CPSA can distinguish with the aid of the bis-intercalator echinomycin the single-stranded and double helical form of DNA adsorbed at the mercury electrode surface. Impedance measurement in connection with adsorptive transfer technique can find the differences between ssDNA and dsDNA, which promise to use this technique for detection of dsDNA in hybridisation reactions. | 18,968,569 |
Superheated water eluent capillary liquid chromatography. | A capillary scale reverse phase liquid chromatography (LC) system using a super hot water eluent is described. The system, constructed in-house from readily available components, has been shown to operate at temperatures as high as 370 degrees C and pressures in excess of 10 000 psi. The capability of the system is demonstrated with the separation of a mixture of polar and non-polar benzene derivatives on polybutadiene and elemental carbon modified zirconia packings with or without temperature gradients. Six benzene derivatives can be separated in approximately 2 min. | 18,968,577 |
Aromatic compounds in molecular phase of Baltic amber-synchronous luminescence analysis. | Synchronous luminescence analysis was performed in order to identify aromatic compounds in solvent extracts of Baltic amber. The investigated extracts were obtained, for comparisons, as products of extraction by various techniques and solvents. Methylene chloride and ethanol were applied independently for extraction at the ambient temperature (conservative extraction), as well as at the temperature of solvent boiling (extraction in Soxhlet apparatus). Ethanol, as the solvent, was also used for extraction in an ultrasonic bath and for the decoction process. The extraction, by techniques mentioned, of the analysed amber has resulted in products generally containing the same groups of aromatics: mainly naphthalenes, phenanthrenes and anthracenes. Among phenanthrenes, in all samples the retene was also identified, being one of the characteristic links of the diagenetic chain of chemical transformations of vegetal precursors. The identification of a series of individual compounds made, using the synchronous luminescence technique, was verified by the record of conventional emission and excitation spectra. Presented identified compounds were also confirmed by the results of GC-MS analysis. The luminescence analysis was also performed comparatively for fossil resin from Galicia, Spain (Cretaceous) older than Baltic amber (Tertiary, Eocene). The obtained preliminary results of synchronous luminescence analysis suggest the possibility of diversification in this manner of fossil resins of various ages by characterisation of aromatisation degree and alkyl substitution of aromatic rings. It is since well known that aromatisation progress is an indicator of a natural process of maturation of fossil organic matter. However, a greater number of samples should be taken to further testify to the investigations. | 18,968,585 |
Determination of urinary lead, cadmium and nickel in steel production workers. | The determination of toxic metals in urine is an important clinical screening procedure. In this study, the aim of our investigation was to determine the concentrations of Pb, Cd, and Ni in urine samples under routine clinical laboratory conditions. To assess the reliability of these methods, critical factors such as detection limit(s), calibration range(s), cost, accuracy and precision were studied. The method was employed for the quantitative determination of lead, cadmium and nickel in urine samples from steel production and quality control (QC) workers and healthy unexposed controls. After pre-treatment with acids, the samples were digested via a microwave oven and the samples were determined by a graphite furnace atomic absorption spectrometry (GFAAS). Quality control for these procedures was established with the concurrent analysis of Standard Trace Metals 7879 Level II and NIST SRM 2670 (Toxic Elements in Freeze Dried Urine). The results indicate that urinary lead, cadmium and nickel levels of the exposed workers are significantly higher those of the controls. The possible connection of these elements with the etiology of disease is discussed. The results also show the need for immediate improvements in workplace ventilation and industrial hygiene practices. | 18,968,591 |
Synthesis of polyacrylaminoimidazole chelating fiber and properties of concentration and separation of trace Au, Hg and Pd from samples. | A novel polyacrylaminoimidazole chelating fiber is synthesized simply and rapidly from nitrilon (an acrylonitrile-based synthetic fiber) and used for the preconcentration and separation of trace Au(III), Hg(II) and Pd(IV) ions from solution samples. The analyzed ions can be quantitatively concentrated by the fiber up to a flow rate of 15.0 mlmin(-1) at pH 3 and can also be desorbed with 15 ml of 4 M HCl+3% thiourea from the fiber column, with recoveries of 96.5-100%. The chelating fiber is reused ten times; the recoveries of these ions are still over 92%, and 100-1000 times of excess of Fe(III), Al(III), Ca(II), Mg(II), Ni(II), Mn(II), Cu(II), Zn(II) and Cd(II) causes no interference in the determination of these ions by inductively coupled plasma atomic emission spectrometry. The capacities of the fiber for the analytes are in the range of 1.56-2.92 mmolg(-1). The results show that the relative standard deviations for the determination of 50.0 ngml(-1) each of Au(III), Hg(IV) and Pd(IV) are in the range of 0.7-2.1%. The recoveries of a standard added in real solution samples are between 97 and 99%, and the concentration of each ion in powder sample detected by the method is in good agreement with the certified value. | 18,968,608 |
Continuous flow analysis of iron in zinc electrowinning electrolyte using an iron chalcogenide glass ion-selective electrode Part I. Synthetic media. | It is shown that the iron(III) chalcogenide glass membrane ion-selective electrode (ISE) can be calibrated in continuous flow analysis (CFA) using acidified iron(III) nitrate standards, yielding a 60+/-3 mV per decade change in activity of Fe(3+) response in the range 10(-7)-10(-2) M total iron(III). Extended ageing of the iron(III) ISE in 2 M zinc(II) sulphate did not alter the potentiometric response characteristics of the electrode. Furthermore, electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy in the presence and absence of zinc(II) sulphate failed to detect a zinc(II) interference on the iron(III) ISE. CFA/ISE determined activities of Fe(3+) in synthetic zinc electrolyte containing 2x10(-3)-2x10(-1) M total iron(III) yielded results falling within +/-0.2logaFe(3+) unit of the corresponding iron speciation data calculated using the minteqa2 program. | 18,968,611 |
Use of constrained DET probe for a high-resolution determination of metals and anions distribution in the sediment pore water. | The constrained DET (diffusive equilibrium in thin films) probe filled with agarose gel was successfully used for measuring depth profiles of metals and anions in estuarine sediments at high-resolution (mm). The agarose gel was tested for equilibration times and recoveries. For manganese (10 mg l(-1)), the equilibration time between an aqueous solution and the agarose gel was reached after 60 min. In the presence of humic acids it was five times longer. As a consequence, for field applications a deployment time of 5-24 h was applied. The subsequent elution of manganese into nitric acid was completed in less than 10 min even without mixing. For agarose gel in contact with solutions of 10 mg l(-1) ions (cadmium, copper and manganese, bromide, chloride, nitrate and sulfate), recoveries obtained were close to 100%. DET probes were applied in test laboratory sediment and in real sediment in the Authie (France) estuary. Depth profiles for 19 elements (Ag, As, Ba, Bi, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, Se, Sr, Tl, V, and Zn) and four anions (bromide, chloride, nitrate and sulfate) were established for the test laboratory sediment. In the real sediment, the pore water concentrations of iron and manganese using gel probes were comparable with those obtained by a conventional method (box core-anoxic slicing followed by centrifugation). | 18,968,614 |
A highly stable biosensor for phenols prepared by immobilizing polyphenol oxidase into polyaniline-polyacrylonitrile composite matrix. | A novel biosensor for phenols was constructed by immobilizing polyphenol oxidase (PPO) into polyaniline-polyacrylonitrile composite matrix. The sensing film was prepared by electropolymerization of aniline into polyacrylonitrile (PAN)-coated platinum electrode in the presence of PPO. The scanning electron micrographs (SEM) showed that PAN had microporous structure and polyaniline and the enzyme could co-intercalated into PAN matrix. The obtained biosensor exhibited high sensitivity and excellent stability, which had no apparent loss of activity after 100 consecutive measurements and intermittent usage for 8 months with storage in a phosphate buffer at 4 degrees C. The construction and operational conditions of the enzyme electrode were optimized. The sensitivities of the enzyme electrode for phenol, p-cresol, m-cresol and catechol were 0.96, 1.38, 1.5 and 2.03 AM(-1)cm(-2), respectively. | 18,968,629 |
The application of the chromatomembrane cell for the absorptive sampling of nitrogen dioxide followed by continuous determination of nitrite using a micro-flow injection system. | A simple and rapid procedure for NO(2) determination in air was developed by coupling the chromatomembrane method with a micro-FIA system. A three-hole chromatomembrane cell was successfully applied to on-line preconcentration of atmospheric NO(2) in a solution of 2 g l(-1) triethanolamine (TEA) as an aqueous absorbing solution. The lowest volume of an air sample necessary for the measurement was 5, and 0.02 ml portions of the solution containing the absorbed NO(2) (NO(2)(-) and NO(3)(-)) were supplied to a micro-FIA system being the succeeding component of the proposed analyzer. The amounts of NO(2)(-) in the absorbing solution were measured by a diazotization-coupling reaction with sulfanilamide and N-(1-naphthyl) ethylenediamine, and referred to the concentration of NO(2) in the air sample. The NO(2) content of indoor air was determined to be 43+/-1 ppb using 20 ml of air, and the R.S.D. was +/-1.89%. | 18,968,636 |
Amperometric sensor for glucose and hypoxanthine based on a PdIrO(2) modified electrode by a co-crosslinking bienzymic system. | A glassy carbon electrode (GCE) modified with Pd/IrO(2) provides excellent electrocatalytic oxidation of hydrogen peroxide. Glucose oxidase (GOD) and xanthine oxidase (XOD) were co-immobilized on the modified electrode with a thin film Nafion coated on the enzyme layer to form a glucose (Glu)/hypoxanthine (Hx) sensor, without interference from electroactive species such as ascorbic acid (AA) and uric acid (UA). Its response was evaluated with respect to the enzyme amount on the electrode, pH and temperature of the electrolyte. The prepared bienzymic biosensor, used as the detector of HPLC gave a detection limit of 1.0x10(-6) mol l(-1) Glu and 2.0x10(-7) mol l(-1) Hx (Hx) with a linear concentration range of 5.0x10(-6)-2.5x10(-3) mol l(-1) and 1.0x10(-6)-5.0x10(-4) mol l(-1), respectively. Coupled with microdialysis, it was used to monitor the concentrations of Glu and Hx in rat brain. | 18,968,637 |
Combined cation-exchange and extraction chromatography for the concomitant separation of Zr, Hf, Th, and the Lanthanides from geological materials. | A new method was developed, aiming to overcome the iron and titanium interferences which severely limit the applications of a recently introduced extraction chromatography material, referred to as RE resin (formerly, RE Spec), to the analysis of geological samples. The separation scheme is based on the combined use, in tandem columns, of the conventional AG50WX4 cation-exchange resin and the RE extraction chromatography material, without any intervening evaporation step. The Lanthanides are recovered quantitatively, while recoveries for Zr, Hf and Th range from 94 to 98%. These three elements are determined using the isotope dilution method, thereby alleviating the need for a yield correction. Compared with conventional methods based on cation-exchange, this combined scheme offers a greater multi-element capability, significant miniaturisation, acid wastes reduction, and a higher degree of purity of the separated analytes with regard to unwanted elements such as Ba and residual Ca and Al. This concomitant isolation of 17 trace elements of great interest in the Earth and Environmental Sciences, achieved with excellent recoveries and satisfactory blank levels, can be used prior to high precision analysis of ultra-trace elements in geological samples by ICP-Mass Spectrometry. | 18,968,640 |
Voltammetric behaviour and trace determination of copper at a mercury-free screen-printed carbon electrode. | Screen-printed carbon electrodes (SPCEs), without chemical modification, have been investigated as disposable sensors for the measurement of trace levels of Cu(2+). Cyclic voltammetry was employed to elucidate the electrochemical behaviour of Cu(2+) at these electrodes in a variety of supporting electrolytes. For all of the electrolytes studied the anodic peaks, obtained on the reverse scans, showed that the Cu(2+) had been deposited as a thin layer on the surface of the SPCE. The anodic peak of greatest magnitude was obtained in 0.1 M malonic acid. The possibility of determining Cu(2+) at trace levels using this medium was examined by differential pulse anodic stripping voltammetry (DPASV). The effect of Bi(3+), Cd(2+), Fe(3+), Hg(2)(2+), Pb(2+), Sb(3+) and Zn(2+) on the Cu stripping peak was examined and under the conditions employed, only Hg(2)(2+) was found to significantly effect the response gained. The sensors were evaluated by carrying out Cu(2+) determinations on spiked and unspiked serum and water samples. The mean recovery was found in all cases to be >90% and the performance characteristics indicated the method holds promise for trace Cu(2+) levels by employment of Hg-free SPCEs using DPASV. | 18,968,656 |
Sample pre-treatment methods for the trace elements determination in seafood products by atomic absorption spectrometry. | Different sample pre-treatments for seafood products have been compared with determine trace elements (As, Cd, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Se and Zn) by flame atomic absorption spectrometry (FAAS) and electrothermal atomic absorption spectrometry (ETAAS). Classic pre-treatments as microwave assisted-acid digestion and the slurry sampling technique were compared with new procedures such as microwave energy or ultrasound energy assisted-acid leaching process and enzymatic hydrolysis methodologies based on the use of pronase E. The methods were applied to DORM-1 and DOLT-1 reference materials with certified contents for the studied elements. The Student-Newman-Keuls (SNK) method was used to compare with element concentration means obtained with each sample pre-treatment and also the certified concentration means in both reference materials. Multivariate techniques such as principal components analysis (PCA) was also applied to comparative purposes. | 18,968,702 |
Carbon-13 NMR spectroscopic studies on chemically modified and unmodified synthetic and natural humic acids. | Carbon-13 cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy ((13)C-CP/MAS-NMR) was applied to study the chemical modification process of humic acids (HA) with diazomethane and the subsequent alkaline hydrolysis of the methylated HA. This modification process results in HA with selectively blocked phenolic OH groups, which can be used for metal ion binding studies with humic substances. Different chemically modified and unmodified natural and synthetic HA with carbon-13 of natural abundance were investigated. In addition, carbon-13 labeled modified synthetic HA, that were synthesized with [(13)C]diazomethane as methylation reagent, were studied to confirm the assumed modification process and to determine the type of functional groups that have the highest affinity for methylation with diazomethane. The results of the NMR studies with carbon-13 labeled modified HA show that predominantly carboxyl and phenolic OH groups are methylated with diazomethane resulting in methyl ester and methyl ether groups, respectively. Due to the alkaline treatment of the methylated HA, the methyl esters of carboxyl groups are hydrolyzed, whereas methyl ethers of phenolic OH groups remain unchanged, which results in modified HA with blocked phenolic OH groups. From the spectra of the modified and unmodified HA with carbon-13 of natural abundance it can be concluded that the applied preparative modification procedure causes only the desired structural changes in HA. | 18,968,705 |
Design of a composite amperometric enzyme electrode for the control of the benzoic acid content in food. | A graphite-Teflon-tyrosinase composite biosensor for the determination of benzoic acid in foodstuffs is reported. The biosensor functioning is based on the inhibition effect of benzoic acid on the biocatalytic activity of the enzyme in a reversed micelle working medium formed with ethyl acetate as the continuous phase, a 0.05 moll(-1) phosphate buffer solution of pH 7.4 (5%) as the aqueous dispersed phase, and 0.10 moll(-1) dioctyl sulfosuccinate (AOT) as the emulsifying agent. A potential value of -0.10 V, and a constant enzyme-substrate (phenol) concentration of 2.0x10(-4) moll(-1) were selected to carry out the amperometric inhibition measurements. The tyrosinase inhibition process by benzoic acid is reversible and of the competitive type, with an apparent inhibition constant of 0.016 mmoll(-1). The composite bioelectrodes allow the regeneration of the electrode surface by polishing and exhibit long-term operation and stability. A limit of detection of 9.0x10(-7) moll(-1) benzoic acid was obtained. An interference study from other substances which can be found in foodstuffs together with benzoic acid was performed. Taking advantage of the capabilities of reversed micelles as universal solubilization media, the composite tyrosinase electrode was used for the determination of benzoic acid in two different kind of samples: mayonnaise sauce, which is a highly hydrophobic matrix, and Cola soft drinks, a hydrophilic matrix for which practically no sample treatment is necessary. | 18,968,725 |
Electrochemical measurement and speciation of inorganic arsenic in groundwater of Bangladesh. | The presence of arsenic in groundwater above the maximum permissible limit of 50 mug l(-1) has threatened the health of more than 50 million people in Bangladesh and neighboring India. We report here the development of an inexpensive anodic stripping voltammetric (ASV) technique for routine measurement and speciation of arsenic in groundwater. The measurements are validated by more expensive atomic absorption, atomic emission and other techniques. To understand the present situation in Bangladesh, we measured As(III) in 960 water samples collected from 18 districts. A random distribution of 238 samples was used to measure both As(III) and As(V). The results from the present study indicate that most toxic form of inorganic arsenic, As(III), has the broad range of 30-98%. It shows 60% of the samples have 10 mug l(-1) and 44% of the samples have 50 mug l(-1) or more As(III). The fractional distribution pattern shows significant skew towards high percent occurrence which may indicate a progressive reduction process with a single source or a single mechanism for the formation of As(III). For direct consumption, this is possibly one of the most toxic groundwater known today. Speciation distribution at groundwater pH value shows H(3)AsO(3) is the predominant species including H(2)AsO(4)(-) and H(2)AsO(4)(2-) whose distribution is significantly pH dependent. This is also supported by E(h)-pH measurements. The depth distribution for Kushtia shows most of the As(III) is located within 100-200 ft deep aquifers. Similar fractional distribution of As(III) is found in deeper aquifers and may indicate contamination by leakage from upper aquifer. This study clearly demonstrates the aquifer environment is reductive and conducive to the formation of As(III) species. | 18,968,732 |
Determination of arsenite, arsenate, and monomethylarsonic acid in seawater by ion-exclusion chromatography combined with inductively coupled plasma mass spectrometry using reaction cell and hydride generation techniques. | This paper describes a robust and sensitive method for the determination of arsenic species in seawater by ion-exclusion liquid chromatography (LC) combined with inductively coupled plasma mass spectrometry (ICP-MS) using reaction cell and hydride generation (HG) techniques. A good separation of arsenite, arsenate, and monomethylarsonic acid was achieved using an ion-exclusion column packed with a sulfonated polystyrene resin and a dilute nitric acid at pH 2.0 as the eluent, even when a large volume, i.e. 200 mul, of seawater samples containing a large amount of matrix was repeatedly injected. Separations of the chloride ion due to the matrix and arsenic species were partially performed; however, the extensive peak of ArCl due to high content of Cl(-) in a sample overlapped peaks of the three arsenic species on (75)As measurement by ICP-MS. This ArCl polyatomic interference was efficiently eliminated by collision of ArCl molecules with helium in an octopole reaction cell which was introduced prior to a mass spectrometer. Detection limits of the three arsenic species in a sample containing 2% Cl(-), the concentration of which is comparable to that in a seawater sample, by LC-ICP-MS with the octopole reaction system (ORS), ranged from 21 to 25 pg As ml(-1); these values were three-six times lower than those by LC-ICP-MS without ORS. As another technique for ArCl interference elimination, HG prior to ICP-MS was also successfully used not only to reduce the interference but also to improve the detection limits to 3.4-4.5 pg As ml(-1). The developed LC-ICP-ORS-MS and LC-HG-ICP-MS were validated by analyzing a certified reference material (CRM) of seawater. In addition, no serious decrease in analytical performance of present methods was observed in the experimental periods of half a year for LC-ICP-ORS-MS and 1 year for LC-HG-ICP-MS, respectively. The latter method was successfully applied to characterize seasonal variations of three arsenic species in deep seawater and surface seawater. | 18,968,739 |
Application of FT-IR spectroscopy to the characterisation and classification of wines, brandies and other distilled drinks. | FT-IR spectra were employed for the differentiation and classification of wines and brandies during their ageing process, as well as for the characterisation and differentiation of distilled drinks from several producing countries. The FT-IR spectra have enabled the differentiation of the six scales of ageing of sherry wine. A good linear regression fit (regression coefficient=0.995) has been obtained between ageing scale and the data of the FT-IR spectrum. In the case of Brandy of Jerez, it has been possible to differentiate the three degrees of ageing and to devise a system of classification by means of linear discriminant analysis, with a reliability of 83%. The application of the regression by partial least squares has allowed us to obtain a regression between the degree of ageing and the data of the FT-IR spectrum (correlation coefficient=0.986). Lastly, Spanish, French and South African brandies, as well as cognacs and armagnacs have been characterised, and a complete differentiation of the latter two types from the rest of the samples of distilled drinks has been obtained. | 18,968,750 |
Cyclodextrin enhanced spectrofluorimetric determination of fluoxetine in pharmaceuticals and biological fluids. | The characteristics of host-guest complexation between methyl-beta-cyclodextrin and fluoxetine were investigated by fluorescence spectrometry. A 1:1 stoichiometry of the complex was established and association constant of 4.35x10(-3) M(-1) at 20 degrees C was calculated. A spectrofluorimetric method for the determination of fluoxetine, with a range of application between 40 and 1000 mug l(-1) was developed. Overall least squares regression was used to find the straight line that fitted the experimental data. The detection limit, according to the error propagation theory, was 9.6 mug l(-1) and the detection limit proposed by Clayton was 15.8 mug l(-1). Repeatability and relative standard deviation were also determined according to this theory, with satisfactory results. The method was successfully applied to the determination of fluoxetine in pharmaceuticals and biological fluids. | 18,968,754 |
Creatinine sensitive biosensor based on ISFETs and creatinine deiminase immobilised in BSA membrane. | A creatinine sensitive biosensor based on ion sensitive field-effect transistors (ISFETs) with immobilised creatinine deiminase (CD) is developed. CD is immobilised on the transducer surface by classical cross-linking with bovine serum albumin (BSA) in a glutaraldehyde (GA) vapour. The linear dynamic ranges of biosensors are between 0 and 5 mM creatinine concentration, and the sensor sensitivity depends on the sample buffer concentration. Minimal detection limit for creatinine determination in model solution with 144 mM NaCl and 5% BSA, pH 7.4, is about 10 muM. Biosensor responses are reproducible and stable during continuous work at least for 8 h, and the relative standard deviation of sensor response is approximately 3% (n=48, for creatinine concentrations of 0.2 and 0.6 mM). An investigation about storage stability of creatinine sensitive ENFETs kept in dry at 4-6 degrees C shows that biosensors demonstrate an excellent storage stability for at least 6 months and more. Moreover, creatinine sensitive enzymatic field-effect transistors (ENFETs), demonstrating very good performances, are very selective and specific and well suitable for hemodialysis monitoring. | 18,968,760 |
Determination of lead and cadmium in titanium dioxide by differential pulse anodic stripping voltammetry. | A procedure for the simultaneous determination of lead and cadmium in TiO(2) by differential pulse anodic stripping voltammetry (ASV) has been developed. The key feature of the method is the use of triethanolamine (TEA) to remove titanium interference: TiO(2) undergoes acidic digestion with HF/H(2)SO(4) at atmospheric pressure, TEA is added to the HCl solution of the residue and the solution is analysed using a standard ASV instrumentation, equipped with a hanging mercury drop electrode. The calibration curves for both lead and cadmium are linear up to 50 mugl(-1) of solution, and the detection limits are 1 mugl(-1), corresponding to 1 mugg(-1) of TiO(2). Method reliability was tested by comparing the results with those given by electrothermal atomic absorption spectroscopy. The method has been successfully applied for determination of both contaminants in powdered titanium dioxide (raw materials) and in titanium dioxide-containing cosmetics (sunscreen products). | 18,968,775 |
Measuring the transverse concentration gradient between adjacent laminar flows in a microfluidic device by a laser-based refractive index gradient detector. | A detection scheme that probes the refractive index gradient (RIG) between adjacent laminar flows in microfluidic devices has been developed and evaluated. The behavior of low Reynolds number flows has been well documented and shows that molecular transport (mixing) between adjacent laminar flows occurs by molecular diffusion between the flow boundaries. A diode laser has been used to probe the transverse concentration gradient at a selected position along a microchannel. The concentration gradient is affected by the transverse diffusion from a flow with analyte into a flow initially without analyte. To optimize sensitivity, the RIG is probed at a position in which molecular diffusion across the boundary of the two flows has been minimal, i.e. just after the flow initially without analyte merges with the flow initially containing the analyte at a given concentration. The RIG formed causes the laser beam, impinging orthogonal to the RIG through the microchannel, to be deflected. The angle of deflection is then monitored on a position sensitive detector (PSD). Currently, this detection scheme is demonstrated to provide quantitative detection of sucrose, as a test analyte, with a concentration limit of detection (LOD) of 96 ppm (w/v) or 280 muM, corresponding to 1.3x10(-5) DeltaRI units using 3sigma baseline noise. A dynamic range of 96 ppm to 50% sucrose is obtained. This detection method provides universal detection selectivity for microfluidic analysis systems that are becoming increasingly useful in monitoring chemical systems, particularly for the polymer, pharmaceutical and life sciences fields. For a larger molecular weight analyte with a smaller diffusion coefficient, lower concentration and RI LODs were achieved since detection sensitivity is a function of analyte diffusion. For example, for the polymer poly (ethylene glycol) with a molar mass of 11 840 g mol(-1), the LOD was experimentally determined to be 56 ppm (4.7 muM), equivalent to a RI LOD of 4.5x10(-6) DeltaRI (3sigma). The detection limit for proteins was also found to be favorable. For example, with the current configuration, ribonuclease A (RNAse) had a LOD of 46 ppm (3.4 muM), and bovine serum albumin (BSA) had a LOD of 54 ppm (780 nM). | 18,968,783 |
A sulpha-drug sensitive sensor based on ion-pair complex modified PQC resonator. | The construction and general performance characteristics of the piezoelectric sensors responsive to sulpha-drug are described here. The proposed sensing method is based on the use of the ion-pair complex of sulphadiazine-cetyltrioctylammonium. The complex, together with cholestyramine was embedded in PVC matrix. This sensor exhibited reasonable selectivity and a sensitive mass response to sulpha-drugs. The response range of the sensor was between 1.0x10(-7) and 1.0x10(-5) M with a detection limit of 8x10(-8) M at pH 8.63. The influencing factors were investigated in detail and optimized. | 18,968,793 |
Determination of lysergic acid diethylamide (LSD) by application of online 77 K fluorescence spectroscopy and a sweeping technique in micellar electrokinetic chromatography. | The principal advantage of the use of Shopl'skii effect (low temperature spectrum) is that spectral sharpening occurs both in absorption and emission. However, thus far using the technique of capillary electrophoresis/low temperature fluorescence spectroscopy (CE/LTFS) either at 77 or 4.2 K remains difficult to obtain an on-line spectrum, if the analyte is present at low concentration. This paper examines the feasibility of combining the techniques of online concentration and CE/LTFS to identify LSD and related compounds in urine at 77 K. To improve sensitivity, sweeping-micellar electrokinetic chromatography (sweeping-MEKC) and cation-selective exhaustive injection-sweep-micellar electrokinetic chromatography (CSEI-sweep-MEKC) were used for on-line concentration which resulted in detection limits of approximately 20 approximately 60 ppt, respectively. | 18,968,798 |
Simultaneous determination of uric acid and creatinine in urine by an eco-friendly solvent-free high performance liquid chromatographic method. | A simple, rapid, and eco-friendly analytical method for simultaneous determination of uric acid and creatinine in urine applying high performance liquid chromatography (HPLC) is described. After dilution, de-protein, and filtration, the sample solution was injected to separate the species with C-18 column by an eluent containing 0.05 M ammonium phosphate buffer at pH 7.4. An UV detector was used to monitor the separation of species at 235 nm. Optimum conditions for separation and detection were investigated. Results indicated that under optimized condition measurements were achieved within 13 min. The detection limits were 0.127 and 0.156 mug ml(-1) for uric acid and creatinine respectively. The recovery was 95% (0.57% RSD) for uric acid and 99.2% (0.98% RSD) for creatinine, from five measurements. Real urine specimens were tested. | 18,968,800 |
Voltammetric determination of diethylstilbestrol at carbon paste electrode using cetylpyridine bromide as medium. | In this paper, the voltammetric properties of diethylstilbestrol (DES) at the carbon paste electrode were described. The oxidation peak currents of DES increase significantly in the presence of surfactant cetylpyridine bromide (CPB), compared with that in the absence of CPB. Based on this fact, a voltammetric technique for determining DES is proposed. The accumulation potential has no effects on the peak current of the DES. An open-circuit accumulation is carried out. The experimental parameters, such as pH value of buffer, scan rate, and accumulation time were optimized. The interferences of some metal ions and organic compounds have also been studied, and some metal ions almost do not interfere with the determination of DES. Using this voltammetric method, DES in the injection sample was measured. The results show that this voltammetric method is reliable for the practice determination of DES. | 18,968,804 |
N,N'-disalicylidene-1,3-diaminopropane as a selective chelating titrant for copper(II). | This study was carried out to develop a new complexometric titration method for determination of copper. For this purpose, the standard solutions of copper(II) (10(-3)-10(-5) M) were potentiometrically titrated using N,N'-disalicylidene-1,3-diaminopropane (Schiff base) as titrant and copper(II)-selective electrode for end-point indication in both ammonium acetate and ammonia/ammonium chloride buffer media. The stoichiometry of titration reaction and interference effects of some metal ions on titration of copper were discussed. There was a good agreement between the results obtained by the proposed titration method and ethylenediaminetetraacetic acid (EDTA) titration method. The accuracy and precision of Schiff base method were tested by five replicate determinations both on the standard solution of copper(II) and standard reference materials. The results have indicated that the percentage of copper in alloys can be safely determined by using the Schiff base method without interference from many other metals in alloys. | 18,968,809 |
Potentiometric determination of antimony in metal(II) hexafluoroantimonates(V). | The purpose of this study was to develop an accurate and precise analytical procedure for the determination of the content of antimony in coordination compounds of metal(II) hexafluoroantimonates(V) (M(SbF(6))(2) compounds, where M=Mg, Ca, Sr or Ba) synthesized in our laboratory. The major problem was to find an appropriate reagent for reductive decomposition of SbF(6)(-) to Sb(3+) required for the determination of antimony by redox titration. Effective reduction of Sb(5+) regardless of the metal M bound to SbF(6)(-) species was achieved using metallic aluminium powder in acidic medium. Precipitated Sb(0) was quantitatively reoxidized to Sb(3+) and determined potentiometrically with KBrO(3) or KMnO(4). Other metals were determined complexometrically with disodium ethylenediaminetetraacetic acid (EDTA). Highly accurate and reproducible results were obtained in the concentration range 5-25 mg Sb with an RSD smaller than 0.6%. Antimony-fluoro-hydroxo species and fluoride did not interfere with the complexometric determinations of other metals with EDTA. The developed method enabled, for the first time, complete elemental chemical analysis of M(SbF(6))(2) compounds in the bulk form. | 18,968,810 |
Long pathlength absorbance spectroscopy: trace copper analysis using a 4.4 m liquid core waveguide. | Procedures are described for measurement of dissolved copper with long pathlength Teflon AF-2400 liquid core waveguides. Using a 4.4 m waveguide, absorbance versus concentration is linear for copper concentrations between 1 and 160 nM. The molar absorbance of copper complexed with bathocuproine disulfonate is nearly identical for pathlengths between 1 cm and 4.4 m. Our 4.4 m waveguide system provided a 0.4 nM detection limit with no sample preconcentration. The methods developed in this study have been used to determine copper concentrations in natural seawater, river water, and commercial drinking water. | 18,968,821 |
Effects of different parameters on supercritical fluid extraction of steroid drugs, from spiked matrices and tablets. | Feasibility of supercritical CO(2) extractions of two steroid drugs, medroxyprogesterone acetate (med) and cyproterone acetate (cyp), were evaluated. The effects of temperature (308-348 K), pressure (100-300 bar), static extraction time (5-15 min), dynamic extraction time (10-30 min) and percent methanol modifier (1-10% v/v) on the SFE recoveries of these drugs from spiked matrices (glass) and pharmaceutical dosages (tablets) were investigated. The results showed that minor structural differences between related compounds might lead to dramatically differences in extraction behaviors under the same conditions. The optimum SFE conditions to extract the drugs from spiked glass were 10 min static, 30 min dynamic, 300 bar, 348 K and 5% modifier in the case of med acetate and 10 min static, 30 min dynamic, 100 bar, 308 K, and 10% modifier in the case of cyp. Under these conditions above 90% of the total recovery was obtained for both drugs. Extractions from pharmaceutical dosages were less efficient compared to glass beads under the same conditions. Quantitative recovery of solutes from tablets were obtained upon changing extraction conditions to: 15 min static, 45 min dynamic, P=300 bar, 20% modifier (for med) and 10% (for cyp). | 18,968,834 |
Simple flow injection system for colorimetric determination of iodate in iodized salt. | This work presents a flow injection (FI) system that was developed for determination of iodate. The system utilizes the oxidation of iodide by the analyte to iodine, which subsequently forms tri-iodide. In the presence of starch, the blue I(3)(-)-starch complex is developed within the sample zone and can be colorimetrically detected at 590 nm. Optimization was carried out to make the system suitable for quantitating iodate added to table salts. To prevent accumulation of the blue complex residue on walls of tubing and the flow cell, a port was placed in the system for injection of 10(-3) M thiosulfate plug (100 mul). An injection of this cleaning solution after each sample injection is recommended to avoid positive baseline shift. By means of the paired t-test, the amounts of iodine (mg I kg(-1)) were statistically compared with the results determined by titration and by iodide ion selective electrode. No significant disagreement at 95% confidence was observed. The proposed system is very simple, uses common chemicals and provides rapid analysis (65 injections per h) with high precision (R.S.D.=0.66%, n=10). A detection limit of 2 mg I kg(-1) salt can be achieved. | 18,968,857 |
Stopped-flow injection simultaneous determination of phosphate and silicate using molybdenum blue. | Kinetic information for the phosphate-molybdate-ascorbic acid reaction can be obtained by making use of a very simple manually operated stopped-flow injection (FI) system. Various parameters (concentrations of reagents, flow rate, mixing coils, and volume of flow cell) were investigated for determination of phosphate. A stopped-FI system should be arranged for low degree of mixing (of reactants) and low dispersion so that good signals of rate changes will be observed. Simultaneous determination of phosphate and silicate by the stopped-FI technique is proposed, using a laboratory-made semi-automatic stopped-FI Analyzer with LED-based photometer. It is based on kinetic separation of phosphate and silicate using molybdenum blue. The proposed procedure has been demonstrated for the application to water samples. The results obtained agree with that of a standard method. | 18,968,871 |
Continuous-flow extraction system for elemental association study: a case of synthetic metal-doped iron hydroxide. | A continuous-flow extraction system originally developed for sequential extraction was applied to study elemental association of a synthetic metal-doped amorphous iron hydroxide phase. The homogeneity and metal association of the precipitates were evaluated by gradual leaching using the system. Leachate was collected in fractions for determination of elemental concentrations. The result obtained as extractograms indicated that the doped metals were adsorbed more on the outermost surface rather than homogeneously distributed in the precipitates. The continuous-flow extraction method was also used for effective removal of surface adsorbed metals to obtain a homogeneous metal-doped synthetic iron hydroxide by a sequential extraction using acetic acid and small volume of hydroxylamine hydrochloride solution. The system not only ensures complete washing, but the extent of metal immobilization in the synthetic iron hydroxide could be determined with high accuracy from the extractograms. The initial metal/iron mole ratio (M/Fe) in solution affected the M/Fe mole ratio in homogeneous doped iron hydroxide phase. The M/Fe mole ratio of metal incorporation was approximately 0.01-0.02 and 0.03-0.06, for initial solution M/Fe mole ratio of 0.025 and 0.100, respectively. | 18,968,876 |
SOLVERSTAT: a new utility for multipurpose analysis. An application to the investigation of dioxygenated Co(II) complex formation in dimethylsulfoxide solution. | A new utility for multipurpose analysis, SOLVERSTAT, taking advantage of the versatility of spreadsheets is here described. By means of this tool advanced statistical tests have introduced in Microsoft Excel Solver thus allowing regression diagnostic and discrimination between different models. The utility is here applied to the determination, by UV-Vis spectroscopy, of the stability constant for the uptake of molecular dioxygen by the 1:2 complex of Co(II) with N,N'-dimethylethylenediamine (dmen) in the aprotic solvent dimethylsulfoxide (dmso) at 298 K and in a medium adjusted to 0.1 mol dm(-3) with Et(4)NClO(4). The reliability of the model and parameters obtained are discussed and the results compared with those obtained by Dynafit, a different software package, and by independent voltammetric measurements. The validity of SOLVERSTAT has been also examined applying it to the discrimination between different models already discussed in the literature. | 18,968,885 |
A mercury(II) ion-selective electrode based on neutral salicylaldehyde thiosemicarbazone. | A new ion-selective PVC membrane electrode based on salicylaldehyde thiosemicarbazone as an ionophore is developed successfully as sensor for mercury(II) ions. The electrode shows excellent potentiometric response characteristics and displays a linear log[Hg(2+)] versus EMF response over a wide concentration range of 1.778x10(-6)-1.0x10(-1) M with Nernstian slope of 29 mV per decade with the detection limit of 1.0x10(-6) M. The response time of the electrode is less than 30 s and the membrane electrode operates well in the pH range of 1.0-3.0. The lifetime of the sensor is about 2 months. The electrode shows better selectivity towards Hg(2+) ions in comparison with the alkali, alkaline and some heavy metal ions; most of these metal ions do not show significant interference (K(Pot)(Hg,)(M) values of the order of 10(-3)-10(-4)). The present sensor showed comparable or even better performance vis-à-vis similar PVC based ion-selective electrodes reported in literature. The sensor was also applied as an indicator electrode for potentiometric titration of Hg(2+)ions with I(-) and Cr(2)O(7)(2-). | 18,968,889 |
The quantification of sodium in mineral waters using a quartz crystal microbalance. | A sensor for sodium based on a piezoelectric quartz crystal is proposed. The quartz crystal was coated with 5% of bis[(12-crown-4)methyl] dodecylmethylmalonate, 33% of PVC and 62% of NPOE to which KTpClPB in a 22% molar proportion to the ionophore was added. Coating amounts producing a frequency decrease around 18 kHz show optimum linear calibration ranges for the analysis of sodium in commercial mineral waters. Besides sensitivity, coating stability and selectivity of the sensor over other cations were adequate for those analyses. The results obtained analysing commercial mineral waters by the proposed method are not significantly different (alpha=0.05) from the ones obtained by atomic spectrometry. | 18,968,905 |
Analysis of 2,4,6-trinitrotoluene, pentaerythritol tetranitrate and cyclo-1,3,5-trimethylene-2,4,6-trinitramine using negative corona discharge ion mobility spectrometry. | In this study, the capability of negative corona discharge ion mobility spectrometry (IMS) for quantitative magnitude of several explosives including 2,4,6-trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN) and cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX) has been evaluated for the first time. The total current obtained with the negative corona discharge was about 100 times larger than that of IMS based on (63)Ni, which results in a lower detection limit and a wider linear dynamic range. The detection limits for PETN, TNT and RDX were 8x10(-11), 7x10(-11) and 3x10(-10) g, respectively. The calibration plots for these explosives showed linear dynamic ranges of about four orders of magnitude. | 18,968,915 |
Rapid sample digestion by fusion and chemical separation of Hf for isotopic analysis by MC-ICPMS. | A new method for rapid sample digestion and efficient chemical separation of Hf and REE from rock samples for precise isotopic analysis is presented. Samples are digested by fusion in the presence of a lithium borate flux at 1100 degrees C and dissolved whilst molten in dilute nitric or hydrochloric acid. Prior to chemical separation using ion exchange techniques, Li and B from the flux material and Si from the sample are separated from the remaining major elements, REE and high field strength elements (HFSE) in the sample by Fe-hydroxide co-precipitation. The chemical separation of Hf is a two-stage procedure designed to first remove the remaining matrix elements (e.g. Fe, Ba) in the sample using standard cation exchange techniques, followed by separation of Hf from the REE and HFSE on TEVA extraction chromatographic resin. Hf yields are >90% and total procedural blanks are ca. 50 pg. Hf isotope ratios of a synthetic standard solution and replicate digestions of international rock standards BHVO-1 and BCR-1 measured on multi-collector inductively coupled plasma mass spectrometer (MC-ICPMS) reproduce similarly to </=50 ppm (2 S.D.). The following elemental ratios are routinely obtained for elements, which interfere isobarically or may affect the ionisation and/or fractionation behaviour of Hf during analysis: (176)Yb/(176)Hf<0.0001; (176)Lu/(176)Hf<0.00001; Ti/Hf<0.05. This technique also provides a means of separating Nd from the REE fraction for isotopic analysis and, potentially, may be adapted for measurement of Lu/Hf ratios by isotope dilution techniques. | 18,968,919 |
Application of a classical least-squares regression method to the assay of 1,4-dihydropyridine antihypertensives and their photoproducts. | A multicomponent UV spectrophotometric method using a classical least-squares (CLS) algorithm has been developed for the quantitative determination of 1,4-dihydropyridine (DHP) calcium antagonists and respective photoproducts. The procedure was optimized by defining a fractionation scheme for selecting the more useful wavelength ranges to be used in the calibration model. The method is potentially able to be extended to the other drugs of the same family. The recovery values from synthetic mixtures and commercial formulations were verified to be 99.09 and 97.85% for drug parents and degradation products, respectively. The sensitivity for the photoproducts determination was found to be below 0.8%. The results obtained from laboratory mixtures and commercial formulations were compared with those provided by UV derivative spectrophotometry. | 18,968,920 |
Strategies for developing NADH detectors based on Meldola Blue and screen-printed electrodes: a comparative study. | Three strategies have been compared to produce screen-printed amperometric detectors for NADH: mixing Meldola Blue (MB) in the screen-printing ink, incorporation of MB-Reinecke salt (MBRS) in the graphite ink and electrodeposition of films of MB-derived polymer (poly (MB)) on electrode surface. Following modification of graphite electrodes the mediators displayed values of the formal potential E degrees ' from -0.129 to -0.160 V vs. Ag/AgCl and pK(a)s of 5.09-6.02. A second redox couple with E degrees '=-0.450 V vs. Ag/AgCl was observed in cyclic voltammetry experiments with poly (MB) sensors or with old electrodes obtained according to the other two strategies. Electropolymerisation of MB allowed to achieve the best operational stability and best detection limit, 2 x 10(-6) M, for amperometric detection of NADH, while the most extended linear range, 1 x 10(-5)-7.5 x 10(-4) M, corresponds to sensors with MBRS. MB and MBRS electrodes were compared with a similar NADH detector produced by Gwent Electronic Materials, England. Several characteristics of the modified-electrodes induced by the fabrication by screen-printing were also highlighted. | 18,968,963 |
Factorial designs applied to the development of a capillary electrophoresis method for the analysis of zinc, sodium, calcium and magnesium in water samples. | The aim of this work was to study the influence of several both chemical and instrumental variables for the development of a new capillary electrophoresis (CE) method for the determination of zinc, sodium, calcium and magnesium in water samples by using 1,10-phenanthroline as complexing agent and UV photometric detection at 214 nm. Due to the number of parameters involved and their interactions, factorial experimental designs at two levels have been applied to investigate the influence of several experimental variables (concentration of complexing agent, concentration of a visualisation agent, pH, sample introduction, applied voltage and capillary length) in sets of several capillary electrophoretic responses. The method was applied to the simultaneous determination of Na(I), Ca(II), Mg(II) and Zn(II) in drinking water with satisfactory results and a detection limit of 32 ng ml(-1) for Zn(II) was obtained. | 18,968,965 |
Fast microwave-assisted free sugars washing and hydrolysis pre-treatment for the flow injection determination of starch in food. | The approach used consists of a flow injection (FI) manifold assisted by a focused microwave digestor for both fast washing of free sugars and acceleration of the hydrolysis step prior to the determination of starch in food. The action of microwaves reduces both the times for removal of free sugars to a 5 min single washing cycle with ethanol/water and that of the subsequent starch hydrolysis to a 10 min step. The sugars formed in the starch hydrolysis are in-line derivatised and photometrically monitored at lambda=460 nm. In this way, automation of pre-treatment and determination is achieved with the minimum of both cost and time. The precision of the overall method, expressed as relative standard deviation, is 3.75% and the total analysis time is 38 min. Comparison of the results, obtained in applying the method to flour and bread, is in agreement with those provided by the manual method. | 18,968,971 |
Flow analysis-hydride generation-Fourier transform infrared spectrometric determination of antimony in pharmaceuticals. | In this work, a flow analysis system with hydride generation and Fourier transform infrared (FTIR) spectrometric detection has been developed for the determination of antimony in pharmaceuticals. The method is based on the on-line mineralization/oxidation of the organic antimonials present in the sample and pre-reduction of Sb(V) to Sb(III) with K(2)S(2)O(8) and KI, respectively; prior to the stibine generation. The gaseous SbH(3) is separated from the solution in a gas phase separator, and transported by means of a nitrogen carrier into a short pathway (10 cm) IR gas cell, where the corresponding FTIR spectrum is acquired by accumulating 3 scans in a continuous mode. The 1893 cm(-1) band was used for the quantification of the antimony. The procedure is carried out in a closed system, which reduces sample handling and makes possible the complete automation of the antimony determination. The figures of merit of the proposed method (linear range: 0-600 mg l(-1), limit of detection (3sigma)=0.9 mg l(-1), limit of quantification (10sigma)=3 mg Sb l(-1), precision (R.S.D.) less than 1% and sample frequency=28 h(-1)), are appropriate for the designed application. Furthermore, precise and accurate results were found for the analysis of different antimonial pharmaceutical samples, indicating that the methodology developed represents a valid alternative for the determination of antimony in pharmaceuticals, which could be suitable for the routine control analysis. | 18,968,981 |
Determination of matrine in rat plasma by high-performance liquid chromatography and its application to pharmacokinetic studies. | A simple high-performance liquid chromatography (HPLC) method is described for the determination of matrine in rat plasma. The plasma was deproteinized with acetonitrile that contained an internal standard (phenacetin) and was separated from the aqueous layer by adding sodium chloride. Matrine was extracted into the acetonitrile layer with high yield, and determined by reversed-phase HPLC (column: YMC-pack ODS-A, 5 microm, 150 x 4.6 mm, I.D.; eluent: acetonitrile-0.02 mol ammonium acetate buffer-triethylamine (35:65:0.035, v/v/v) and ultraviolet detection (220 nm). The limit of quantitation for matrine was 200 ng ml(-1) in plasma, and the recovery was greater than 89%. The assay was linear from 0.5 to 50.0 microg ml(-1). Variation over the range of the standard curve was less than 6%. The method was used to determine the concentration-time profiles of matrine in the plasma following oral administration of matrine aqueous solution or bolus injection from which the fractions of matrine reaching the systemic circulation were estimated by a deconvolution method for the first time. | 18,968,986 |
Mercury(II) ion-selective polymeric membrane sensor based on a recently synthesized Schiff base. | A new polyvinyl chloride (PVC) membrane electrode that is highly selective to Hg(II) ions was prepared by using bis[5-((4-nitrophenyl)azo salicylaldehyde)] (BNAS) as a suitable neutral carrier. The sensor exhibits a Nernstian response for mercury ions over a wide concentration range (5.0x10(-2)-7.0x10(-7) M) with a slope of 30+/-1 mV per decade. It has a response time of <10 s and can be used for at least 3 months without any measurable divergence in potential. The electrode can be used in the pH range from 1.0 to 3.5. The proposed sensor shows fairly good discriminating ability towards Hg(2+) ion in comparison with some hard and soft metals. The electrode was used in the direct determination of Hg(2+) in aqueous solution and as an indicator electrode in potentiometric titration of mercury ions. | 18,969,027 |
Acid-base equilibria of phthalic acid in saline media: ion association from Pitzer equations. | The protonation constants of 1,2-benzenedicarboxylic acid (phthalic acid) at 25 degrees C in NaCl and CaCl(2) (ionic strengths ranging from 0.1 to 2 mol kg(-1)) were determined potentiometrically, and the results were analyzed by means of Pitzer equations. The values of the logarithm of the first and second dissociation constants ranged from 2.730 and 4.948 (in 0.101 mol kg(-1) NaCl) to 2.449 and 3.984 (in 0.624 mol kg(-1) CaCl(2)), respectively. Tabulated interaction parameters for the inorganic species involved along with salting coefficients estimated from literature allowed the calculation of new interaction parameters for the phthalate-Na(+)/Ca(2+) systems. The specific ion interaction model considered seems to account for the influence of the formation of weak complexes of phthalate with calcium ions on the equilibrium constants. | 18,969,029 |
Evaluation of different permanent modifiers for the determination of arsenic in environmental samples by electrothermal atomic absorption spectrometry. | Single noble metal permanent modifiers such as, Rh, Ir, and Ru, as well as mixed tungsten plus noble metal (W-Rh, W-Ru, W-Ir) permanent modifiers thermally deposited on the integrated platform of transversally heated graphite atomizer were employed for the determination of arsenic in sludges, soils, sediments, coals, ashes and waters by electrothermal atomic absorption spectrometry. Microwave digests of solid samples and water samples were employed for obtaining the analytical characteristics of the methods with different permanent modifiers. The performance of the modifiers for arsenic determination in the real samples depended strongly on the type of permanent modifier chosen. The single noble metal (Rh, Ir and Ru) permanent modifiers were suitable for the analyte determinations in simpler matrices such as waters (recoveries of certified values 95-105%), but the analyte recoveries of certified values in sludges, soils, sediments, coals, and ashes were always lower than 90%. On the other hand, for the determination of arsenic, using W-Rh, W-Ru, and W-Ir permanent modifiers presented recoveries of certified values within 95-105% for all the samples. Long-term stability curves obtained for the determination of arsenic in environmental samples with different permanent modifiers (Rh, Ir, Ru, W-Rh, W-Ir, W-Ru) showed that the improvement in the tube lifetime depends on the tungsten deposit onto the platform. The tungsten plus noble metal permanent modifier presents a tube lifetime of at least 35% longer when compared with single permanent modifier. The results for the determination of As employing different permanent modifiers in the samples were in agreement with the certified reference materials, since no statistical differences were found after applying the paired t-test at the 95% confidence level. | 18,969,030 |
Analysis of polycyclic aromatic hydrocarbons in HPLC fractions by laser-excited time-resolved Shpol'skii spectrometry with cryogenic fiber-optic probes. | Laser-excited time-resolved Shpol'skii spectrometry at liquid helium temperature (4.2 K) is presented for the analysis of polycyclic aromatic hydrocarbons in high-performance liquid chromatography fractions. Fluorescence measurements are rapidly done with the aid of a fiber-optic probe, pulsed tunable dye laser, spectrograph, and intensified charge-coupled device. Analyte identification and peak-purity checking are made through wavelength-time matrix formats, which give simultaneous access to spectral and lifetime information. Sample preparation is rapid and simple. It involves liquid-liquid extraction or solid-liquid extraction of chromatographic fractions at the tip of the fiber-optic probe. The potential of both approaches is demonstrated with the semi-quantitative analysis of priority pollutants in heavily contaminated water samples. | 18,969,066 |
On-line screening methods for antioxidants scavenging superoxide anion radical and hydrogen peroxide by liquid chromatography with indirect chemiluminescence detection. | The identification of radical species is possible by the electron spin resonance technique. However, the antioxidants in complex matrices such as biological and food samples are difficult to determine. Hence, we developed novel screening systems for antioxidants, which are mainly eliminating superoxide anion radical (O(2)(-)) and hydrogen peroxide (H(2)O(2)), by HPLC with luminol-based chemiluminescence (CL) detection. When the sample contains antioxidants, inhibited peaks corresponding to each antioxidant are observed on the chromatogram. The antioxidant activities of catechins and flavones were determined with flow injection analysis by the proposed indirect CL. The scavenging activity for H(2)O(2) and O(2)(-) were different from each catechin and flavone. Furthermore, the potential was dependent upon the number and the position of OH functional group in the structure. Some applications such as the screening of antioxidants in tea products were also investigated. In spite of many peaks appeared on the chromatogram at UV detection, only the peaks corresponding to the compounds having elimination effect to O(2)(-) and/or H(2)O(2) were detected as inhibited peaks. Consequently, the proposed HPLC-CL seems to provide new screening systems for antioxidants possessing inhibition activity of O(2)(-) and H(2)O(2). | 18,969,068 |
Fluorescence analysis of the interaction of two peptide sequences of hepatitis GB virus C with liposomes. | The physicochemical characterization of the peptide sequences E2 (39-53) and E2 (32-59) corresponding to the structural protein E2 of the GB virus C was done by studying their interaction with model membranes. The peptides showed surface activity concentration dependent when injected beneath a buffered solution. This tendency to accumulate into the air/water interface suggested a potential ability of these peptides to interact with bilayers. For that reason, Small Unilamellar Liposomes (SUVs) of 1,2-dimyiristoyl-sn-Glycero-3-Phosphocholine (DMPC) or 1,2-dimyiristoyl-sn-Glycero-3-[Phospho-rac-(1-glycerol)] (DMPG) were chosen as a mimetic membranes. A series of fluorescence experiments based on tryptophan peptide fluorescence or with fluorescence labeled SUVs, were done to cover different aspects of peptide interaction with bilayers. Steady state fluorescence anisotropy studies with N-(7-nitro-2-1,3-benzoxadiazol-4-yl) dioleoylphosphatidylethanolamine (NBD-PE) or 1-[4-(trimethylammonium) phenyl]-6-phenyl-1,3,5-hexatriene (TMA-DPH) labeled SUVs indicated that only the long peptide was able to change the lipid microenvironment of DMPG vesicles by slightly increasing the rigidity of the bilayer both above and under the lipid main transition temperature. These results were concordant with the slight blue shift of the maximum tryptophan wavelength emission after E2 (32-53) peptide incubation with DMPG vesicles. Our data provide useful information for the design of synthetic immunopeptides that can be incorporated into a liposomal system with a potential to promote a direct delivery of the membrane-incorporated immunogen to the immunocompetent cells, thus increasing the immuno response from the host. | 18,969,070 |
Fluorometric assay of lipoperoxides and chromatographic analysis of alpha-tocopherol and fatty acids as biomarkers of risk from coronary atherosclerosis. | There has been growing interest in the quantitative determination of biochemical predictors of atherogenesis. The aim of the present study was to investigate association of lipoperoxidation biomarkers known to be pro-atherogenic (thiobarbituric acid reactive substance activity, TBARS) or anti-atherogenic (alpha-tocopherol) with the fatty acid status, and relate it to the coronary artery disease (CAD) as assessed by coronary angiography in patients with stable angina pectoris. We found that serum lipoproteins and TBARS did not differ significantly. However there was significant correlation of TBARS with total vitamin E (P=0.02) and vitamin E in very low-density lipoprotein (VLDL) (P=0.02) and low-density lipoprotein (LDL) (P=0.01), with LDL-linoleic acid (P=0.01), and high-density lipoprotein-linoleic acid (P=0.02). There was significant correlation of total vitamin E (P=0.01) and VLDL-vitamin E (P=0.01) with the degree of CAD. We conclude that TBARS and alpha-tocopherol could not be evaluated as biomarkers for the severity of CAD among the patients with stable angina pectoris. | 18,969,072 |
A demonstration model for a selective and recyclable uptake of metals from water: Fe(III) ions complexation and release by a supported natural fluorescent chelator. | We describe here the preliminary stage of development of a process aiming at the selective uptake and release of metal ions from water. The process envisioned involves the encapsulation of highly selective natural chelates secreted by bacteria or other living species in mesoporous solids that could be used as usual resins. To demonstrate the feasibility of the concept, we use a model system involving pyoverdin, a natural Fe(III) ions chelator from a Pseudomonas fluorescens strain, encapsulated in a mesoporous templated silica. For this model study, the native fluorescence of the chelator allows a simpler follow-up and quantification of the uptake and release processes. | 18,969,073 |
Contributions to the determination of histamine rate by measuring out the histamine-orthophthalaldehyde complex in the absorption and fluorescence. | Histamine is an important compound from a physiological point of view, but it is toxic since the absorption of low amounts of histamine can cause abdominal pains accompanied with vomiting. Why we have developed a new method for histamine analysis in order to improve Lerke and Bell method. From the absorption spectra, we showed that the stoichiometry of the complex histamine-orthophthalaldehyde (OPA) is 1:1. From the emission spectra, it was observed that the complex fluorescence is inhibited in acidic medium. In alkaline medium, an exaltation of fluorescence was observed, but the complex histamine-OPA was unstable. Nevertheless, kinetic study showed that good linear correlations between the fluorescence maxima of the formed complex and the histamine concentration could be obtained in this alkaline medium. | 18,969,080 |
Flow injection potentiometry by a new coated graphite ion-selective electrode for the determination of Pb(2+). | A new graphite coated electrode for the determination of Pb(2+) based on a recently synthesized ionophore 1-hydroxy-2-{2-[2-(2-hydroxy-ethoxy)-ethoxy]-ethoxy methyl}-anthracene-9,10-dione (L) has been developed. The electrode was used in flow injection potentiometry by a home-made flow cell. Under both the batch and flow conditions, the electrode revealed a near Nernstian response over a wide lead ion concentration range (10(-6) to 10(-1) M) and very low limit of detection. In flow injection potentiometry, excellent reproducibility (RSD%=0.49%), very high sampling rate (170 injections h(-1)) and stable baseline was observed in the presence of 10(-3) M KCl as ionic strength adjuster. The electrode showed high sensitivity and good selectivity for Pb(2+) over a wide variety of alkali, alkali earth and transition metal ions and the electrode can be used for at least 3 months without any considerable change in potential response. The proposed sensor was successfully applied to the direct determination of lead in real samples and also used for the titrimetric determination of phosphate ions by both batch and flow injection potentiometry. | 18,969,102 |
Molecular orientation of a model liquid crystal alignment layer. | An analytical methodology, involving the use of a combination of second harmonic generation (SHG) and linear dichroism, was utilized to probe the molecular orientation and angular distribution of a model liquid crystal (LC) alignment layer. In order to determine which film structure would be best suited for use as an alignment layer, the azo dye o-methyl red (MR) was covalently bound to a glass substrate using both monofunctional and trifunctional silane chemistry. The influence of solvent on the orientation and angular distribution of both thin films was also investigated. For the monofunctional silane film under water, the mean orientation angle of the MR molecular long axis was 67+/-4 degrees and the width of an assumed Gaussian distribution was 32+/-2 degrees . Under hexanes, the mean orientation angle was the same within error (63+/-1 degrees ) but the distribution width narrowed considerably to 22+/-1 degrees . Molecular orientation within the trifunctional silane film exhibited little dependence on solvent. Under water, the mean orientation angle and angular distribution width were 76+/-3 degrees and 30+/-1 degrees , respectively. With hexanes as the solvent, the mean orientation angle and angular distribution width were 79+/-1 degrees and 30+/-1 degrees , respectively. Orientation insensitive SHG measurements indicated that surface coverage in the tri-functional silane film was twice that in the mono-functional silane film. The observed orientational differences were attributed to differences in the forces that dictate molecular orientation for the two systems. Based on the higher orientation angle, higher surface coverage and the lack of solvent dependence, MR-tri exhibits more desirable characteristics for use as an LC alignment layer. | 18,969,104 |
Simultaneous determination of orthophosphate and total phosphates (inorganic phosphates plus purine nucleotides) using a bioamperometric flow-injection system made up by a 16-way switching valve. | Orthophosphate and total phosphates (inorganic phosphates plus purine nucleotides) can be determined simultaneously in a novel flow-injection system made up by a 16-way switching valve with two sample loops, acid phosphatase (AcP) immobilized reactor and a delay coil needed to separate two peaks corresponding to two sample portions injected simultaneously. An orthophosphate enzyme electrode with a hybrid membrane of trienzyme film and poly(1,2-diaminobenzene) film was used to selectively detect both the endogenous orthophosphate and orthophosphate generated enzymatically into the AcP immobilized reactor, without any interferences from electroactive species, such as ascorbate and urate. Because two sample portions passed through the flow line with different residence time, two peaks were obtained. The first peak corresponded selectively to orthophosphate and the second peak to the total of inorganic phosphates and purine nucleotides. The maximum currents of both peaks were linearly related to the concentration of orthophosphate and total phosphates (as orthophosphate) in the range 5x10(-7)-8x10(-4) M, respectively; 30 samples per hour can be processed with an R.S.D. <2.5%. | 18,969,109 |
Application of flowing stream techniques to water analysis. Part I. Ionic species: dissolved inorganic carbon, nutrients and related compounds. | This paper summarizes the most relevant manuscripts issued from 1990 to date referred to water analysis using flowing stream techniques. Concretely, reported flow methods applied to the determination or monitoring of inorganic analytes (viz. carbon, nitrogen, phosphorous and silicon species) together with some related compounds to assess water quality in drinking, rain, underground, marine, river, estuarine, waste and industrial samples are reviewed. For the first time, the most widespread flow techniques of analysis described in the literature (viz. segmented flow analysis (SFA), continuous flow analysis (CFA), flow injection analysis (FIA), sequential injection analysis (SIA), multicommuted FIA (MCFIA), multisyringe FIA (MSFIA), along with the different exploited injection modalities are included in the same review. | 18,969,112 |
Selective pre-concentration of selenite from aqueous samples using mercapto-silica. | Silica gel modified with 3-mercaptopropyl-trimethoxysilane was used for the selective separation and pre-concentration of selenite (Se(IV)) from aqueous solutions containing Se(IV) and selenate (Se(VI)). Over a wide range of acidity, from 2 mol l(-1) HCl to pH 9.00, Se(IV) was taken up by the mercaptopropyl-silica with nearly 100% efficiency; Se(VI) however was unretained. Se(IV) content was determined by hydride generation atomic absorption spectrometry (HGAAS), following batch release of the selenium from the pre-concentration medium by acidic periodate. The overall pre-concentration efficiency, including both take-up and elution, in the range of 89-106%. The method was applied to spiked seawater samples containing as low as 800 ng l(-1) Se in selenite form. This solid-phase extraction system offers several major advantages over conventional solvent extraction procedures. It firstly exhibits high selectivity for Se(IV) over Se(VI). Using the solid-phase media, pre-concentration of Se(IV) in dilute water samples can be carried out in the field, stabilizing the selenite-selenium in a convenient form for transport and storage. In addition, selenium stored on silica is derived solely from Se(IV) overcoming problems of selenium redox speciation changes and loss during storage. | 18,969,126 |
Membrane electrodes sensitive to doubly charged surfactants. Application to a cationic gemini surfactant. | The response of a membrane electrode is not always identical to that of a redox electrode. Indeed, in the case of membrane electrode the response is not due to a redox equilibrium but to a cross-membrane potential. So, the membrane electrode's response depends mainly on the carrier system and the nature of the membrane. The properties of the membrane can favour several reactions giving rise to different ionic species diffusing in the membrane. The expression of the cross-membrane potential thus depends on the number and quantities of these ionic species. To illustrate this, we established the equations for the case of a two-charge cation detected by a univalent charged carrier. We show that the Nernstian response is not applicable to membrane electrodes. This approach allowed us to interpret results obtained with a cationic gemini surfactant-selective electrode prepared in the laboratory. To prove the well working of this electrode, we determined the critical micelle concentration in water and several NaBr solutions (0.004, 0.006, 0.01 and 0.02 M) from which the counterion binding has been determined. | 18,969,132 |
Two different strategies for the fluorimetric determination of piroxicam in serum. | Two different spectrofluorimetric methods for the determination of piroxicam (PX) in serum are presented and discussed. One of them is based on the use of three-way fluorescence data and multivariate calibration performed with parallel factor analysis (PARAFAC) and self-weighted alternating trilinear decomposition (SWATLD). This methodology exploits the so-called second-order advantage of the three-way data, allowing to obtain the concentration of the studied analyte in the presence of any number of uncalibrated (serum) components. The method was developed following two different procedures: internal standard addition and external calibration with standard solutions, which were compared and discussed. The second approach investigated is based on the combination of solid-phase extraction (SPE) and room temperature fluorimetry. Both methods here presented yield satisfactory results. The concentration range in which PX could be determined in serum was 1-10 microg ml(-1). The limits of quantification for the experimental solutions using the chemometric approach were 0.09 microg ml(-1) for the standard addition mode and 0.12 microg ml(-1) using external calibration (both for PARAFAC and SWATLD algorithms). In the solid-surface fluorimetric method, the calibration graph was linear up to 0.22 microg ml(-1) and the limit of quantification was 0.02 microg ml(-1). | 18,969,137 |
Preparation of multiwall carbon nanotubes film modified electrode and its application to simultaneous determination of oxidizable amino acids in ion chromatography. | A multiwall carbon nanotubes (MWNTs) film modified electrode was prepared and used as an amperometric sensor for the simultaneous determination of oxidizable amino acids including cysteine, tryptophane and tyrosine. The electrochemical behaviors of these amino acids at this modified electrode were studied by cyclic voltammetry (CV). The results indicated that the MWNTs chemically modified electrode (CME) exhibited efficient electrocatalytic activity towards the oxidation of these amino acids with relatively high sensitivity, stability and long-life. Following separation by ion chromatography (IC) with 2.0 x 10(-3) mol l(-1) citric acid buffer solution (pH 6.5) as eluent, cysteine, tryptophane and tyrosine could be determined by the MWNTs CME successfully. Under the optimal conditions, the detection limits were 7.0 x 10(-7) mol l(-1) for cysteine, 2.0 x 10(-7) mol l(-1) for tryptophane and 3.5 x 10(-7) mol l(-1) for tyrosine at the signal-to-noise of 3, respectively. The method was applied successfully to the determination of these substances in plasma. | 18,969,138 |
Determination of phosphate in hydroponic nutrient solutions using flow injection potentiometry and a cobalt-wire phosphate ion-selective electrode. | The direct flow injection potentiometric (FIP) analysis of phosphate in hydroponic nutrient solution has been carried out using a cobalt-wire ion-selective electrode (ISE). Synthetic hydroponic nutrient solution, commercial hydroponic nutrient solution and working hydroponic farm nutrient solution were analysed for phosphate using the FIP technique. It is shown that FIP results compare favourably to standard methods of analysis such as spectrophotometry and indirect photometric ion-pair chromatography. Reproducible FIP response curves with a slope of -(47.57+/-0.03) mV per decade and intercept of -(169.7+/-0.1) mV were obtained for four separate calibrations in the concentration range 5.0 x 10(-4)-1.0 x 10(-2) M H(2)PO(4)(-). Anion corrections for interferences by Cl(-), NO(3)(-) and SO(4)(2-) were applied to all samples using the selectivity coefficients determined independently using a fixed interference method. Nevertheless, it was found that anion corrections were not necessary, as the deviations fell within the bounds of experimental error for the cobalt-wire ISE technique (i.e.+/-2-5% R.S.D.). The proposed FIP method enables the direct determination of phosphate in hydroponic nutrient solutions. | 18,969,148 |
Novel flow injection-fluorometric method for the determination of trace silicate and its application to ultrapurified water analysis. | A highly sensitive fluorescence quenching method for the determination of silicate based on the formation of an ion associate between molybdosilicate and Rhodamine B (RB) in nitric acid medium was developed. A flow injection system coupled with a fluorescence detector was used for the measurement of fluorescence intensity at 560 and 580 nm as excitation and emission wavelengths, respectively. The calibration graph for Si showed a linear range of 0.1-5 ng cm(-3) with correlation coefficient of 0.9999, and the detection limit of 0.06 ng cm(-3). The proposed method was successfully applied to the determination of silicate in ultrapurified water with satisfactory results. | 18,969,155 |
Development of a catalase based biosensor for alcohol determination in beer samples. | An amperometric biosensor based on catalase enzyme for alcohol determination was developed. To construct the biosensor catalase was immobilized by using gelatin and glutaraldehyde on a Clark type dissolved oxygen (DO) probe covered with a teflon membrane which is sensitive for oxygen. The working principle of the biosensor depends on two reactions, which one is related to another, catalyzed by catalase enzyme. In the first reaction catalase catalyzes the degradation of hydrogen peroxide and oxygen is produced and also a steady-state DO concentration occurs in a few minutes. When ethanol added to the medium catalase catalyzes the degradation of both hydrogen peroxide and ethanol and this results in a new steady-state DO concentration. Difference for first and the last steady-state DO concentration occurred in the interval surface of DO probe membrane, which related to ethanol concentration, are detected by the biosensor. The biosensor response depends linearly on ethanol concentration between 0.05 and 1.0 mM with a detection limit of 0.05 mM and a response time of 3 min. In the optimization studies of the biosensor phosphate buffer (pH 7.0; 50 mM) and 35 degrees C were established as providing the optimum working conditions. In the characterization studies of the biosensor some parameters such as reproducibility, substrate specificity, operational and storage stability were carried out. Finally, by using the biosensor developed and enzimatic-spectrophotometric method alcohol concentration of some alcoholic drinks were determined and results were compared. | 18,969,169 |
GFAAS determination of selenium after separation with thiol cotton in lichens and plants: the importance of adding a mineral matrix before decomposition. | This study reports a preparation technique for the determination of Se concentration in lichens and plants, using matrix separation and preconcentration of samples with thiol cotton. Sample digestions were done using HNO(3)-H(2)O(2)-HF. A graphite furnace atomic absorption method has been used for the determination of Se in the different samples. The method was validated through the analysis of four certified reference materials (lichen, grass and sea lettuce) and of four in-house lichen materials. A limit of determination of 0.02 mug g(-1) in the solid sample and a precision (relative standard deviation) varying from 3 to 15% was found through the course of this study. The most important finding resides in the fact that a mineral matrix must be added to the lichen and plant samples before decomposition to obtain high and constant recoveries. | 18,969,170 |
Electrochemistry and electrocatalysis of binuclear cobalt phthalocyaninehexasulfonate-surfactant film modified electrode. | Electrochemistry and electrocatalysis of binuclear cobalt phthalocyaninehexasulfonate sodium salt (bi-CoPc) were investigated successfully in liquid crystal films of didodecyldimethylammonium bromide (DDAB) on pyrolytic graphite (PG) electrodes in aqueous solution. This new bi-CoPc-surfactant film modified electrode could reduce aggregation of bi-CoPc in aqueous solution, which was confirmed by the electronic absorption spectra in the visible region and images of transmission electron microscopy (TEM). The charge transport diffusion coefficient (D(ct)) and apparent heterogeneous electrode reaction rate constant (k(s)) for this modified electrode were estimated. The reduction of bi-CoPc ligand showed excellent electrocatalytic ability for the reduction of trichloroacetic acid (TCA) and catalytic current had a linear relationship with the concentration of TCA in the range of 3x10(-5)-7.5x10(-3) M. The reduction of bi-Co(III)Pc/bi-Co(II)Pc couple exhibited new pattern of catalytic reactivity in the reduction of oxygen. Peak current for the cathodic reduction of oxygen is proportion to the square root of the scan rate in the range of 5-1000 mV s(-1) in oxygen-saturated solution. | 18,969,184 |
Optimum phase-behavior formulation of surfactant/oil/water systems for the determination of chromium in heavy crude oil and in bitumen-in-water emulsion. | An "oil in water" formulation was optimized to determine chromium in heavy crude oil (HCO) and bitumen-in-water emulsion (Orimulsion-400(R)) samples by transversally heated electrothermal atomic absorption spectrometry (TH-ET AAS) using Zeeman effect background correction. The optimum proportion of the oil-water mixture ratio was 7:3 v/v (70 ml of oil as the internal phase) with a non-ionic surfactant concentration (Intan-100) in the emulsion of 0.2% w/w. Chromium was determined in different crude oil samples after dilution of the emulsions 1:9 v/v with a 0.2% w/w solution of surfactant in order to further reduce the viscosity from 100 to 1.6 cP and at the same time to bring the concentration of chromium within the working range of the ET AAS technique. The calibration graph was linear from 1.7 to 100 mug Cr l(-1). The sensitivity was of 0.0069 s l mug(-1), the characteristic mass (m(o)) was of 5.7 pg per 0.0044 s and the detection limit (3sigma) was of 0.52 mug l(-1). The relative standard deviation of the method, evaluated by replicate analyses of three crude oil samples varied in all cases between 1.5 and 2.6%. Recovery studies were performed on four Venezuelan crude oils, and the average chromium recovery values varied between 95.9-104.8, 90.6-107.6, 95.6-104.0 and 98.8-103.9% for the Cerro Negro, Crudo Hamaca and Boscán crude oils and for the Orimulsión(R)-400, respectively. The results obtained in this work for the Cerro Negro, Crudo Hamaca and Boscán crude oils and for the Orimulsión(R)-400 following the proposed procedure were of 0.448+/-0.008, 0.338+/-0.004 0.524+/-0.021 and 0.174+/-0.008 mg Cr l(-1), respectively, which were in good agreement with the values obtained by a tedious recommended standard procedure (respectively: 0.470+/-0.05, 0.335+/-0.080, 0.570+/-0.021 and 0.173+/-0.009 mg Cr l(-1)). | 18,969,194 |
Biosensors for phenol derivatives using biochemical signal amplification. | Two different approaches, both exploiting two enzymes cooperative functioning, to enhance the sensitivity of tyrosinase (PPO) based biosensor for amperometric detection of phenols have been compared. For this purpose, one monoenzyme electrode (PPO) and two bienzyme electrodes (PPO and d-glucose dehydrogenase, GDH; PPO and horseradish peroxidase, HRP) were constructed using agar-agar gel as enzyme immobilization matrix. The biosensors responses for l-tyrosine detection were recorded at -50 mV versus saturated calomel electrode (SCE). The highest sensitivity (74 mA M(-1)) was observed for the PPO-GDH couple, while that recorded for PPO-HRP couple system was only 32 times higher than that measured for monoenzyme electrode (0.01 mA M(-1)). The ability of the PPO-, PPO-GDH-, PPO-HRP-based biosensors to assay phenols was demonstrated by quantitative determination of phenol, 1,2-dihydroxybenzene, 1,3-dihydroxybenzene, 1,4-dihydroxybenzene, 2-amino-3 (4-hydroxyphenyl) propanoic acid, 2-hydroxytoluene, 3-hydroxytoluene, 4-hydroxytoluene, 4-clorophenol, 3-clorophenol, 2-clorophenol, 4-hydroxybenzoic acid. | 18,969,212 |
A study of bismuth-film electrodes for the detection of trace metals by anodic stripping voltammetry and their application to the determination of Pb and Zn in tapwater and human hair. | This work reports the simultaneous determination of Cd(II), Pb(II) and Zn(II) at the low mug l(-1) concentration levels by square wave anodic stripping voltammetry (SWASV) on a bismuth-film electrode (BFE) plated in situ. The metal ions and bismuth were simultaneously deposited by reduction at -1.4 V on a rotating glassy carbon disk electrode. Then, the preconcentrated metals were oxidised by scanning the potential of the electrode from -1.4 to 0 V using a square-wave waveform. The stripping current arising from the oxidation of each metal was related to the concentration of each metal in the sample. The parameters for the simultaneous determination of the three metals were investigated with the view to apply this type of voltammetric sensor to real samples containing low concentrations of metals. Using the selected conditions, the limits of detection were 0.2 mug l(-1) for Cd and for Pb and 0.7 mug l(-1) for Zn at a preconcentration time of 10 min. Finally, BFE's were successfully applied to the determination of Pb and Zn in tapwater and human hair and the results were in satisfactory statistical agreement with atomic absorption spectroscopy (AAS). | 18,969,224 |
The formation of sparingly soluble species of Ca(2+) with carboxylic ligands: speciation and thermoanalysis. | This work reports the results of studies into the solubility and thermal decomposition of various sparingly soluble complexes of calcium with two isomeric benzene tricarboxylates, and with benzene penta- and hexa-carboxylates. The dependence of their solubility on ionic strength and, for the calcium benzene hexacarboxylate, the dependence of solubility on Na(+) concentration in solution were studied. Comparison between structure and solubility of the calcium insoluble compounds here and previously studied, is also reported. In order to perform solubility calculations, we determined also the formation constants of trimellitic and trimesic anions with H(+), Na(+) and Ca(2+) potentiometrically (H(+)-ISE), since these are not reported in literature. All solid compounds were characterised by TG-FTIR measurements, and comparable behaviours in thermal decomposition as a function of ligand structure were found. | 18,969,225 |
Simultaneous determination of lead, nickel, tin and copper in aluminium-base alloys using slurry sampling by electrical discharge and multielement ETAAS. | The simultaneous multielement determination of Pb, Sn, Ni and Cu in aluminium alloys by electrothermal atomic absorption spectrometry (ETAAS) was performed by a quick method using slurry sampling. The metallic colloidal slurries were obtained by an electrical discharge operated in liquid medium. In this work, the effects of aluminium were evaluated and the results show that it causes a strong retention of Pb, Ni and Cu at low pyrolysis temperatures which is overcome by employing high pyrolysis temperatures. Aluminium also significantly improves the thermal stabilisation of Pb and Sn, it being possible to reach pyrolysis temperatures of 1100 and 1300 degrees C, respectively. Such stabilisation indicates that the performance of aluminium as a matrix modifier for Pb is better than that obtained using phosphate and magnesium nitrate without substantial changes of the figures of merit. The effects of aluminium on the atomisation characteristics of the elements and those coming from the simultaneous multielement determination on the figures of merit of the elements are also discussed. In this work, a calibration procedure involving a matrix matching method with aqueous aluminium standards is proposed as a simple and efficient way to solve the inconveniences originated by the aluminium matrix. The proposed method was applied to the simultaneous multielement determination of several aluminium-base alloy standards giving results well within the recommended values. | 18,969,226 |
Cathodic stripping voltammetry of trace Mn(II) at carbon film electrodes. | A sensitive voltammetric method is presented for the determination of tract levels of Mn (II) using carbon film electrodes fabricated from carbon resistors of 2 Omega. Determination of manganese was made by square wave cathodic stripping voltammetry (CSV), with deposition of manganese as manganese dioxide. Chronoamperometric experiments were made to study MnO(2) nucleation and growth. As a result, it was found to be necessary to perform electrode conditioning at a more positive potential to initiate MnO(2) nucleation. Under optimised conditions the detection limit obtained was 4 nM and the relative standard deviation for eight measurements of 0.22 nM was 5.3%. Interferences from various metal ions on the response CSV of Mn(II) were investigated, namely Cd(II), Ni(II), Cu(II), Cr(VI), Pb(II), Zn(II) and Fe(II). Application to environmental samples was demonstrated. | 18,969,228 |
Concentration of heavy metal ions in water using thermoresponsive chelating polymer. | Thermoresponsive polymers, poly(N-isopropylacrylamide) (PNIPAAm), having chelating functionalities were synthesized. PNIPAAm-imidazole (-Im) was precipitated and formed a gum-like aggregate in the neutral pH region at 50 degrees C, while PNIPAAm-carboxylic acid (COOH) and PNIPAAm-iminodiacetic acid (-IDA) remained soluble even at pH 7. An addition of a paired ion, dodecyltrimethylammonium ion, was effective for inducing the precipitation of those polymers. PNIPAAm-Im was useful for collecting copper(II), nickel(II), cobalt(II), and lead(II), but was ineffective for cadmium(II) recovery. In contrast, PNIPAAm-COOH collected cadmium(II), while insufficiently recovered cobalt(II) and nickel(II). PNIPAAm-IDA was the best choice for collecting all metal ions in neutral pH's. After 20-folds concentration, the metal ions in river and seawater were successfully determined by graphite furnace atomic absorption spectrometry (GFAAS). | 18,969,246 |
Copper(I)-bathocuproine complex as carrier in iodide-selective electrode. | A PVC membrane electrode for iodide ions based on Cu(I)-bathocuproine as ionophore in membrane composition is prepared. The electrode exhibits a linear response over a wide concentration range 5.0x10(-6) to 2.0x10(-1)moll(-1) with a detection limit 1.0x10(-6)moll(-1). The proposed membrane electrode shows Nernstian behavior with a slope of -56.8mV/decade, a fast response time 10s and a lifetime at least 3 months. Iodide-selective electrode reveals good selectivities for iodide ion over a wide variety of the other anions and can be used in pH range of 3-9. It can also be used as an indicator electrode in potentiometric titration of iodide ion. | 18,969,284 |
Sulfonylcalix[4]arenetetrasulfonate as pre-column chelating reagent for selective determination of aluminum(III), iron(III), and titanium(IV) by ion-pair reversed-phase high-performance liquid chromatography with spectrophotometric detection. | Sulfonylcalix[4]arenetetrasulfonate (SO(2)CAS) has been examined as a pre-column chelating reagent for ultratrace determination of metal ions by ion-pair reversed-phase high-performance liquid chromatography with spectrophotometric detection. Metal ions were converted into the SO(2)CAS chelates in an acetic buffer solution (pH 4.7). The chelates were injected onto a n-octadecylsilanized silica-type Chromolithtrade mark Performance RP-18e column and were eluted using a methanol (50wt.%)-water eluent (pH 5.6) containing tetra-n-butylammonium bromide (7.0mmolkg(-1)), acetate buffer (5.0mmolkg(-1)), and disodium ethylendiamine-N,N,N',N'-tetraacetate (0.10mmolkg(-1)). Under the conditions used, Al(III), Fe(III), and Ti(IV) were selectively detected among 21 kinds of metal ions [Al(III), Ba(II), Be(II), Ca(II), Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Ga(III), Hf(IV), In(III), Mg(II), Mn(II), Mo(VI), Ni(II), Pb(II), Ti(IV), V(V), Zn(II), and Zr(IV)]. The detection limits on a 3sigma blank basis were 8.8nmoldm(-3) (0.24ngcm(-3)) for Al(III), 7.6nmoldm(-3) (0.42ngcm(-3)) for Fe(III), and 17nmoldm(-3) (0.80ngcm(-3)) for Ti(IV). The practical applicability of the proposed method was checked using river and tap water samples. | 18,969,300 |
Selective labeling of histidine by a designed fluorescein-based probe. | The synthesis of a novel fluorescent probe, 3-epoxypropoxy fluorescein (EPF), and its properties for labeling of histidine are described. The probe contained a fluorescein fluorophore with long-wavelength response and an active epoxy labeling group. In alkaline media EPF reacted selectively with histidine, rather than with other amino acids, causing a large increase in fluorescence intensity and thereby allowing a selective detection of histidine. This fluorescence increase resembled that of the fluorescein diaion with the increase of the media basicity, suggesting that the addition reaction of histidine with the epoxy group provides the fluorophore moiety with a basic molecular environment. As an application of this probe, fluorescent labeling of histidine in human serum was attempted and the obtained results were in agreement with those given by using histidine-nickel complex adsorptive voltammetry. Further, the relative S.D. of the method was 1.8% for 10 replicate determinations of 0.55 muM histidine. When 10muM of EPF was used, the linear range for histidine was 0.007-10muM with a detection limit (S/N=3) of 0.001muM. | 18,969,304 |
Assessment of heavy metals leachability from metallo-organic sorbent-iron humate-with the aid of sequential extraction test. | The sequential extraction test, known as a BCR procedure, was used to assess a leachability of heavy metals (Zn, Cd, Pb, Cu) from the metallo-organic sorbent-iron humate-loaded with these metals. The sequential test allowed to discriminate between various fractions of heavy metals, namely the acid-extractable fraction, the fraction bound to Fe oxides, and the fraction bound to organic matter. It was proven that the heavy metals are bound mainly to Fe oxides and organic matter, and thus they may be relatively hardly liberated into the environment. The BCR sequential extraction test exhibited a very good repeatability, when it was applied to the loaded sorbent-relative standard deviations were typically lower than 10%. | 18,969,324 |
Optimization of smoothing process-the method to improve calibration in voltammetry Part I. Simulated voltammograms. | The problem of the optimal choice of algorithmic filter and the evaluation of smoothing effects in voltammetry is studied. The basic idea of the optimization is an investigation of the improvement of the calibration and the recovery functions parameters during denoising process. The evaluation routine yields the answer in numerical form and may be used for the best filter selection. In order to show how the proposed criterion operates, it was applied to the simulated curves which were peak shaped and distorted by noise of different type and amplitude. Results were compared to the other method based on difference between true and denoised signal. The described tool may be applied for the automatic signal processing. | 18,969,334 |
Synthesis and characterization of electrochemiluminescent ruthenium(II) complexes containing o-phenanthroline and various alpha-diimine ligands. | A series of o-phenanthroline-substituted ruthenium(II) complexes containing 2,2'-dipyridyl, 2-(2-pyridyl)benzimidazole, 2-(2-pyridyl)-N-methylbenzimidazole, 4-carboxymethyl-4'-methyl-2,2'-dipyridyl, and/or 4,4'-dimethyl-2,2'-dipyridyl ligands were synthesized and examined as potent electrochemiluminescent (ECL) materials. The characteristics of these complexes, regarding their electrochemical redox potentials and relative ECL intensities for tripropylamine were studied. As found in a 2,2'-bipyridyl-substituted ruthenium(II) complexes, a good correlation between the observed ECL intensity and the donor ability of alpha-diimine ligands was observed, i.e., the ECL intensity of the Ru(II) complex decreased with an increase in the ligand donor ability. The ECL efficiency increased as the number of substitutions of o-phenanthroline (o-phen) to metal complexes increased. | 18,969,335 |
Simultaneous determination of tin, germanium and molybdenum by diode array detection-flow injection analysis with partial least squares calibration model. | Simultaneous determination of tin, germanium and molybdenum in food samples has been established by flow injection-charge coupled detector (CCD) diode array detection spectrophotometry with partial least squares (PLS) algorithm. The method was based on the chromogenic reaction of metal ions and salicylflurone in the presence of cetyltrimethyl ammonium bromide. The overlapping spectra of these complexes are collected by CCD diode array detector and the multi-wavelength absorbance data are processed using partial least squares algorithm. The reaction conditions and analytical parameters of flow injection analysis have been investigated. The method was applied to directly determine Ge, Mo and Sn in several food samples after digestion with satisfactory results. The recoveries of spiked samples were 80.0-102.0% for tin, 86.3-92.0% for germanium and 83.2-95.2% for molybdenum, and the relative standard deviations for samples were 4.4-7.8%. Molybdenum in certified reference material of cattle liver was determined by the proposed method (n=8). The differential values between determined and guarantee values were within the given uncertain value ranges (t=1.687, P>0.05 for t-test). The samples of mung bean, kelp and pork liver were analyzed by the proposed method and inductively couple plasma-atomic emission spectroscopy (ICP-AES) method. The determination results of the two methods are in good agreement. The sampling rate is 30 samplesh(-1). | 18,969,354 |
Fluorometric enzyme immunosensing system based on a renewable immunoreaction platform for the detection of Schistosoma japonicum antibody. | A fluoroimmunosensing device which was based on ferulic acid (FA)/horseradish peroxidase system for the detection of Schistosoma japonicum antibody (SjAb) has been developed. To circumvent the difficulty of regeneration of immunocomposite surface, a natural chitosan-epoxy resin matrix was used for the immobilization of SjAg. The surface of the immunocomposite layer reacted was easily regenerated by simple polishing. The renewed surface served as a platform for the competitive immuno-reaction of HRP-SjAb and SjAb with SjAg immobilized at the support body surface and for enzymatic reaction. A novel fluorescent substrate ferulic acid for HRP, which is relatively stable toward H(2)O(2), has been adapted in the proposed fluorometric enzyme immunosensing system. FA can been catalyzed to produce a non-fluorescent species. The amount of HRP-SjAb bound to the aforementioned renewable surface layer, which is related to the content of SjAb in samples could be quantitized by measuring the decrease of fluorescence of FA induced by HRP-SjAb. The chitosan incorporated in matrix is favorable for the amplification of this sensing system due to the electrostatic reaction with FA. The proposed method showed a linear response ranging from 45 to 150ngml(-1), with an improved detection limit of 45ngml(-1). The method has been employed to determine SjAb in serum samples. | 18,969,356 |
An intelligent flow analyser for the in-line concentration, speciation and monitoring of metals at trace levels. | An intelligent and versatile flow system is proposed for the in-line speciation and/or concentration of metal ions at a wide range of concentrations without requiring manifold reconfiguration. On one hand, sample enrichment strategies are accomplished using packed-bed reactors, on the other hand speciation procedures are readily performed exploiting the selective complexation of the different oxidation states with the appropriate chromogenic reagents. The potentials of the automated methodology were evaluated using the spectrophotometric monitoring of iron as a model of chemistry. Under the optimised physical and chemical variables, linear analytical curves over the ranges 0.025-0.5 or 2.0-40mgl(-1) Fe were attained. The 3sigma detection limit, the repeatability at the 0.5mgl(-1) level, the enrichment factor for a sampling volume of 10ml, and the maximum injection throughput were 8.4ngml(-1) Fe, 2.5%, 58.6 and 22h(-1), respectively. The flowing system was applied to the speciation analysis of iron in waters, pharmaceutical formulations and agricultural products, using ICP-OES detection as an external reference method for total iron determination. A remarkable feature of the expert system hereby presented is the ability to decide by itself if the pre-concentration and/or oxidation of the sample zone is required. | 18,969,376 |
Arsenic speciation patterns in freshwater fish. | Muscle of 16 freshwater fish (9 different species belonging to 4 different families) was analysed for arsenic species using HPLC separation (anion and cation exchange) followed by on-line UV-decomposition, hydride generation and AFS detection. The main arsenic compounds found in the extracts were arsenobetaine (AsB), which accounted for 92-100% of extractable arsenic in species of salmonids (Salmo marmoratus, Oncorhynchus mykiss, Salmo trutta m. fario), and dimethylarsinic acid (DMAA), which accounted for 75% of extractable arsenic in burbot (Lota lota). AsB was also found in lower concentrations in almost all other fish species analysed (Silurus glanis, L. lota, Barbus barbus, Rutilus pigus virgo, Chondrostoma nasus). Arsenite (As(III)) and trimethylarsine oxide (TMAO) were detected in low concentrations in some representatives of Cyprinidae only (R. pigus virgo, C. nasus). Except in salmonids, an unknown cationic compound was present in most of the samples in relatively low concentrations. Cluster analysis of the generated data seems to indicate that there is a correlation between fish family and the arsenic speciation pattern. This is especially clear for the salmonids which show a completely separate cluster and thus a very distinct arsenic speciation pattern. | 18,969,382 |
Second derivative spectrophotometric method for simultaneous determination of cobalt, nickel and iron using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol. | A simple, sensitive and rapid derivative spectrophotometric method using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) has been developed for simultaneous determination of Co(II), Ni(II) and Fe(II) which have very similar chemical behavior and appear together in many real samples. The complexes of all these metal ions with 5-Br-PADAP were formed immediately at pH 7.0 ammonium acetate buffered solution and were stable for at least 24h. Second derivative spectra were selected for evaluation, because working wavelength determination was more precise and spectral overlap was less than in the ordinary and first derivative spectra. Three wavelengths at which the complexes exhibit extremum (2)D values for Co(II), Ni(II) and Fe(II) were selected as analytical wavelengths, i.e., 640, 600 and 740nm, respectively. Calibration curves drawn with zero-to-peak values at mentioned wavelengths were linear between 80 and 2000ngml(-1) for each metal ion. Concentrations of Co(II) and Ni(II) were calculated from the total (2)D values and the sum of the linear equations for these three cations at 640 and 600nm, after Fe(II) assay by making use of the (2)D value at 740nm. Limits of detection (LOD) for Co(II), Ni(II) and Fe(II) were 2.7, 13.9 and 3.0ngml(-1), respectively. The method has been applied to tool steel and heater resistance wire samples successfully. | 18,969,387 |
Fluorescence detection of cytosine/guanine transversion based on a hydrogen bond forming ligand. | In combination with abasic site (AP site)-containing oligodeoxynucleotides (ODNs), we demonstrate potential use of a hydrogen bond forming ligand, 2-amino-7-methyl-1,8-naphthyridine (AMND), for the fluorescence detection of the cytosine (C)/guanine (G) mutation sequence of the cancer repression gene p53. Our method is based on construction of the AP site in ODN duplexes, which allows small synthetic ligands to bind to target nucleobases accompanied by fluorescence signaling: an AP site-containing ODN is hybridized with a target ODN so as to place the AP site toward a target nucleobase, by which hydrophobic microenvironments are provided for ligands to recognize target nucleobases through hydrogen-bonding. In 10mM sodium cacodylate buffer solutions (pH, 7.0) containing 100mM NaCl and 1.0mM EDTA, AMND is found to strongly bind to C (K(d)=1.5x10(-6)M) in the target ODN while the binding affinity for G is relatively moderate (K(d)=50x10(-6)M). Significant fluorescence quenching of AMND is observed only when binding to C, making it possible to judge the C/G transversion with the naked eye. | 18,969,416 |
Spectrophotometric flow-injection determination of zinc in plant digests based on a spot test. | A spot test was implemented in a flow-injection system for the spectrophotometric determination of zinc in digests of plant materials. It is based on the influence of Zn(2+) on the oxidation rate of 1-naphthylethylenediamine (NED) by hexacyanoferrate(III) under acidic conditions. In order to control the precipitate formation and to maintain the resulting suspension, a micellar medium was established by adding Triton X-100. The proposed system handles about 65 samples per hour, meaning 72mug NED and 9.0mg K(3)[Fe(CN)(6)] per determination. Baseline drift is usually <0.01 absorbance per hour and the analytical signals for 0.5-2.5mgl(-1) Zn range within ca. 0.07-0.45 absorbance. Linearity of the analytical curve is fair (r>0.999, n=6) and detection limit was estimated as 0.2mgl(-1) Zn. Results are precise (R.S.D.<1%, n=10) and in agreement with flame atomic absorption spectrometry and with certified values of standard reference materials. | 18,969,424 |
Threshold bootstrap target factor analysis study of neodymium with pyridine 2,4 dicarboxylic acid N-oxide-an investigation of traceability. | Threshold bootstrap computer-assisted target factor analysis (TB CAT) has been applied to the evaluation of UV-Vis spectra of Nd(III) in aqueous solutions containing varying amounts of pyridine 2,4-dicarboxylic acid N-oxide (dipyr NO). Using the total uncertainty budget concept, probability distributions of the conditional formation constant(s) of the respective Nd(III) dipyr NO species have been evaluated. The experimental data are compatible with two different systems: a single Nd(III) dipyr NO species with logbeta(11)=2.8+/-0.11or, alternatively, a two species system with logbeta(11)=3.7+/-0.35and logbeta(12)=5.2+/-0.8. The results seem to favor the single species interpretation. However, a discussion of the influence of spectral correlation indicates that the situation should be considered with caution. The results are compared to a previous TB CAT study on Nd(III) picolinic acid N-oxide interaction illustrating the advantage of arguing in terms of probability density functions. The pyridine N-oxides with substituted carboxylic acids are structurally poorly investigated. Hence, this study calls for more structural information on rare earth pyridine N-oxide derivates. | 18,969,430 |
Electroanalytical method of TCPP and its supramolecular system with cyclodextrins. | In this paper, electroanalytical method of tetrakis (4-carboxylphenyl) porphyrin (TCPP) has been established. In a supporting electrolyte of KH(2)PO(4)-Na(2)HPO(4) (pH 7.0), a sensitive second derivative reduction peak of TCPP was found by single-sweep oscillopolarography. The potential peak is -0.70V (versus SCE).The relationship between peak height and the concentration of TCPP is linear from 1x10(-7) to 2x10(-5)moll(-1), the relative standard deviation (R.S.D.) was 0.41% (n=8), and the recovery of TCPP varied from 95.8-105.4%.The interaction of cyclodextrins (CD) with TCPP in NH(3)-NH(4)Cl (pH 8.0) has been studied by polarography. The TCPP can form the 1:1 inclusion complex with beta-CD, gamma-CD, hydroxylpropyl-beta-CD, sulfurbutylether-beta-CD and trimethyl-beta-CD. "Current method" has been used to determine the formation constants of TCPP with five CDs. The result shows that the inclusion ability of hydroxylpropyl-beta-CD is very strong. Moreover, modified beta-CD has stronger inclusion capacity than native beta-CD. The formation constant of TCPP with gamma-CD is much greater than that of TCPP with beta-CD, because the gamma-CD has a bigger cavity that can match with the size of the meso-phenyl of TCPP. The supramolecular data will provide useful information for further application of TCPP. | 18,969,472 |
Validation of the thermodynamic model of inorganic arsenic in non polluted river waters of the Basque country (Spain). | The thermodynamic model of inorganic arsenic was validated by comparing the predicted As(III) concentration with the experimentally determined one in several river waters samples of the Basque Country (Spain) collected in two sampling campaigns: spring and autumn 2000. This model takes into account the acid-base equilibria of As(III) and As(V) together with the redox equilibria between the H(3)AsO(3) and H(3)AsO(4) species. A correct prediction of As(III) concentration requires the knowledge of the total concentration of arsenic, pH, redox potential (referred to hydrogen electrode), and ionic strength values of the solution. The estimation of the activity coefficients of the arsenic species was performed by means of the Modified Bromley's Methodology (MBM). In order to perform the experimental As(III) determination, an analytical method was implemented by using an ion exchange separation of As(III)/As(V) on a continuous FIA-IE-HG-AAS system. The total arsenic concentration was determined together with total concentration of the main alkaline or alkaline-earth metals and anions in the natural waters. Temperature compensated measurements of the pH and redox potentials were made in-situ at the sampling sites. For both seasonal campaigns, the agreement between predicted and experimental As(III) is really high for those samples belonging to non polluted river waters. | 18,969,487 |
Fluorescence and terbium-sensitised luminescence determination of garenoxacin in human urine and serum. | Fluorescence and terbium-sensitised luminescence properties of new quinolone garenoxacin have been studied. The fluorimetric method allows the determination of 0.060-0.600mugml(-1) of garenoxacin in aqueous solution containing HCl/KCl buffer (pH 1.5) with lambda(exc)=282nm and lambda(em)=421nm. Micellar-enhanced fluorescence was also studied, leading to a higher than 400% increase in analytical signal in presence of 12mM sodium dodecyl sulphate (SDS), allowing the determination of 0.020-0.750mugml(-1) of garenoxacin. The terbium-sensitised luminescence method allows the determination of 0.100-1.500mugml(-1) of garenoxacin in 12mM SDS solution containing 0.08M acetic acid/sodium acetate buffer (pH 4.1) and 7.5mM Na(2)SO(3) (chemical deoxygenation agent), with lambda(exc)=281nm and lambda(em)=546nm. Relative standard deviation (R.S.D.) values for the three methods were in the range 1.0-2.0%. The proposed procedures have been applied to the determination of garenoxacin in spiked human urine and serum. | 18,969,488 |
On-line microdialysis assay of l-lactate and pyruvate in vitro and in vivo by a flow-injection system with a dual enzyme electrode. | A flow-injection biosensor system with an on-line microdialysis sampling is proposed for the simultaneous assay of l-lactate and pyruvate in serum and rat brain. The dialysate collected in the sample loop by perfusing Ringer's solution through the microdialysis probe is automatically injected into the flow-injection line with a dual enzyme electrode arranged in parallel for the flow direction. The dual enzyme electrode is constructed by hybridizing a poly(1,2-diaminobenzene) film to two sensing parts, which respond selectively to l-lactate and pyruvate, respectively, without any cross-reactivity. Both the sensing parts respond linearly to the concentrations of both analytes between 0.01 and 5mM, without any interference from oxidizable species and low-molecular weight proteins present in the dialysate. The proposed flow-injection analysis (FIA) method can be successfully applied to the simultaneous in vitro and in vivo assays of both analytes in serum and rat brain, respectively. The system can be automatically processed at an analytical speed of 19dialysatesh(-1) over a period of 5h. | 18,969,498 |
Analytical investigation of calcium oxalate films on marble monuments. | This paper describes an analytical approach to investigate the origin of oxalate films on marble. Calcium oxalate films were collected on buildings of historical importance in Lucca and Pisa (Italy) and characterised by optical microscopy (OM), scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDX), Fourier transform infrared (FTIR) spectroscopy (equipped with diamond cell), and gas chromatography-mass spectrometry (GC-MS). The morphology of the films was investigated by optical and electronic microscopy. FTIR analyses highlighted the presence of calcium oxalate (both as whewellite and weddellite), gypsum, calcite, nitrates, silicates and apatite, while EDX maps showed the distribution of elements. Several samples showed traces of organic compounds, identified by GC-MS as paraffin wax, lipids of animal origin and egg. The correlation between organic material and oxalate contents suggests the origin of the films from degradation processes of past surface treatment. | 18,969,524 |
Electroanalysis of dopamine at a gold electrode modified with N-acetylcysteine self-assembled monolayer. | Voltammetric behavior of dopamine (DA) on a gold electrode modified with the self-assembled monolayer (SAM) of N-acetylcysteine has been investigated, and one pair of well-defined redox peaks of dopamine is obtained at the SAM modified gold electrode. The oxidation peak current increases linearly with the concentration of dopamine in the range of 1.0x10 (-6)to 2.0x10 (-4)moll(-1). The detection limit is 8.0x10(-7)moll(-1). This method will be applicable to the determination of dopamine in injection of dopamine hydrochloride, and the good recovery of dopamine is obtained. Furthermore, The SAM modified gold electrode can resolve well the voltammetric responses of dopamine and ascorbic acid (AA), so it can also be applied to the determination of dopamine in the presence of ascorbic acid. | 18,969,533 |
Multiresidue determination of sulfonamides in a variety of biological matrices by supported liquid membrane with high pressure liquid chromatography-electrospray mass spectrometry detection. | A high performance liquid chromatography (HPLC) coupled to a mass spectrometer (MS) was used for a simultaneous determination of 16 sulfonamide compounds spiked in water, urine, milk, and bovine liver and kidney tissues. Supported liquid membrane (SLM) made up of 5% tri-n-octylphosphine oxide (TOPO) dissolved in hexyl amine was used as a sample clean-up and/or enrichment technique. The sulfonamides mixture was made up of 5-sulfaminouracil, sulfaguanidine, sulfamethoxazole, sulfamerazine, sulfamethizole, sulfamethazine (sulfadimidine), sulfacetamide, sulfapyridine, sulfabenzamide, sulfamethoxypyridazine, sulfamonomethoxine, sulfadimethoxine sulfasalazine, sulfaquinoxaline, sulfadiazine, and sulfathiazole. Some of these compounds, such as, sulfaquinoxaline, sulfadiazine, sulfabenzamide, sulfathiazole and sulfapyridine failed to be trapped efficiently by the same liquid membrane (5% TOPO in hexylamine). The detection limits (DL) obtained were 1.8ppb for sulfaguanidine and sulfamerazine and between 3.3 and 10ppb in bovine liver and kidney tissues for the other sulfonamides that were successfully enriched with SLM; 2.1ppb for sulfaguanidine and sulfamerazine and between 7.5 and 15ppb in cow's urine, whereas the DL values in milk were 12.4ppb for sulfaguanidine and sulfamerazine and between 16.8 and 24.3 for the other compounds that were successfully enriched by the membrane. Several factors affecting the extraction efficiency during SLM enrichment, such as donor pH, acceptor pH, enrichment time and the membrane solvent were studied. | 18,969,572 |
Electrochemistry and scanning electron microscopy of polyaniline/peroxidase-based biosensor. | An amperometric biosensor was prepared by in situ deposition of horseradish peroxidase (HRP) enzyme on a polyaniline (PANI)-doped platinum disk electrode. The PANI film was electrochemically deposited on the electrode at 100mVs(-1)/Ag-AgCl. Cyclic voltammetric characterization of the PANI film in 1M HCl showed two distinct redox peaks, which prove that the PANI film was electroactive and exhibited fast reversible electrochemistry. The surface concentration and film thickness of the adsorbed electroactive species was estimated to be 1.85x10(-7)molcm(-2) and approximately 16nm, respectively. HRP was electrostatically immobilized onto the surface of the PANI film, and voltammetry was used to monitor the electrocatalytic reduction of hydrogen peroxide under diffusion-controlled conditions. Linear responses over the concentration range 2.5x10(-4) to 5x10(-3)M were observed. Spectroelectrochemistry was used to monitor the changes in UV-vis properties of HRP, before and after the catalysis of H(2)O(2). The biosensor surface morphology was characterized by scanning electron microscopy (SEM) using PANI-doped screen-printed carbon electrodes (SPCEs) in the presence and absence of (i) peroxidase and (ii) peroxide. The SEM images showed clear modifications of the conducting film surface structure when doped with HRP, as well as the effect of hydrogen peroxide on the morphology of biosensor. | 18,969,575 |
The separation and determination of nitrophenol isomers by high-performance capillary zone electrophoresis. | o-Nitrophenol, m-nitrophenol, and p-nitrophenol could well be separated by capillary zone electrophoresis (CZE) by only adjusting the run buffer with methanol. Efficiency up to 10(5) theoretical plates per meter was achieved. The effects of several important factors were investigated to find optimum conditions. The linear range, regression equation, and the recovery were given. This method possessed the advantages of simplicity, rapidity, and good reproducibility; it can be developed for the separation of practical samples in environment analysis. | 18,969,578 |
Macrocyclic antibiotics as chiral selectors in the design of enantioselective, potentiometric membrane electrodes for the determination of l- and d-enantiomers of methotrexate. | Three enantioselective, potentiometric membrane electrodes (EPMEs) based on macrocyclic glycopeptide antibiotics-vancomycin and teicoplanin (modified or not with acetonitrile)-were proposed for the determination of l- and d-enantiomers of methotrexate (Mtx). The linear concentration ranges for the proposed enantioselective membrane electrodes were between 10(-6) and 10(-3)moll(-1) for l- and d- methotrexate. The slopes of the electrodes were 58.00mV/pl-Mtx for vancomycin-based electrode; 57.60mV/pd-Mtx for teicoplanin-based electrode and 55.40mV/pd-Mtx for teicoplanin modified with acetonitrile-based electrode. The detection limits of the proposed electrodes were of 10(-8)moll(-1) magnitude order. The surfaces of the electrodes are stable and easily renewable by polishing on alumina paper. All proposed electrodes proved to be successful for the determination of the enantiopurity of Mtx as raw material and of its pharmaceutical formulations (tablets and injections). | 18,969,580 |
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