title stringlengths 0 1.13k | abstract stringlengths 1 15.7k | PMID int64 22 36.5M |
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A practical approach to high performance capillary electrophoresis with biosynthetic human growth hormone as a model protein. | Biosynthetic human Growth Hormone (B-hGH) is a protein comprising 191 amino acids. The molecular weight is 22,125 and the isoelectric point is close to pH 5. Due to the ready availability of closely related analogues B-hGH was used as a model protein thus allowing for the demonstration and evaluation of the high resolution capability of high performance capillary electrophoresis (HPCE). The same apparatus was used throughout the experiments and an optimum signal-to-noise ratio was found at 200 nm. Linearity was observed between peak area, retention time and the hGH concentration or sample introduction time. Baseline separation of hGH, desamido hGH and didesamido hGH was obtained. Examples showing analysis with 1 million theoretical plates per meter, high speed separation, simultaneous analysis of multiple samples, sample stacking, hGH tryptic digest, and hGH lysate are reported. The use of electrophoretic velocities instead of apparent velocities for peak identification is illustrated. | 18,965,311 |
Adsorbing colloid flotation separation and polarographic determination of Mo(VI) in water. | A method is described for the flotation and determination of Mo(VI) in water at ng/ml levels. Mo(VI) is preconcentrated and separated by adsorbing colloid flotation employing aluminium(III) hydroxide as collector and sodium lauryl sulphate as surfactant at pH 5.3 +/- 0.1. The molybdenum content in the froth is estimated by using the catalytic wave of Mo(VI) in the presence of nitrate by charging current compensated d.c. polarography (CCCDCP) or differential pulse polarography (DPP). The effect of variables such as pH, ionic strength, concentration of collector and surfactant, time of stirring and gas flow-rate on the recovery of Mo by flotation is reported. The effects of various cations and anions on the flotation and determination of Mo are studied. This method is employed for the determination of molybdenum in natural fresh water samples. | 18,965,320 |
Polarographic determination of atmospheric nitrogen oxides. | A new polarographic method is described for the determination of nitrite/nitrogen oxides. The nitrite is first diazotized with p-aminobenzoic acid, followed by coupling to 8-hydroxyquinoline to produce an azo dye. This azo dye is adsorbable on a mercury drop electrode and its reduction is reversible. The linear response range is 6 x 10(-9)-3 x 10(-7) g/ml. The detection limit is 4 x 10(-9) g/ml. This method has been applied to the determination of nitrogen oxides in the air. | 18,965,350 |
Decomposition of Cu(PCD)(2) extracted into IBMK and DIBK phases from hydrochloric acid media. | The decomposition of the bis(1-pyrrolidinedithiocarbamato) copper(II) complex [Cu(PCD)(2)] extracted into isobutyl methyl ketone (IBMK) and di-isobutyl ketone (DIBK) from hydrochloric acid solution (0.01-8M) has been studied with UV-visible and ESR spectrometry. The mixed-ligand complex CuCl(PCD) is formed as an intermediate and CuCl(2) or CuCl3(-)(3), are formed as final products, in the decomposition of Cu(PCD)(2). The concentration of free hydrochloric acid dissolved in the extract has also been determined, and the effect of the free acid on the decomposition has been studied. The decomposition reaction of Cu(PCD)(2) extracted from hydrochloric acid solution can be thought of as a ligand substitution by Cl(-), and occurs with both IBMK and DIBK extraction. | 18,965,358 |
A selective spectrophotometric method for determination of quercetin in the presence of other flavonoids. | A simple, rapid and highly selective method for determination of quercetin in the presence of other flavonoids was developed. The method is based on the oxidation reaction of quercetin in neutral aqueous solution with N-bromosuccinimide (NBS) in the presence of phenol to give a violet chromogen measurable at 510 nm. Beer's law was valid within a concentration range of 2.5-30 mug/ml with a good correlation coefficient (r = 0.9990). All variables were studied to optimize the reaction conditions. The method is highly selective for quercetin. Other investigated flavonoids do not interfere. Mixtures of flavonoids were also analysed through native UV measurements of absorbance readings at 370 nm and then at 510 mn after adopting the proposed procedure. The method could also be utilized for the quantitative determination of quercetin in some plant extracts. Moreover, the proposed procedure could be considered as a good tool to follow the hydrolysis of quercetin glycosides. | 18,965,372 |
Flow-injection coulometric titrations. | A flow-injection analysis technique based on stop flow coulometric titrations is described, utilizing a gradient chamber, reagent generation chamber, and detector flow cell integrated into a single unit. The use of stop flow allowed for automated sample dilution up to a factor of 100 times. The system has been used to titrate samples of sodium hydroxide in the range 5 x 10(-4)-4M, and nitric acid ranging from 5 x 10(-3)-15M. Analyses over the entire range of concentrations yielded a relative standard deviation of less than 3%. A correlation coefficient of 0.999 was obtained for all comparisons with manual titrations. Remote spectrophotometric detection was performed with optical fibers. No frit or membrane is required to separate the generating and counter electrodes within the system, yet the advantages of conventional coulometric titration, which eliminate the problems of reagent and calibration solution handling, storage or degradation, are retained. | 18,965,376 |
Spectrophotometric method for determination of sulfide with iron(III) and nitrilotriacetic acid by flow injection. | A manual colorimetric method for determination of sulfide has been adapted to flow injection, systematically optimized, and more fully characterized. Its intended application is for measurement of sodium sulfide reagent strength in pulp process streams, and sulfide contamination in effluent from Kraft pulp mills. In the flow-injection method developed, a sample solution containing sulfide is reacted with a mixture of iron(III) and nitrilotriacetic acid under ammoniacal conditions. The absorbance of the intensely-colored green product of this reaction is measured at 636 nm. Excess sulfite is present as a color stabilizer. A linear dynamic range of 20-100 ppm sulfide is readily achieved; the relative standard deviation is less than 1.2% (n = 10) throughout this range, and 0.37% (n = 10) midrange at 60 ppm. The usable dynamic range is 8-250 ppm sulfide. Long-term stability of the method is ensured by periodically performing an automatic cleaning cycle using a hydrochloric acid wash solution. This prevents tube discoloration and removes any precipitates which are formed under strongly alkaline conditions. The sample throuhput rate is at least 30/hr, given alternate acid wash cycles. | 18,965,378 |
Electrochemically-controlled generation of small amounts of carbon monoxide. | The generation of carbon monoxide is based on oxidation of carbon at a temperature of 920-950 degrees by electrolytically generated oxygen. The rate of production of CO is a linear function of the oxygen generating current over a range of 5-60 mA and corresponds to the theoretical value. By the method described it is possible to obtain CO concentrations from 0.0075 to 2.5% in an inert gas (nitrogen, argon and helium). | 18,965,389 |
Voltammetric determination of mercury(II) at a carbon paste electrode in aqueous solutions containing tetraphenylborate ion. | The determination of mercury(II) ions can be achieved by monitoring the decrease in the oxidation peak of the tetraphenylborate ion in the presence of this metal ion at a carbon paste electrode. The reaction between mercury(II) and the tetraphenylborate ion results in the formation of diphenylmercury, thus providing the method with good selectivity over other metal ions. Using anodic stripping voltammetry in a neutral electrolyte, a linear dependence of the decrease of peak height was observed on increasing the mercury(II) concentration in the range 1 x 10(-6)-8 x 10(-9)M mercury(II). Zinc(II), cadmium(II), lead(II), nickel(II), cobalt(II), tin(II), potassium(I) and ammonium(I) ions did not interfere at a 1000-fold concentration excess. Iron(III) and chromium(III) did not interfere at a 250-fold and 50-fold concentration excess, respectively. Following masking procedures, copper(II), bismuth(III) and silver(I) did not interfere at a 100-fold concentration excess. The method can be used to determine the concentration of mercury(II) in natural waters contaminated by this metal. | 18,965,392 |
Optimization of atomic fluorescence measurements with a microcomputer-based time-multiplex multiple-slit spectrometer. | An automated multielement flame atomic fluorescence (AF) spectrometer is described. The instrument employs a multiple exit slit monochromator and a single detector. Each element is excited to fluoresce with a single-element hollow cathode lamp (HCL) and a time-multiplex mode is used for pulsing the HCLs and gated data acquisition. A microcomputer controls the pulsing of HCLs, sample introduction into the flame and data acquisition. Optimization of the HCL pulse width and peak current is shown to be critical. With an air/H(2) flame sheathed with Ar, the following single-element detection limits (in mug/ml) were obtained: Au, 0.2; Cd, 0.005; Co, 0.03; Cu, 0.003; Fe, 0.05; Mg, 0.0008; Mn, 0.007; Ni, 0.04; Pb, 1 and Zn, 0.02. Some multielement detection limits were a factor of 2-5 worse. At higher analyte concentrations, the signal to noise ratio decreased due to an increase in the relative analyte fluorescence flicker noise. | 18,965,446 |
Oscillopolarographic adsorptive wave determination of microamounts of orthophosphate. | In the system HCl-Sb(III)-ammonium molybdate-acetone-butanone, PO(3-)(4), Sb(III) and Mo(VI) form a ternary heteropoly acid, which can be adsorbed on a dropping mercury electrode and reduced to a heteropoly blue. The electrochemical reaction produces a sensitive polarographic wave with peak potential of -0.42 V vs. SCE. The limit of determination of phosphate is 6 x 10(-8)M. The coefficients of variance are 10 and 3% for 0.1 and 1muM phosphate, respectively. | 18,965,448 |
Capillary gas chromatography of hydrocarbon mixtures containing alkanes and alkenes, selective olefin stripping applied to very diluted samples. | An original subtraction method was developed to distinguish between alkanes and alkenes in a complex hydrocarbon mixture. The method described is very fast, inexpensive and requires only 100-200 mul of sample. Its steps include bromination of the olefins and adsorption on a silica gel column followed by gas chromatography. Examples are presented to demonstrate the applicability of the method in practice. The results are compared with those obtained from catalytic hydrogenation. | 18,965,449 |
Extraction mechanism of monovalent ion-pairs by polyurethane foams. | The extractability sequence of K(+) approximately Rb(+) > Cs(+) > Na(+) > Li(+) for the extraction with polyether foam suggests that the cation chelation mechanism might be operative. However, the same order was obtained for the extraction with 100% polypropylene oxide polyether foam which does not normally adopt a helical structure to form oxygen-rich cavities as easily or as effectively as polyethylene oxide to accommodate alkali metal ions. This result indicates that a hole-size/cation-diameter relationship may not be required for the high extraction of K(+). The extraction of alkali metal DPAs and hydroxides from methanol demonstrates the importance of the solvent effect. It indicates that the water-structure enforced ion-pairing (WSEIP) is the driving force for extraction of the ion-pairs. The extraction mechanism for ionic species can be described as an ion-pair extraction process. The overall effect of ion-pair formation in water and interaction of the extracted ions with foam appears to determine the extractability of the ions of the extractable ion-pair. | 18,965,459 |
Electrochemical study of solvent extraction with 8-quinolinols as complexing agent-I. Distribution behavior of 8-quinolinols. | The distribution behavior of 8-quinolinols (HQ) in organic and acidic aqueous solutions (or alkaline solutions) was electrochemically examined by current scan polarography and chronopotentiometry. It follows from the results that the half wave potential of the observed polarographic waves, corresponding to the Faradaic transfer of quinolinolium ions (or oxinate ions) formed in the aqueous solution after distribution of quinolinols is dependent on the dissociation constant of H(2)Q(+) (or HQ) and the pH of the aqueous solution, but independent of the distribution constant of 8-quinolinols. | 18,965,472 |
Determination of sulfide with chloranilic acid by biamperometric and automatic potentiometric end-point detection with a lead chloranilate selective electrode. | A titrimetric method for determination of sulfide and of sulphur in steels with chloranilic acid by biamperometric and automatic potentiometric end-point detection is described. The construction of the sensor for potentiometric indication is also described. The results obtained agree with those of the iodine-thiosulfate method and with the certified values for the steels. | 18,965,487 |
Study of the transport of silver across a supported liquid membrane containing sulphide podand. | The transport of silver through a supported liquid membrane saturated with a polydentate neutral ionophore 1,12-di-thienyl-2,5,8,11-tetrathiadodecane in m-chlorotoluene has been studied. Thiosulphate was used as the stripping solution. The influence of the feed solution composition, the type of a microporous polypropylene Celgard support, the ratio of feed/receiving solution volume, and the initial Ag concentration on the rate of transport of silver was examined. Transport of Ag is selective towards Cu(II), Pb and Zn, but these cations affected the rate of the Ag flux. | 18,965,491 |
Analytical and mechanistic aspects of the room-temperature fluorescence and phosphorescence of benzo(f)quinoline adsorbed on silica gel chromatoplates with humidified gases. | The solid-matrix room-temperature fluorescence and room-temperature phosphorescence properties of benzo(f)quinoline adsorbed on silica gel chromatoplates were investigated over a wide range of humidities in N(2), air and O(2). Both neutral and acidic conditions were used and even at the highest relative humidity used, 93% relative humidity, the room-temperature fluorescence and phosphorescence intensities from benzo(f)quinoline were not totally quenched. However, in all experiments, the room-temperature phosphorescence was much more sensitive to humidity quenching than the room-temperature fluorescence. The results gave rather detailed information on quenching of the room-temperature fluorescence and phosphorescence in the different gases at a variety of humidities. It was possible to calculate the contribution to the percent decrease in luminescence due to moisture or a quenching gas. Thus, a more detailed assessment could be made about the quenching of moisture and individual quenching gases on the solid-matrix fluorescence and phosphorescence. | 18,965,496 |
Analysis of acrolein and acrylonitrile in aqueous solution by membrane introduction mass spectrometry. | Acrolein and acrylonitrile can be quantified directly at low levels in aqueous solution using membrane introduction mass spectrometry. Electron impact was used to generate positively charged ions and electron capture of the O-(2,3,4,5,6-pentafluorobenzyl)hydroxyl amine (PFBOA) derivative was used to generate negatively charged ions of acrolein in aqueous solutions. The origins of all ions in the mass spectra and product MS/MS spectra recorded using both ionization methods were assigned and a reaction scheme is given which accounts for the fragmentation of the PFBOA derivative. Detection limits were measured using multiple reaction monitoring in both the methods. With electron capture detection, acrolein could be detected without preconcentration at 10 ppb levels. Electron impact ionization and multiple reaction monitoring both allowed the measurement of acrylonitrile at levels as low as 10 ppb. | 18,965,502 |
Studies on complexation equilibria between water-soluble hydrazones which consist of 5-nitro-2-pyridylhydrazine and heterocyclic ketones and divalent metal ions. | Complexation equilibria between five water-soluble hydrazones which consist of 5-nitro-2-pyridylhydrazine and heterocyclic ketones and divalent metal ions have been studied spectrophotometrically. Equilibrium constants of the complexation reactions and overall formation constants of the resultant complexes have been determined and species of the complexes clarified. | 18,965,510 |
Atomization efficiency of a Massmann-type graphite furnace. | The atomization efficiency of the Perkin-Elmer HGA-400 for the production and containment of atomic vapour has been determined for Al, Co, Au, Ni, Fe, Ag, Ga and Cu by a method developed under non-isothermal conditions. The method takes into account the residence time and the shape of the absorbance signal profile. It is based on the entire absorption signal profile rather than on any part of it. The uncertainty in the method arises from calculation of the rate constant of atom loss due to temperature gradient which has a pronounced effect on the "effective" length of the analysis path when the atomizer is operated under non-isothermal conditions. The average value of the atomization efficiency for the eight elements used for this study was found to be about 0.10. | 18,965,519 |
Simultaneous determination of Cl(-), Br(-), I(-) and F(-) with flow-injection/ion-selective electrode systems. | Flow-through ion-selective electrodes were constructed from compressed pellets (8-10 mm thick, 13 mm diameter, 10 tons/cm(2) pressure) of Ag(2)S/AgX (X = Cl(-), Br(-) or I(-)) drilled longitudinally (1.5 mm diameter hole) to be suitable for use in flow-injection analysis. A column of AgCl (5.5 cm long, 2-3 mm i.d.) was included in the Cl(-)-electrode manifold to remove interferences from 10(-4)M Br(-) and 3 x 10(-5)M I(-) and S(2-). A column of amalgamated lead (2-3 cm long, 2-3 mm i.d.) was used in the Br(-) electrode manifold to remove interference from 2 x 10(-5)M I(-), 3 x 10(-5)M S(2-) and 7 x 10(-4)M Cl(-). These columns and the addition of ascorbic acid were not required when I(-) was determined with the iodide electrode. The carrier stream was 0.1M sodium perchlorate (pH 4) at a flow-rate of 0.5 ml/min. The sample pH could be 4-7. Simultaneous determination of Cl(-) and I(-), Cl(-), I(-) and Br(-) and Cl(-), I(-), Br(-) and F(-) ions was possible with combinations of the corresponding electrodes and columns in series and/or parallel in specially designed manifolds. Calibration plots were linear, with almost theoretical slopes, down to 10(-6)M I(-), 5 x 10(-6)M Br(-), 10(-4)M Cl(-) and 5 x 10(-6)M F(-), with precision better than 1%. Sampling rates for single-ion determinations were 72, 102, 90 and 80 per hr for the one-, two-, three- and four-electrode systems respectively. Determinations of these ions in water samples by the recommended procedure and by established batch methods showed no significant difference at the 95% confidence limits in a paired comparison t-test. | 18,965,525 |
Preparation and application of selenite ion selective electrode. | A new selenite ion selective electrode using 4,6-dibromopiaselenole as active material, PVC as membrane matrix and dibutyl phthalate as plasticizer has been developed. An analytically useful potential change occurs from about 10(-6)-10(-1)M Se(IV), and the slope of the linear portion is -23.6 mV/10-fold change in Se(IV) concentration at a temperature of 21 degrees . The electrode shows fairly good selectivity for selenite ion over other anions and has been used for the successful determination of total selenium in human hair. | 18,965,526 |
Rapid sequential determination of inorganic mercury and methylmercury in natural waters by flow injection-cold vapour-atomic fluorescence spectrometry. | A novel method for the rapid sequential determination of inorganic mercury and methylmercury in natural waters at the ng/l. level has been developed. Trace enrichment and separation of mercury species are achieved using a microcolumn of sulphydryl cotton which has a relatively high affinity for methylmercury. The limit of detection for methylmercury based on processing of a 0.5-ml sample volume was 6 ng/l. Application to river waters is demonstrated. | 18,965,566 |
Phase composition analysis of hydrous aluminium oxides by thermal analysis and infrared spectrometry. | A general method for determination of the phase composition of hydrous aluminium oxides by thermal analysis and infrared spectrometry, and determination of the transformation temperature of mixtures of Al(OH)(3) and AlOOH into alpha-Al(2)O(3) are described. | 18,965,574 |
Optimal design of diffusive samplers. | Some commercially available diffusive samplers use two layers of adsorbent placed in series. After sampling is completed, the time weighted average concentration of analyte is estimated from the weighted sum of the uptake of analyte on these two layers. It is known that such a division into layers can increase the permissible sampling time. Here the principles underlying this sampling procedure are analyzed through a fundamental application of the theory of diffusion. Using a trial and error procedure, the optimal division of adsorbent was calculated, and the increase in sampling time that such a division can give was confirmed theoretically. Also, should the uptake in the backup layer exceed a predetermined fraction of the total uptake, this will indicate misuse of the diffusive sampler. | 18,965,607 |
Rapid gas analyses for the investigation of spontaneous combustion using capillary gas chromatography. | A simple and fast but sensitive and precise gas chromatographic method is described for the quantitative determination of O(2), N(2), CO, CO(2), C1 and C2-hydrocarbons for coal research. Gas analyses are necessary to obtain parameters for modelling spontaneous combustion and to predict long term coal behaviour. The method is based on a single PLOT-type capillary column in a single channel gas chromatograph. Using a micro-volume TCD coupled in series with a FID detector containing a capillary methanizer it is possible to determine high and trace level gases simultaneously. Trace quantities of CO and CO(2) can be determined with a single analysis and the detection limits are improved significantly using the capillary methanizer. The detection limit of the described method is approximately ten parts per million CO(2) and one part per million CO. Using the same instrument configuration the O(2)/N(2) ratios (major components), as parameter for coal reactivity, are also determined. The proposed approach is restricted to the determination of gases evolved during coal studies and the application to other gas mixtures is not considered. | 18,965,618 |
Determination of chlorinated hydrocarbons introduced into air/acetylene flames by Fourier transform infrared emission spectroscopy. | A Fourier transform spectrometer is used to record the infrared emission from chlorinated hydrocarbons combusted in an air/acetylene flame. In this manner, the chlorinated hydrocarbons are determined by monitoring the infrared emission of hydrogen chloride at 2653 cm(-1). Discussion is presented of the air/acetylene flame background, and the potential spectral interference from the emission of deuterated species. Practical detection limits for chloroform, carbon tetrachloride and methylene chloride in acetone, methanol, and ethanol are solvent independent and are found to be 1.1, 0.80, and 1.0%, respectively. Calibration curves for these three analytes are linear from their detection limits to approximately 55% (v/v). In addition, evidence is presented that flame flicker-noise does not lead to a multiplex disadvantage when the Fourier transform instrument is used for data acquisition. | 18,965,624 |
The determination of organotin compounds in edible oils by gas chromatography-atomic absorption spectrometry. | An extraction method for butyl-, cyclohexyl-, octyl- and phenyltin compounds from edible oils was developed using 0.05% tropolone in 0.04M HCl/methanol. Cooling the methanol extracts in a dry ice/methanol bath removed approximately 64% of nonvolatile coextractives without affecting recoveries. Methyl derivatives formed by Grignard reaction were quantitated by gas chromatography-atomic absorption spectrometry. Edible oils sold in poly(vinyl chloride) containers had ng/g levels of dioctyl- and monooctyltin. GCMS confirmed the presence of octyltin and did not detect any other organotin compounds in the extracts. | 18,965,630 |
A new method for the evaluation of the oxidizing equivalent of manganese in surface freshwaters. | The suitability of application of a number of previously used methods for the evaluation of the oxidizing equivalent (OE) of manganese in natural waters is compared with a new method, which depends upon colour development of the dye N,N'-diethyl-p-phenylenediamine (DPD) upon oxidation by oxidized forms of manganese. The effect of introducing a commonly used metabolic poison, azide, into the most reliable of these determinations of OE has also been assessed. | 18,965,662 |
Flow injection method for the assay of the anti-arrhythmic procainamide HCl in drug formulations utilizing statistical optimization techniques. | A flow injection spectrophotometric method for the determination of procainamide HCl was explored. The method was based on the oxidation of procainamide HCl with cerium(IV) in sulphuric acid media and subsequent monitoring of the absorbance of the oxidized form of the drug at 480 nm. A sample rate of 250 samples per hour was attained. The procedure was optimized by the Factorial Design at two upper and lower levels of the five parameters sample loop size, flow rate, coil length, sulphuric acid and cerium(IV) concentrations. The latter three indicated high interactions and revealed significance to peak height value therefore optimized by the Super Modified Simplex programme. The optimized FI system with a linear calibration range of 100-600 ppm was found to be adequate and suitable for determination of procainamide HCl in proprietary drugs. A high degree of accuracy of the results was demonstrated by a statistical comparison with those obtained by the British Pharmacopoeia method of the same batch of drugs. | 18,965,675 |
Direct flame atomic absorption spectrophotometric determination of Mn in rocks, nodules, soils and related materials using tartaric acidKClSrCl(2) mixture. | A mixture of tartaric acid-potassium chloride and strontium chloride has been used for accurate and precise estimation of manganese in various international reference rocks, nodules, soil and related samples by flame atomic absorption spectrophotometry (FAAS). The method is fairly rapid and involves no separation of the analyte from the matrix elements. Sample decomposition is straight-forward (2:1 mixture of hydrogen fluoride and perchloric acid). Forty-seven well characterized standard reference samples of diverse matrices have been analysed and the results are compared with the reported data. | 18,965,690 |
Spectrophotometric determination of chromium with Iodonitrotetrazolium chloride and Tetrazolium Violet. | The interaction of Iodonitrotetrazolium chloride and Tetrazolium Violet with chromium(VI) has been studied and the formation of ion-associates with a 1:1 composition in hydrochloric acid medium established. Extraction photometric methods for determination of chromium in steels and soils have been developed. | 18,965,691 |
JESS, a joint expert speciation system-III. Surrogate functions. | A new, general method of coupling calculations of equilibria with those of other chemical effects and processes is described. The method, based on the use of simple empirical functions, is demonstrated by applying it to changes of ionic strength and temperature in speciation modelling. | 18,965,712 |
Assignment of standard pH values [pH*(s)] to buffers in 50 mass % methanol + water from 288.15 to 308.15 K. | The secondary dissociation constants of o-phthalic and phosphoric acids have been determined in methanol + water (50 mass %) from reversible e.m.f. measurements of the cell of the type: Pt, H(2)(1 atm)|M(2)A(m), MHA(m), MCl|AgCl; Ag at different temperatures (288.15-308.15 K) and at different ionic strengths. To minimize the unsteadiness in potential measurements palladium coated platinum electrodes have been used. The large set of such e.m.f. values has been analyzed in terms of a multi-linear regression method recommended in recent IUPAC documents. The thermodynamic values DeltaG degrees , DeltaH degrees and DeltaS degrees , for the respective equilibria, were estimated. Standard pH values [pH*(s)] have been assigned to buffers in methanol + water (50 mass %) at temperatures between 288.15 and 308.15 K. | 18,965,719 |
Resin phase spectrophotometry of beryllium by an optical fiber and beryllon II. | We have developed a resin phase spectrophotometric method to determine the amount of beryllium by detecting a change in absorbance of the resin phase. 8-Hydroxynaphthalene-3,6-disulphonic acid-(1-azo-2')-1',8'-dihydroxynaphthalene-3',6'-disulphonic acid tetrasodium salt (beryllon II) immobilized by a strong base anion-exchange resin on the end of a bifurcated optical fiber bundle was chosen as a material sensitive to beryllium. Experiments were made using a home-made optical fiber spectrophotometer. The properties of the resin phase proved to be good for continual use of 350 times during a month. The reaction order between immobilized beryllon II and beryllium in solution was determined by kinetic theory and experiments. This method was also used to determine the amount of beryllium in beryllium-copper alloy; the response was linear from 0.43 to 2.60 mug/ml at pH 12.5 and 676 nm. The effect of interfering ions on the determination of beryllium was studied at the same time. | 18,965,722 |
Difference spectrophotometric assay of benzaldehyde in benzyl alcohol. | A simple and rapid procedure is described for the selective determination of benzaldehyde in benzyl alcohol intended for use in the manufacture of parenteral dosage form. The assay is based upon the measurement of the difference absorbance between two equimolar solutions of benzaldehyde in buffer solution pH 5.75, one of which also contains sodium bisulphite. The difference absorbance which has a maximum at 248 nm is due to the different spectral characteristics of benzaldehyde and its adduct form with sodium bisulphite is proportional to concentration of benzaldehyde. The accuracy, precision, sensitivity and specificity of the procedure are discussed. Application of the assay is described for different batches of benzyl alcohol. The results are compared with the official (BP) GLC method. | 18,965,728 |
Responses of H(+) selective solvent polymeric membrane electrodes fabricated from modified PVC membranes. | Potentiometric responses of a novel class of pH sensitive ionophores, namely several phenoxazine derivatives, were tested in different modified PVC matrices. The ionophores were compounded into liquid membranes as usual or were covalently coupled to the polymeric matrix. The general analytical performance of the membranes and other membrane characteristics (i.e., resistance and response time, as measures of membrane decomposition or structural changes) were followed in time. The transient responses of membranes with mobile ionophores in high molecular weight (HMW) and carboxylated PVC (PVC-COOH) were compared to those with immobilized ionophores. The response time of membranes with immobilized ionophores was found to be between those with mobile ionophores in HMW (fast response) and PVC-COOH (sluggish response). Accordingly, the rate of response was correlated primarily to the -COOH content of the membranes. | 18,965,733 |
Investigation of the composition of complexes and the stoichiometry of non-complex reactions by flow injection method. | Combining the Asmus straight-line method with the flow injection (FI) technique, a new FI-straight-line method is established to investigate the formulas of the blue, the purple and the red complexes formed by iron(III) and Tiron in different pH solutions. Using the proposed FI-straight-line method, the stoichiometries of cyanide and harbituric acid for producing the intermediate and the final product of the chromogenic reaction of cyanide with pyridine-barbituric acid reagent are also studied. | 18,965,734 |
Structural characterization and sequence distributions of polysiloxanes using pyrolysis MS/MS. | Novel polysiloxanes, with 4-(dialkylamino)pyridine substituents, are characterized by pyrolysis tandem mass spectrometry. These polymers form abundant cyclic oligomeric ions under both desorption electron ionization (DEI) and desorption chemical ionization (DCI) conditions. Product MS/MS spectra of the cyclic ions reveal characteristic fragmentations under low energy collision activated dissociation. Protonated cyclic oligomers higher than the pentamer are mainly due to the proton bound dimers of lower oligomeric units. The cyclic oligomers are shown to have proton affinities greater than 1000 kJ/mole. It is proposed that thermal depolymerization occurs through an intramolecular siloxane bond rearrangement, which is in agreement with a previously proposed "loop mechanism". Markovian statistical calculations are applied to the DCI mass spectral data in order to determine the sequence distribution of siloxane copolymers. Application of this method show that the monomers in the copolymers examined are non-randomly distributed. | 18,965,774 |
Determination of gallium by square-wave voltammetry anodic stripping, based on the electrocatalytic action of 2,2'-bipyridine in dimethylsulphoxide: comparison with an aqueous NaSCN/NaClO(4) electrolyte. | Deposition potential, deposition time, square-wave frequency, 2,2'-bipyridine concentration, and gallium concentration have been studied in detail, for the determination of trace concentration levels of the metal by square-wave voltammetry anodic stripping analysis, in dimethylsulphoxide. Optimum conditions have been found for gallium(III) determination and results compared to those obtained in 0.5M NaSCN + 4.2M NaClO(4) aqueous electrolyte by obtaining calibration graphs for the range 1 x 10(-8)M-1 x 10(-5)M gallium. Accuracy (+/- 3%) and precision (4-6% SD) of this method were assessed with both 4 x 10(-8)M and 4 x 10(-7)M gallium solutions used as synthetic samples. The efficiency of solvent extraction of gallium with di-isopropyl ether was found to be 99.98% at a 4 x 10(-7)M gallium concentration. The proposed method was applied to the determination of the gallium content in rock mineral samples (using the above mentioned solvent extraction procedure), are compared to those obtained with the NaSCNNaClO(4) based electrolyte. No statistically significant difference was observed. Analytical procedures followed are given in detail. | 18,965,779 |
Flow-injection fluorimetric determination of trimeprazine and trifluoperazine in pharmaceutical preparations. | A flow-injection configuration for the fluorimetric determination of trimeprazine and trifluoperazine is proposed. The procedure is based on oxidation of the drugs by cerium(IV). The fluorescence of cerium(III) formed in the oxidation of trimeprazine or trifluoperazine is monitored. Lineal calibration graphs were obtained between 2 x 10(-7) and 1 x 10(-5)M for both trimeprazine and trifluoperazine with a sampling rate of 60 samples/hr. The relative standard deviations were over the ranges 0.78-1.16 and 0.84-0.97% for trimeprazine and trifluoperazine respectively. The applicability of the method to determination of trimeprazine and trifluoperazine was demonstrated by investigating the effect of potential interferences and by analysis of commercial pharmaceutical preparations. | 18,965,791 |
Kinetic spectrophotometric determination of low levels of nitrite by catalytic reaction between pyrogallol red and bromate. | A kinetic spectrophotometric method for the determination of trace nitrite (0.003-1.000 microg/ml) based on its catalytic effect on the reaction between potassium bromate and pyrogallol red in acidic media is described. The reaction is monitored spectrophotometrically by measuring the decreasing colour of pyrogallol red at 467 nm by the fixed-time method. At a given time of 3.0 min at 30 degrees, the detection limit is 0.001 microg/ml and the relative standard deviation for 0.010 microg/ml nitrite is 1.8% (n = 8). The method is free from most interferences, especially from large amounts of nitrate and ammonium. The procedure was successfully applied to the determination of trace nitrite in natural water without preconcentration. | 18,965,793 |
Volatilization of methyl borate in iron matrix. Determination of boron in steel by ICP atomic emission spectrometry. | A rapid and reliable method for the determination of boron by ICP-AES in steels is described. The procedure is based on a discontinuous generation of methyl borate, in concentrated sulphuric acid and phosphoric acid medium, after injecting 45 microl of methanol in 20 microl of sample. The gaseous methyl borate and excess methanol are fed into the ICP torch via the intermediate tube by a flow of 430 ml/min Ar carrier gas, without disturbing the discharge. This work simplifies drastically the existing methodology of boron analysis in steels. Acid-soluble boron has been determined, but acid-insoluble boron can also be determined. The determination is carried out without iron interferences, with a reproducibility of 1.90% r.s.d. for a concentration of 20 microg/ml, and an absolute detection limit of 20 ng of total boron, working with a solution volume of 20 microl. | 18,965,797 |
Determination of mercury in zinc ore concentrate reference materials using flow injection and cold-vapor atomic absorption spectrometry. | A flow-injection, cold-vapor atomic absorption spectrophotometric method was developed for the determination of trace amounts of mercury in a proposed zinc ore concentrate Standard Reference Material (SRM 113b). The samples were digested with nitric and hydrochloric acids in closed Teflon digestion vessels. The experimental details for sample preparation and the flow injection method are discussed. The effect of matrix and various acid concentrations on the extraction and subsequent analysis of mercury were also studied. The method has a detection limit of 0.08 mug Hg/g in the sample. A certified reference material (CZN-1) was analyzed and the results obtained agreed well with the certified value. | 18,965,808 |
Solvent extraction separation of cobalt(II) from nickel and other metals with cyanex 272. | Cobalt(II) was quantitatively extracted at pH 8.0 with 5 x 10(-3)M Cyanex 272 [Bis(2,4,4 trimethyl pentyl) phosphoric acid] in chloroform. Cobalt(II) was stripped with 0.5M nitric acid and was determined by atomic absorption spectrometry as well as by spectrophotometry of the complex with nitroso R salt. Cobalt(II) was separated from vanadium, chromium, nickel, manganese, iron and zinc. Mixtures having different ratios of iron, cobalt and nickel were separated by proposed method. | 18,965,817 |
Polarographic determination of Ce(III) and Tm(III) using rare earth-DBF-chlorophosphonazo complex. | The electrochemical behaviour of the DBF-chlorophosphonazo (DBF-CPA)-rare earth (RE) complex has been investigated in this paper. A highly sensitive polarographic adsorption wave was found in the RE(III)-DBF-CPA system and a new method for determination of trace total RE(III) has been established. The limit of detection was 1.8 x 10(-8)M. The results of determination of the total RE(III) content in Chinese standard reference materials of cast-iron and alloy steel were in good agreement with the certified values. The polarographic adsorptive waves of Ce(III) and Tm(III)-DBF-CPA overlap seriously. In order to improve the selectivity of determination, a non-linear regression model was employed to fit the peak height of the polarographic wave and the concentrations of Ce(III) and Tm(III). The predictive accuracy of this model for simulant mixtures was satisfied. | 18,965,866 |
A time-based injector applied to the flow injection spectrophotometric determination of boron in plant materials and soils. | A simple and flexible time-based injector is described for the introduction of almost any desirable volume of sample and reagents in flow systems. The feasibility of application is demonstrated by improving the azomethine-H spectrophotometric method for the precise and accurate determination of boron in soil and coffee plant tissues. On-line programmed functions include: sequential injections and zone trapping, with a significant reduction of sample and reagent consumption. | 18,965,877 |
Reliability of protonation constants of SNAZOXS oligomers. | Concentration protonation constants of variously protonated of oligomers of sulphoazoxine SNAZOXS were determined by regression analysis of potentiometric titration curves. The group and common parameters were estimated using different computational strategies of three regression programs, MINIQUAD, MIQUV and PSEQUAD. ANOVA proved that six various computational strategies of three regression programs have no significant influence on reliability of protonation constants estimated in comparison with the reproducibility of the titration. Chemical model of protonation equilibria L(2)H(5-), L(2)H(4-)(2), L(2)H(3-)(3), and L(2)H(2-)(4) and reaction scheme of oligomers protonation for SNAZOXS was found. | 18,965,893 |
Flow injection colorimetric method for the assay of vitamin C in drug formulations using tris,1-10-phenanthroline-iron(III) complex as an oxidant in sulfuric acid media. | A simple, fast and accurate colorimetric flow injection (FI) method suitable for the assay of vitamin C in drug formulations was proposed. In the method, vitamin C was injected into a flowing stream of iron(III) and then mixed with 1,10-phenanthroline in 0.05M sulphuric acid media. The mixture was allowed to react in a 45-cm long coil and the resulting solution of tris, 1-10-phenanthroline-iron(II) complex was monitored at 510 nm. The method was adopted by fully investigating the kinetics of the reaction and proposing a suitable mechanism. A throughput of 100 samples per hour was achieved with a relative standard deviation of 0.88% for vitamin C concentration range of 100-400 ppm. | 18,965,896 |
Solvent effect on the determination of sulfamethazine by room-temperature photochemically induced fluorescence. | Room-temperature photochemically-induced fluorescence (RTPF) was applied to the determination of sulfamethazine (SMT) in methanol, ethanol and 2-propanol. Optimal ultraviolet irradiation times ranged between 2 and 6 min. Linear calibration graphs were obtained over a concentration range of more than one order of magnitude. The relative standard deviations were within the range 1.4-2.2%. Limits of detection were between 40 and 80 ng/ml. The method was evaluated for its applicability to the analysis of SMT in pharmaceutical formulations. | 18,965,913 |
Discontinuous-flow potentiometric determination of chloride in a large-volume wall-jet cell using an ion-selective electrode based on a silver chloride film chemically deposited on a silver iodide support. | A robust and sensitive chloride ion-selective electrode can be prepared by modifying the surface of an iodide-selective electrode using the chemical reaction with mercuric chloride in an oxidizing medium containing excess chloride. A thin film of silver chloride is thus formed ensuring a rapid and reproducible response to chloride. The analytical parameters of this electrode are similar to those of commercial silver chloride ion-selective electrodes, but its electrical impedance and signal noise are substantially lower and the response somewhat faster. Its sensitivity toward surfactants is somewhat suppressed. The electrode was used for discontinuous flow potentiometric (DFP) determinations in a large-volume wall-jet cell in which the electrode surface can be continuously reactivated by a cleaning solution contained in the cell. The method was applied to determination of chloride in ground waters from an industrial waste dumping site. The limit of determination is low 9 mug Cl(-)/l (2.6 x 10(-7)M), the precision good (the relative standard deviation varies from 0.6 to 3.0% for chloride contents from 2.90 to 0.15 mg/l, respectively) and the method correlates satisfactorily with the results of an indirect AAS determination of chloride. The sample throughput is high-90 measurements can be carried out per hour, corresponding to 30-40 determinations per hour. | 18,965,926 |
Spectrofluorimetric analysis of cefoxitin in pharmaceutical dosage. | A fluorescence method involving sample pre-treatment is investigated concerning the determination of cefoxitin. A fluorescent product is formed when samples containing cefoxitin are subjected to alkaline hydrolysis with 1.0M sodium hydroxide and heated for 60 min at 90 degrees . The fluorescence is measured in ethanol/water medium (50% v/v) at approximately pH 2.0 provided by adding of 0.1M hydrochloric acid. The fluorescence excitation and emission maxima were 317 and 400 nm, respectively. The quantitative range is between 0.020 and 1.40 mug/ml. A detection limit of 2 x 10(-3) mug/ml was found. The proposed method has been applied to the determination of cefoxitin in commercial injections, saline and glucosed physiological serum. | 18,965,964 |
Determination of V(V), Nb(V) and Ta(V) as their 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol chelates by reversed-phase HPLC. | This paper reports the separation and determination of V(V), Nb(V) and Ta(V) by RP-HPLC using 5-Br-PADAP as a precolumn derivatizing reagent. On C(18) column, the three metal chelates can be separated on a baseline in 9 min with the mobile phase of methanol-water (59:41, v/v) containing tartaric acid (0.2%) and acetate buffer (pH 3.5, 10 mM). The detection limits of V(V), Nb(V) and Ta(V) are 0.13 ppb, 0.22 ppb and 1.79 ppb, respectively when S/N is 3. This method is simple and rapid, and has been used in mineral analysis with satisfactory results. | 18,965,983 |
Rapid simultaneous analysis of 1-naphthol and 2-naphthol in water samples by derivative variable-offset synchronous fluorescence spectroscopy. | Derivative variable-offset synchronous fluorescence spectroscopy is developed to improve the spectral resolution and the selectivity of fluorescence measurements. 1-naphthol and 2-naphthol are employed to evaluate the proposed coupled technique and the various spectral comparisons are conducted. Second derivative variable-offset synchronous scanning permits the rapid simultaneous identification and quantitative determination of 1-naphthol and 2-naphthol in a mixture from a single spectrum. 6.7-2000 ng/ml 1-naphthol and 3.6-500 ng/ml 2-naphthol can be quantified with 1-naphthol and 2-naphthol ratios of 40: 1-1: 10. The determination of 1-naphthol and 2-naphthol in various spiked water samples gave a mean recovery of 100.7% with a relative standard deviation of 2.8% for 1-naphthol and mean recovery of 99.7% with a relative standard deviation (RSD of 2.6% for 2-naphthol, respectively. | 18,965,985 |
Sensing of trace copper ion by a solid phase extraction-spectrophotometry using a poly(vinyl chloride) membrane containing bathocuproine. | A new sensitive and selective spectrophotometric method for the determination of trace copper using a poly(vinyl chloride) membrane containing 4,7-diphenyl-2,9-dimethyl-1,10-phenanthroline (bathocuproine) and o-nitrophenyl-octylether as the solid phase extraction medium. Copper(I) in an aqueous sample solution is trapped on the membrane with an anion species, picrate ion, to form copper(I)-bathocuproine-picrate complexes, and the copper complexes,i.e. copper(I), were concentrated in the membrane. The absorbance of the orange membrane was measured at 480 nm using a spectrophotometer, and the concentration of the copper was then calculated using a calibration graph, which expressed the relationship between the copper(I) concentration and the membrane absorbance after coloring for 10 min. The detectable concentration of copper in a sample solution was in the range of 1.5 x 10(-7)-4.3 x 10(-5)M. The reproducibility of the absorbances of membranes was 0.193 +/- 9.44 x 10(-3) with a 4.9% relative standard deviation on five repeated measurements for the sample containing 1.2 x 10(-5)M of copper(II) under the same experimental conditions. | 18,966,003 |
Influence of phospholipidic microenvironment on the performance of a polypyrrole enzyme electrode. | Enzyme loaded phosphatidylcholine vesicles have been introduced as a new component in the design of sensing layers for the direct coating of an amperometric transducer. For this purpose, choline oxidase was chosen as a model enzyme, and the resulting vesicles were mixed with an amphiphilic pyrrole derivative [12-(pyrrol-1-yl)dodecyltriethylammonium tetrafluoroborate]. A minute amount of this mixture was deposited and dried on a platinum electrode, then electropolymerized. Compared to a similar preparation omitting phospholipid, the sensitivity of the enzyme electrode increased from 0.06 to 0.85 mA .1. mol(-1). The response, obtained in less than 20 sec, was linearly related to the choline concentration within a broader range, extending from 2.5. 10(-7) to 3. 10(-5)M. | 18,966,018 |
Fiber optic chemical sensor for nitrite based on an electropolymerized cobaltporphyrin film. | Fiber optic sensors for nitrite were prepared by first electrochemically depositing a film of cobalt(II) tetrakis(o-aminophenyl)porphyrin, [Co(o-NH(2))TPP], on the surface of indium(tin) oxide glass slides. Then, the slides with the immobilized porphyrin were positioned at the tip of an optical fiber bundle. The response of the sensors was based on a change in absorbance caused by the interaction between nitrite and the poly[Co(o-NH(2))TPP] film. The sensors had a detection limit of 6 x 10(-9)M nitrite. The selectivity of the sensors was determined under both separate solutions and fixed interference conditions. The sensor had a long lifetime and was reversible. | 18,966,023 |
l- and d-Lactate assay in real milk samples with immobilized enzyme reactors and graphite electrode. | A sensitive flow system for the determination of l- and d-lactate in milk samples is described. l- and d-Lactate dehydrogenase, LDH, were immobilized on aminopropyl-controlled pore glass beads. l- and d-Lactate are oxidized to pyruvate in the presence of NAD(+) and NADH is produced. The electrochemical determination of NADH allows the measurement of the substrate involved in the reaction. We used a graphite-based anode sensor without any mediator at +500 mV vs. Ag/AgCl. The analytes were measured, in standard solutions, in the concentration range from 1 x 10(-6) to 4 x 10(-4)M using 1 mM NAD(+) concentration and 0.1M Tris buffer pH 9. Experiments with real milk samples showed large values of currents probably due to electroactive substances usually contained in milk. To eliminate interfering compounds a microdialysis probe coupled with a pre-oxidizing cell was used. This method of pre-treatment removes the interfering substances, but leaves the analytes under study unaffected. The procedure allows the determination of l- and d-lactate in milk samples in the concentration range from 1 x 10(-5) to 5 x 10(-4)M. The assay was applied to monitor continuously the bacterial fermentation of Staphylococcus aureus in UHT milk as an example of possible contamination detection in the manufacturing process. | 18,966,029 |
Application of pressurized sample preparation methods for the analysis of steels and copper alloys. | Pressurized sample preparation devices (High Pressure Asher, Pressurized Microwave Digestion system, compared with a PTFE decomposition vessel) were used to dissolve certified metal alloy samples (steel, copper) for ICP analysis. Based on the results of the analysis it was established that both up-to-date devices can be advantageously applied to quickly and quantitatively dissolve metal alloy samples. To dissolve the samples, two different kinds of acid mixtures (A: nitric and hydrochloric acid; B: nitric and hydrochloric and sulphuric and phosphoric acid) were used. The sample preparation is simpler and less time-consuming than the earlier commonly used methods, sample loss and degree of contamination are also reduced. Steel samples containing tungsten, titanium and niobium (less than 0.5%) can only be analyzed using a mixture of the four acids. By dissolving steel samples in the nitric and hydrochloric acid mixture, the concentration of their most common elements (Cr, Ni, Mn, V, Cu) as well as their S and P content can be determined. Copper alloy samples can be dissolved quickly by the pressurized microwave decomposition device using hydrochloric acid and diluted (1:1) nitric acid. | 18,966,041 |
Determination of chemical species of selected trace elements in fly ash. | Complex analytical methods have been developed for determining the chemical composition of fly ashes. Samples were collected at coal-fired power plants and municipal waste incinerators. Morphological investigations and single particle analysis were performed by SEM/EDAX method. A survey of mineralogical phases was made by X-ray powder diffraction and infrared spectrometry. Solvent-leaching experiments were carried out for the information on the mobility of metal pollutants under real environmental conditions. Copper, Ni, Co, Cr, Pb and Cd have been studied, and of the toxic metals, Cd has been found in exchangeable forms in a great amount. Mobile species of toxic metals may have an impact on the quality of receiving waters or on organisms in soils. | 18,966,051 |
Determination of trace metals and speciation of chromium ions in atmospheric precipitation by ICP-AES and GFAAS. | Sampling and analytical techniques used for determining trace metal concentrations in atmospheric precipitation waters collected in Hungary are presented. The results of the analyses are briefly discussed and special attention is devoted to chromium speciation. For the preconcentration of the trace metals a chelating cellulose, iminodiacetic acid ethylcellulose (IDAEC) microcolumn was used in a flow-injected system. Cd, Co, Cu, Fe, Mn, Ni, Pb, Ti, V and Zn were determined by ICP-AES. In precipitation water the concentrations of the trace elements were in the 0.1-50 mug/l. range. The two forms of chromium, Cr(III) and Cr(VI) were separated using IDAEC and the anion exchanger diethylamine ethylcellulose, respectively. Cr was determined by GFAAS. In atmospheric precipitation the concentration of Cr(III) was in the range of 0.1-0.4 mug/l. while that of Cr(VI) in the range of 0.04-0.1 mug/l. | 18,966,053 |
Determination of the total dissolved sulphide in the pH range 3-11.4 with sulphide selective ISE and Ag/A92S electrodes. | An electrochemical method for the determination of the total sulphide concentration of sewage water samples has been studied using a potentiometric cell containing either a sulphide ion selective ISE-glass electrode pair or a Ag/Ag(2)S electrode-glass electrode system. The performance of the two sulphide ion sensors was investigated and compared in both acidic and basic pH ranges. It was proved that the cell potential can be made directly proportional to the logarithm of the total sulphide concentration when both the pH < lg K(2) - 1.5 condition (acidic range) and also when the lg K(2) + 1.5 < pH < lg K(1) - 1.5 condition prevails in the system (alkaline range); where K(1) and K(2) are the first and second protonation constants of the sulphide ion, respectively. A suitable calibration method for a wide range of sulphide concentration is also presented for both ranges of the pH scale. The overall performance of the measuring system was tested using model solutions and real waste water samples. | 18,966,059 |
Flow injection analysis with detection at mercury drop electrode in the presence of surfactants. | The surfactant presence in a sample may cause distortion of the flow injection peak obtained with amperometric detection at a mercury drop electrode. Distortion depends on detection parameters and flow system operating parameters and in some cases it may be eliminated by their careful optimization. Introduction of fumed silica into the carrier solution allows the dynamic removal of surfactant during the sample passage through the mixing coil. In the case of higher surfactant concentration in the sample, addition of fumed silica directly to the sample may be effective. Examples with amperometric detection as well as anodic stripping and adsorptive stripping voltammetric detection are described. | 18,966,073 |
Rapid spectrophotometric method (aqueous and extractive) for the determination of titanium in silicate rocks. | A sensitive and highly selective aqueous as well as extractive spectrophotometric method has been developed for the determination of titanium(IV) using 2,3-dihydroxynaphthalene (H(2)ND) as a chromogenic agent. The reagent (H(2)ND) forms a 1:3 (TiOH(3+):ligand) complex at pH 4-9. The molar absorptivity and Sandell's sensitivity are 3.2 x 10(4) l . mol(-1)mol . cm(-1) and 0.001 microg/cm(2), respectively at lambda(max) 375 nm. The method has been found highly selective for Ti(IV) determination in rock samples. Solvent extraction of Ti(IV) in ethylacetate greatly improves the detection limit of the method. The method has been successfully applied to diverse silicate rock samples and results obtained are favourably comparable with those obtained from the tiron method. The reagent (H(2)ND) used in the present investigation is a much better variant than tiron for titanium(IV) determination in silicate rock samples in terms of sensitivity, selectivity, operational simplicity and economy. | 18,966,077 |
The use of linear potentiometric titration curves in the determination of alkalinity and acid-base properties of diluted solutions of humic substances. | A critical study of the use of Gran and modified Gran functions for the determination of alkalinity and acid-base properties of diluted solutions containing humic substances is presented. These solutions were composed of 340 muM HCO3(-)(3) in 0, 10, 20.5 and 41 mg/1. of sodium humate in order to simulate natural waters with different levels of dissolved organic carbon. The results showed that the alkalinity may be determined in good agreement with the expected value using both methodologies. The modified Gran functions give information about acid-base speciation in addition to the alkalinity. The application of the modified Gran functions for determination of humic acid pK(a)s and stoichiometry was studied under conditions simulating waters rich in natural organic matter in terms of humic acid concentrations. | 18,966,083 |
Retention and separation of some organic water pollutants with unloaded and tri-n-octylamine loaded polyester-based polyurethane foams. | The analytical utility of unloaded and polyester-based polyurethane loaded foams with tri-n-octylamine (TOA) in the removal of some phenols from water were carried out. In static mode, the TOA-loaded foams showed a good affinity of extraction towards the tested compounds as compared to the untreated foams. The various parameters affecting the retention efficiency of the tested compounds from aqueous media by the foam were examined via batch technique. The TOA-loaded foams were employed in column modes for the extraction and recovery of the tested phenols. The retention efficiency and the recovery of the tested compounds from the loaded foam column were up to 98.5%. Sorption of the compounds by the foam were brought by solvent extraction mechanism. The molecular weight and the pK(a) of the compounds play an important role in the extraction process. The height equivalent to a theoretical plate (HETP) of the TOA-foam column was found in the range 1.8-2.05 +/- 0.1 mm at flow-rates up to 10 cm(3)/min. Separation of some of the tested phenols was also carried out by the TOA-foam columns. The membrane properties of the polyester foam sorbents give unique advantages over conventional granular sorbents in rapid, versatile and effective separations and preconcentrations of the tested compounds. | 18,966,093 |
Determination of submicrogram amounts of Mercury(II) with 5-(2'-carbomethoxyphenyl)azo-8-quinolinol in presence of anionic surfactant by derivative spectrophotometry. | A new sensitive, rapid and selective method is proposed for the determination of mercury in submicrogram level. Mercury(II) forms an insoluble complex with 5-(2'-carbomethoxyphenyl)azo-8-quinolinol in aqueous medium at pH 4-4.8 which can be made soluble by the action of anionic surfactant. The dissolution of the complex results in an orange red colour which is stable for at least 20 hr. The molar absorptivity and Sandell's sensitivity are at 512 nm 8.00 x 10(4) l. mol(-1) . cm(-1) and 0.0025 mug/cm(2), respectively. Derivative spectrophotometry is used to achieve selectivity. | 18,966,100 |
Determination of dissolved selenium(VI) in freshwater. | A procedure is proposed for the determination of selenate in freshwaters with a high content of dissolved organic material. After passage through an XAD-8 column, selenate is collected on a strong anion exchanger and subsequently eluted with hydrochloric acid. Following conversion into the tetravalent state, selenium is determined using atomic absorption spectrometry after hydride generation and preconcentration in a cold trap system. The two-column procedure effectively separates selenium(VI) from possible organic interferents and allows quantification at the low ng/l. level. Results from the investigation of waters from lakes and streams indicate that selenium(IV) and (VI) may constitute a very small part of total dissolved selenium. | 18,966,120 |
Chromatographic behaviour of trace metal ions on a strong base anion exchange resin functionalized by azo ligands. | A model which allows the evaluation of the elution volume V(E) and the central point V(C) of the breakthrough curve of a metal ion at trace level on a chromatographic column containing a chelating resin is presented. V(E) and V(C) mainly depend on the complexation properties of the active groups, and on the acidity and composition of the aqueous solution, according to the Gibbs-Donnan model for the resin. The model has been tested in the case of strong base anion exchange resins in chloride form functionalized with two different sulphonated azo ligands (T-azo-C, T-azo-R). The chromatographic behaviour of copper(II) and thorium(IV) is as expected from the formation of a complex with the azo dye in the resin, while that of zinc(II) and cadmium(II) is fully described by also taking into account the formation of anionic chloro complexes inside the resin. | 18,966,122 |
Kinetic fluorimetric determination of Cu(II) and Zn(II) by their incorporation reactions into a water-soluble porphyrin. | Kinetics of incorporation of Cu, Zn, Fe, Co, Ni and Mn divalent ions into coproporphyrin-I in imidazole buffer solution, pH 7.0, has been studied by monitoring the decrease in fluorescence intensity of the free base porphyrin. All reactions followed simple second-order rate law, the rate constants being decreased in the order Zn > Cu >> Co > Fe >> Mn, Ni. the kinetic fluorimetric method for the determination of Cu(II) and Zn(II) using their incorporation reactions into the porphyrin was developed. Initial rate and fixed-time methods were used to construct calibration graphs over the range 0-1.0 x 10(-5)M of both metals. The analytical characteristics of the method and effect of foreign ions were determined. In the presence of sodium thiosulphate as the masking reagent the determination of micromolar concentrations of Zn in the presence of a 10-fold excess of Cu is possible. | 18,966,123 |
A rapid and mercury pollution-free redoximetry determination of total iron in copper ore. | A rapid and mercury pollution-free method for the determination of total iron in the presence of copper is described. The sample was decomposed either by an acid attack of hydrochloric acid-nitric acid (1 + 2) or by fusion with sodium peroxide. The ferric ion in the sample solution was amenable to direct reduction to ferrous ion with potassium borohydride in sulphuric acid medium under the catalysis of cupric ion, followed by titration with potassium dichromate using sodium diphenylaminesulfonate as an indicator. After reduction, the iron (II) in the solution was stable for 300 min. The proposed method is free of interference from copper and has been successfully used for the large-scale routine determination of total iron in copper ores showing the same or better degree of precision and accuracy as those obtained by the classic standard stannous chloride-mercuric chloride method with the separation of iron from copper. | 18,966,137 |
Tris(2-ethylhexyl)phosphate as an extractant for trivalent gallium, indium and thallium. | A systematic study of solvent extraction behaviour of gallium(III), indium(III) and thallium(III) with tris(2-ethylhexyl)phosphate from salicylate media has been undertaken and a scheme for their separation is proposed. The optimum extraction conditions are evaluated and described. The method is applicable to the analysis of standard aluminium and aluminium alloys samples. The results obtained are reproducible and accurate. | 18,966,155 |
Fluorimetric determination of phenothiazine derivatives by photooxidation in a flow-injection system. | Flow-injection analysis (FIA) was combined with photochemically induced fluorescence (PF) detection for the determination of four phenothiazine derivatives, including unsubstituted phenothiazine, thionine, Azure A and Methylene Blue. The working analytical parameters (flow-rate, injected volume, photoreactor length) were optimized. Linear calibration graphs were obtained over about two orders of magnitude, with relative standard deviation within the range 1-2.3%. Limits of detection were between 13 and 35 ng/ml, according to the compound. The FIA-PF method was applied to the determination of phenothiazines in urine samples. Mean recoveries ranged from 94 to 117%. | 18,966,160 |
Sequential and rapid determination of Po-210, Bi-210 and Pb-210 in natural waters. | A sequential and rapid separation method for the determination of radon daughter nuclides, Pb-210, Bi-210 and Po-210 has been developed for application to natural waters. Rapid separation is attained by the use of the same hydrochloric acid solution. After isolation of the three radionuclides from the sample by co-precipitation with added Fe(3+), polonium isotopes are first spontaneously deposited onto a silver disc from a 0.5N hydrochloric acid solution. Next, bismuth isotopes are electrodeposited onto a platinum net cathode coupled with a platinum coil anode at 1.2 V. Finally, lead isotopes are electrodeposited onto a platinum net cathode at 1.8 V from the remaining solution by adding hydroxylamine hydrochloride as an anodic depolarizer. This method can be applied to meteorological precipitation samples where these three nuclides are separated within 10 hr after the sampling with chemical yields of more than 80% for Po-210 and Bi-210 and more than 70% for Pb-210. This method is applicable to other environmental water samples. | 18,966,174 |
Colorimetric method for determination of chlorine with 3,3',5,5'-tetramethylbenzidine. | A new method is developed for the calorimetric determination in water of chlorine (free and combined) with 3,3',5,5'-tetramethylbenzidine. The procedure proposed achieves a detection limit of 2 ng/ml and its sensitivity is greater than that of the methods used at present. | 18,966,176 |
A PC compatible computer program for the calculation of equilibrium constants by the simultaneous processing of different sets of experimental results. | A new PC compatible computer program SIRKO for the calculation of the equilibrium constants by means of the simultaneous processing of different experimental data from various techniques is given. This program is characterized by the application of a universal response function, which allows many different physicochemical methods to be used to study equilibria without any modification of the program. It is also possible to refine additional parameters (electrode parameters, initial analytic concentration, etc). We have used the least-squares method with the weightings calculated according to the error propagation rule taking into account all independent variables. To minimize the function, singular Jacobian decomposition is applied. This allows control of its range and forms a set of parameters, determined from the experimental data. | 18,966,178 |
Simultaneous determination of sulfite and phosphate in wine by means of immobilized enzyme reactions and amperometric detection in a flow-injection system. | A flow-injection system is proposed for the simultaneous determination of sulfite and phosphate in wine. A sulfite oxidase immobilized reactor and purine nucleoside phosphorylase-xanthine oxidase co-immobilized reactor are incorporated at fixed positions (parallel configuration) in the flow line, which is based on the splitting of the flow after sample injection and subsequent confluence. A poly(1,2-diaminobenzene)-coated platinum electrode is used as an amperometric detector to detect selectively hydrogen peroxide generated enzymatically in the enzyme reactors, without any interference from oxidizable species and proteins present in wine. Because each channel has a different residence time, two peaks are obtained. The first peak corresponds to sulfite and the second peak to phosphate. The peak current is linearly related to the concentrations of sulfite between 1 x 10(-5) and 2 x 10(-3)M and phosphate between 2 x 10(-5) and 5 x 10(-3)M. The simultaneous determination of sulfite and phosphate in wine can be performed at a rate of 30 samples/hr with satisfactory precision (less than 1.2% RSD) and no pretreatment except for the sample dilution. | 18,966,179 |
A new equation for wavelength dispersive x-ray fluorescence analysis without standards. | We derive an iteration equation for calculation of the concentrations of the elements in X-ray fluorescence analysis without standards. It does not require calculation of the intensity of primary spectra, which can excite the characteristic fluorescent X-ray, so its calculation is simpler. The experiments show that the results derived by the method without standards converged to those by chemical analysis, after three to four iterative calculations. The influence of the configuration of the specimen is negligible. | 18,966,180 |
Thin-layer chromatographic detection of monocrotophos in biological materials. | An organophosphorus insecticide monocrotophos is increasingly being used in agriculture to control insects on a wide range of crops. Its ready access has resulted in misuse in many instances of homicidal and suicidal poisoning cases. This paper describes a chromogenic spray reagent for the detection of monocrotophos in biological materials by thin-layer chromatography. Monocrotophos on alkaline hydrolysis yields N-methylacetoacetamide which in turn reacts with diazotized sulphanilamide or sulphanilic acid to give a red colour. Other organophosphorus insecticides do not give a coloured spot. Moreover, organochlorine and synthetic pyrethroid insecticides and constituents of viscera (amino acids, peptides, proteins etc.) which are generally co-extracted with the insecticides, do not interfere. However, phenolic compounds and hydrolysed product of carbamate insecticides, may interfere and are differentiated from monocrotophos by R(F) values. The limit of detection is ca 1 mug. | 18,966,181 |
Flow-injection fluorimetric analysis of sulfamethoxazole in pharmaceutical preparations and biological fluids. | A fluorimetric procedure for the determination of sulfamethoxazole using flow injection analysis is proposed. A two channel system is optimized for the fluorescent reaction with o-phthaldialdehyde and beta-mercaptoethanol. The detection limit is 0.007 mug/ml. No fluorescence is generated by the metabolite N-acetylated sulfamethoxazole. The method is applied to the determination of sulfamethoxazole in pharmaceuticals, urine and bovine serum samples without matrix interference problems. | 18,966,186 |
Potential characteristics of a pseudoliquid membrane electrode including coordinatively solvated UO(2)(NO(3))(2).2TBP complexes. | Mechanisms of formation of electrode potential with a pseudoliquid membrane phase including uranyl nitrate complexes coordinatively solvated by tri-n-butyl phosphate were investigated. It was stated that the electrode function of these membranes could be of cationic or anionic character depending on concentration UO(2) (NO(3))(2) in an aqueous phase. The influence of extraction and salting out on membrane phase composition and the slope of calibration curve was studied. It was shown that in the concentration range c > 0.1M the electrode potential depends on value of salt distribution coefficient between aqueous and organic phases. The dependence describing the electrode function in this concentration range was derived. | 18,966,190 |
Adsorptive stripping voltammetry of trace manganese in the presence of 2-(5'-bromo-2'-pyridylazo)-5-diethylaminophenol (5-Br-PADAP). | Trace levels of manganese can be determined by voltammetry after controlled adsorptive accumulation of the manganese-2-(5'-bromo-2'-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) complex on a hanging mercury drop electrode. Optimal conditions include an ammonia buffer solution (pH 8.8) containing 1 x 10(-5)M 5-Br-PADAP and an accumulation potential of -1.20 V. The technique offers enhanced sensitivity over analogous measurements of the manganese-Eriochrome Black T chelate. The detection limit is 0.2 mug/1 with 1 min accumulation. The new adsorptive approach is characterized with new selectivity dimensions (compared to the Eriochrome Black T scheme), and is not affected by large excess of commonly coexisting calcium and magnesium cations (which severely interfere in the Eriochrome Black T procedure). | 18,966,234 |
Optimal acidity of complexes by solution of polynomials and by iteration. | The methods for optimal acidity of complexes M(x)L(y)(OH)(m)H(n) based on direct iteration or solution of polynomials are described and discussed. Then, by a direct straightforward method of computation (that does not require any iteration) the complexes M(x)L(OH)(m)H(n) and ML(y)(OH)(m)H(n) are treated (where 1 x 3 and 1 y 3). Finally, the conditions leading to formation of polynuclear complexes are shown and discussed. The importance of study of polynuclear complexes for solving of biochemical problems is pointed out. Practical examples are given for each method. | 18,966,247 |
Colorimetric determination of low pH with Malachite Green. | A spectrophotometric method was developed for determination of concentration-based pH values from 0 to 2 with Malachite Green indicator. A quadratic model equation was based on the ratio of the absorbances of the peak at 618 nm and the isosbestic point at 518 nm. Normalization to the isosbestic point was used to stabilize the response because the color faded; the useful time interval was within 5 min after indicator addition. Model and verification sets agreed within +/-0.02 pH units between pH 0.3 and 1.8. This excellent precision makes the colorimetric method useful for acid determinations with a relative precision of > +/-5%. The presence of salts at a salt/acid equivalent ratio >0.1 caused a low pH bias. | 18,966,252 |
The trifluoroacetic anhydride-sodium iodide system as a reagent for determination and microdetermination of nitroxide radicals. | A trifluoroacetic anhydride-sodium iodide mixture (TFAA-I) reacts with nitroxide radicals with liberation of iodine. Since stoichiometric amounts of iodine are formed from nitroxides, the TFAA-I reagent can be applied to their analytical determination. Two procedures for the determination of nitroxides (titrimetric on mumol and spectrometric on nmol levels) are described. | 18,966,259 |
Determination of lead in preserved egg by flame atomic absorption spectrometry after chemically modified preconcentration. | A sensitive method for the determination of lead in preserved egg by flame absorption spectrometry using ammonium pyrrolidine dithiocarbamate-polystyrene chemically modified platinum wire matrix is presented. The modified platinum wire matrix, after preconcentrating the lead, is placed in a flame burner for direct atomization and measurement. The concentration range is linear between 5 and 500 ng/ml lead in solution and the detection limit is 0.65 ng/ml. This new technique is sensitive and convenient. | 18,966,264 |
A multi-wavelength photometer based on light-emitting diodes. | The light originating from seven light-emitting diodes of different colours is guided, one at a time, into a measuring cell by means of a fibre optic coupler. Detection is carried out with photodiodes which are connected to a log-ratio amplifier yielding direct absorbance readings. Optical filters are used to narrow the emission band from blue light emitting diodes as these bands are relatively wide compared to those of the emitters of other colours. An inexpensive and compact multi-wavelength photometer covering the visible range is thus obtained, which in many cases can replace a conventional spectrophotometer for absorbance measurements. The performance for a range of commonly used photometric analytical procedures is described and compared to conventional measurements with a spectrophotometer. | 18,966,270 |
Phase-inversion cellulose acetate membranes for suppression of protein interferences in anodic stripping voltammetry. | The phase-inversion (PI) method was used to cast permselective cellulose acetate membranes on glassy carbon electrodes with the aim of suppressing protein interferences in anodic stripping voltammetry (ASV). By using cadmium and lead as test analytes and differential pulse ASV as detection method, it was found that the modification of the electrode greatly reduces the interference from albumin. Cellulose acetate membranes prepared by the PI method give better protection against protein interference and have more reproducible permeability characteristics than membranes of comparable thickness prepared by the base hydrolysis method. An optimization study of the PI coating procedure was undertaken. | 18,966,290 |
Electrocatalytic oxidation and flow detection of cysteine at an aquocobalamin adsorbed glassy carbon electrode. | A chemically modified electrode (CME) constructed by adsorption of aquocobalamin (VB12a) onto a glassy carbon electrode surface was demonstrated to catalyze the electro-oxidation of cysteine, a sulfhydryl-containing compound. The sulfhydryl oxidation occurred at 0.54-0.88 V vs. Ag AgCl depending on pH value (3.0-10.0). The electrocatalytic behavior of cysteine is elucidated with respect to solution pH, operating potential and other variables as well as the CME preparation conditions. When used as the sensing electrode in flow injection amperometric detection, the CME permitted detection of the compound at 0.8 V. The detection limit was 1.7 pmol. The linear response range went up to 1.16 nmol. The stability of the CME was shown by RSD (4.2%) over 10 repeated injections. | 18,966,306 |
Separation mechanism exploration on metal-MBTAE-salicylic acid mixed ligand complexes by reversed-phase high performance liquid chromatography. | The separation and determination of platinum metal and co-existing metal complexes by reversed-phase high performance liquid chromatography (HPLC) with 2-(6-methyl-2-benzothiazolylazo)-5-diethylamino phenol (MBTAE) as a precolumn derivatizing reagent is presented. The separation mechanism of these complexes was investigated by combining spectrophotometry with HPLC while salicylic acid was contained in the mobile phase. The results show that most platinum metal ions, Co(II) and Cu(II) can form ternary mixed ligand complexes with MBTAE and salicylic acid. The relationship of the retention behavior of complexes and the surface tension of the mobile phase (gamma), the column temperature (T), and the composition and space configuration of complexes was also investigated. Some possible configurations of complexes are also proposed. These may all be illustrated well from the viewpoint of solvophobic theory. These method allowed the prediction of the composition and structure of metal complexes by utilizing HPLC. | 18,966,309 |
Tensammetric determination of non-ionic surfactants combined with BiAS separation procedure (Wickbold) 2. Optimisation of the precipitation and investigation of interferences. | The precipitation step in the developed procedure (BiAS-ITM) was optimised with the aim of achieving a lower detection limit. Losses during filtration using Triton X-100 as representative non-ionic surfactant (NS), the indirect tensammetric method (ITM) and adsorptive stripping tensammetry (AdST) for the determination of the concentration of the surfactant in the precipitate and in the filtrate were investigated. The G4 glass filter recommended up to now was found to be insufficiently effective and a source of loss. The new version of the procedure developed works within the range 2-1000 mug of NS in the sample, and thus two orders of magnitude lower than the former version of the procedure, showing satisfactory recovery and precision. The detection limit (3 x S.D.) was found to be below 1.5 mug in the sample. Interferences of anionic surfactants (ASs) e.g. sodium dodecylbenzenesulphonate and sodium lauryl sulphate, lipids, e.g. glycerol trioleate (GTO), and chlorophyll were investigated. GTO and AS show no effect on the BiAS-ITM results although strong adsorption of ASs on the glass filter as well as a slight adsorption on the precipitate was found. Chlorophyll does not interfere with the determination up to 30 mug in the sample, whereas higher concentrations produce results that are too high. | 18,966,351 |
A beta-cyclodextrin based fiber-optic chemical sensor: a fractal analysis. | A fractal analysis is presented for the binding of pyrene in solution to beta-cyclodextrin attached to a fiber-optic chemical sensor. The specific (k(l)) and non-specific binding rate coefficients and the fractal dimension (D(f)) (specific binding case only) both tend to increase as the pyrene concentration in solution increases from 12.4 to 124 ng ml(-1). Predictive relations for the binding rate coefficient (specific as well as non-specific binding) and for D(f) (specific binding case only) as a function of pyrene concentration are provided. These relations fit the calculated k(l) and D(f) values in the pyrene concentration range reasonably well. Fractal analysis data seem to indicate that an increase in the pyrene concentration in solution increases the "ruggedness" or inhomogeneity on the fiber-optic biosensor surface. The fractal analysis provides novel physical insights into the reactions occuring on the fiber-optic chemical surface and should assist in the design of fiber-optic chemical sensors. | 18,966,390 |
Fluorimetric determination of hydrogen peroxide in water using acetaminophen. | A fluorimetric procedure for the determination of hydrogen peroxide, based on the oxidation of acetaminophen with hydrogen peroxide in acidic medium, is described. The calibration graph was linear in the range 5.0 x 10(-8) - 2.4 x 10(-5) M hydrogen peroxide at an emission wavelength of 333 nm with excitation at 298 nm. The method has been applied to the determination of hydrogen peroxide in rain water, and the recoveries in milk samples were good. | 18,966,391 |
Dissolved oxygen removal from aqueous media by the chromatomembrane method. | The possibilities of the new chromatomembrane method in the removal of oxygen dissolved in water are studied. The scheme of the water deoxygenation process is determined. The new reagent-free method allows production of water with oxygen content at the level of a few ppb. | 18,966,405 |
Chemiluminometric flow-injection method for determination of free l-malate in wine with co-immobilized malate dehydrogenase/NADH oxidase. | A flow-injection system with a co-immobilized malate dehydrogenase/reduced nicotineamide adenine dinucleotide (NADH) oxidase reactor and a chemiluminometer is described for the determination of free l-malate in wine. Malate dehydrogenase and NADH oxidase were co-immobilized on poly(vinyl alcohol) beads and packed into a stainless-steel column (5 cm x 4 mm i.d.). The hydrogen peroxide produced was detected chemiluminometrically via a luminol-hexacyanoferrate(III) reaction. The calibration graph was linear from 3 x 10(-7) M to 2.5 x 10(-4) M (the linear correlation coefficient was 0.9998); the detection limit (signal-to-noise ratio, 3) was 8 x 10(-8) M. The sample throughput was 30 h(-1) without carryover. The ractor was renewed every 2 weeks. | 18,966,411 |
Salicylate-selective electrode based on lipophilic tin(IV)phthalocyanine. | A new PVC membrane electrode based on lipophilic (2,9,16,23-tetra-tert-butylphthalocyanine)tin(IV) dichloride which demonstrates excellent selectivity and fast response toward the salicylate ion is described. The membrane electrode displayed a linear response for salicylate in the concentration range 10(-5)-0.1 M and exhibited an antiHofmeister pattern, with high selectivity for salicylate compared with lipophilic inorganic and biologically important organic anions. The electrode was successfully applied to the determination of salicylate in pharmaceutical preparations and biological samples. | 18,966,414 |
Lead determination at the ppb level using stopped-flow FIA. | A flow-injection-based kinetic method for the determination of lead ions was developed. In this method, resazurin was reduced to resorufin by sulfide and lead ions. The method has a detection limit of 1 ppb with a relative standard deviation of 5.2% at the 20 ppb level. Interferences can be removed by prior extraction. | 18,966,424 |
Inorganic tin(II) determination by FIA with amperometric detection of its oxinate complex. | A highly selective, rapid and direct amperometric method, based on the formation of a complex between tin(II) and 8-hydroxyquinoline (oxine), has been developed for the determination of trace levels of tin(II) using flow injection analysis. Tin(II) electro-oxidation was catalyzed by oxine; its oxidation peak occurred at +0.05 V vs. Ag/AgCl at a glassy carbon electrode in 0.1 mol 1(-1) acetate buffer (pH 6). A linear relationship was obtained between the peak current and the tin(II) concentration in the range 0.25-20 mumol 1(-1). The detection limit was 0.1 mumol 1(-1) and the relative standard deviation calculated by the injection of a 10 mumol 1(-1) tin(II) solution was 5% (n = 20). Optimization of several experimental parameters has been carried out and the influence of numerous cations and possible interfering molecules encountered in radiopharmaceuticals and in dental gels has been investigated. The method was applied to the determination of tin(II) in dental gels. | 18,966,427 |
Spectrophotometric study of coproporphyrin-I complexes of copper(II) and cobalt(II). | The reagent 3,8,13,18-tetramethyl-21H,23H-porphine-2,7,12,17-tetrapropionic acid or coproporphyrin-I (CPI) was used for the spectrophotometric determination of copper(II) and cobalt(II) in the presence of pyridine and imidazole catalysts. Optimum conditions were investigated and the methods were applied to the determination of parts per billion levels of copper(II) and cobalt(II). The Sandell sensitivities of the recommended procedures were 0.568 mum cm(-2) and 0.464 mug cm(-2) (for A = 0.001) for copper and cobalt, respectively. The relative standard deviations were 2.0% for copper and 1.0% for cobalt. The kinetics of the reaction of CPI with copper(II) and cobalt(II) in the presence of the catalysts and the influence of the temperature were studied, and their kinetic constants determined. The influence of light on the photodecomposition of CPI was also studied. | 18,966,431 |
Electrochemical approach to monitoring metal exchange reaction of acetylacetonate complexes with cadmium, copper and zinc ions. | Metal exchange reactions of acetylacetonate complexes with Cd(II), Cu(II) and Zn(II) ions were investigated by using cadmium and copper ion selective electrodes. Changes in the electrode potential and pH of the solutions were monitored upon adding the pertinent metal Zn(II) of the acetylacetonate (AA) complexes. In the reverse system in which a stable Cu-AA complex exists in the solution prior to adding a secondary metal ion (Cd(II) or Zn(II)), no Cu(II) was replaced by either ion. In the systems containing Cd(II) and Zn(II) as a complexed form with AA or as free ions, the exchange reactions were not explained by considering the equilibrium stability constants of the Cd-AA and Zn-AA complexes. | 18,966,434 |
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