title stringlengths 0 1.13k | abstract stringlengths 1 15.7k | PMID int64 22 36.5M |
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Determination of antimony in lead-zinc concentrates and other smelter products by atomic absorption spectrometry after extraction with di-isopropyl ether and reductive stripping. | Several papers have appeared in the literature describing the determination of antimony, where antimony(V) is extracted into the organic phase and the organic solutions directly analyzed by atomic absorption spectrometry (AAS). This paper describes a procedure where antimony from the organic solution is reductively stripped into an aqueous phase and analyzed for antimony by AAS. The advantage of the method for a routine process control laboratory is highlighted. | 18,966,445 |
Simultaneous determination of penicillin and ampicillin by spectral fibre-optical enzyme optodes and multivariate data analysis based on transient signals obtained by flow injection analysis. | A multicomponent detection system using optical biosensors and flow injection analysis is described. The analysis of mixtures containing penicillin and ampicillin was realised by evaluating dynamic measurements of Phenol Red spectra in penicillinase optodes in combination with a diode array spectrometer. A variety of optodes has been produced by changing the composition of the receptor gel and the working pH. A set of characteristic quantities (describing dynamic and static features) could be obtained for each optode. These were used to compare the predictivity of classical multivariate calibration methods as well as of an artificial neural network. In addition, different algorithms were applied for the evaluation of the spectral data in order to select the most appropriate method for feature extraction. In consequence, the information obtained from the multivariate calibration models was used to set up an optimal sensor array consisting of four optodes with different types of penicillinase at different working pH. | 18,966,453 |
PA.FPNS: its synthesis and use in spectrophotometric determination of magnesium. | A new polymeric chromogenic reagent PA.FPNS has been synthesized by condensing polyallylamine (PA) with 3-(4-formylphenylazo)-4,5-dihydroxynaphthalene-2,7-disulfonic acid (FPNS) and its properties studied. In alkaline media, PA.FPNS reacts with magnesium to form a water-soluble blue complex, whose absorption maximum is at 604 nm. The molar absorptivity (varepsilon) of the complex is 5.2 x 10(4)l mol(-1) cm(-1), which is four times that of the FPNS-Mg complex, and Beer's law is obeyed over the range 0-0.35 mug ml(-1) magnesium. Compared to the corresponding low-molecular-weight FPNS and other chromogenic reagents, PA.FPNS offers considerably improved sensitivity and selectivity for magnesium, which may be attributed to incorporating FPNS into a water-soluble polymer and the effect of the polymeric chain on the reaction microenvironment. Also, a simple and sensitive spectrophotometric method for the determination of magnesium has been developed and applied to water and human fluid samples with satisfactory results. | 18,966,458 |
Study of complex formation in the manganese(II)/azide system. | The complex formation between Mn(II) cations and N(3)(-) anions was studied in aqueous medium at 25 degrees C and ionic strength 2.0 M (NaClO(4)). Data of average ligand number, n (Bjerrum's function), were obtained from pH measurements on the Mn(II)/N(3)(-)/HN(3) system followed by integration to obtain Leden's function, F(0)(L). Graphical treatment of data and a matrix solution of simultaneous equations have given the following overall formation constants of mononuclear stepwise complexes: beta(1)=4.15+/-0.02 M(-1), beta(2)=6.61+/-0.04 M(-2), beta(3)=3.33+/-0.02 M(-3), beta(4)=0.63+/-0.01 M(-4). A linear plot of log K(n) vs. (n-1) shows no change in the configuration during complex formation. Slow spontaneous oxidation of solutions to Mn(III) occurs when the N(3)(-) concentration is greater than 1.0 M. | 18,966,464 |
Chemiluminescence flow sensor for the determination of ascorbic acid with immobilized reagents. | A novel flow sensor based on chemiluminescence (CL) for the determination of ascorbic acid has been proposed. The analytical reagents, luminol and ferricyanide, were both immobilized on an anion-exchange resin column. The CL signal produced by the reaction between luminol and ferricyanide, which were eluted from the column through sodium phosphate injection, was decreased in the presence of ascorbic acid. The CL emission intensity was linear with ascorbic acid concentration in the range 0.01-0.8 mug ml(-1); the detection limit was 5.5 x 10(-3) mug ml(-1). The whole process, including sampling and washing, could be completed in 1 min with a relative standard deviation of less than 5%. The sensor could be reused more than 100 times and has been applied successfully to the analysis of ascorbic acid in pills and vegetables. | 18,966,471 |
Determination of trace nitrite ion in water by spectrophotometric method after preconcentration on an organic solvent-soluble membrane filter. | A simple and rapid preconcentration technique, based on collecting trace nitrite on a membrane filter and dissolving the membrane filter in an organic solvent, has been applied to its spectrophotometric determination in water. At pH 2.0, nitrous acid diazotizes with p-aminoacetophenone. which is then coupled with N-(1-naphthyl)ethylenediamine, at the same pH. The azo dye formed is collected on a 0.45 urn nitrocellulose filter at pH 4.7 as its ion associate with dodecyl sulfate. The ion associate and filter are dissolved in a small volume of 2-methoxyethanol (methylcellosolve), and acidized with 0.05 ml of 2 M hydrochloric acid and the absorbance of the resulting solution is measured at 555 nm against a reagent blank. Detection limits better than O.1 mug/dm(-3) as NO(2)(-) can be achieved. The ions normally present in water do not interfere when sodium metaphosphate is added as a masking agent. The proposed method has been applied to the analysis of water samples from several sources, the recoveries of the nitrite added to the samples are quantitative, and results found are satisfactory. | 18,966,476 |
Enzyme sensors for determination of fish freshness. | A simple and rapid procedure for the determination of fish freshness was developed and applied to the determination of the K(1) parameter (freshness indicator): K(1) = ([HXR] + [HX])/([IMP] + [HXR] + [HX]) x 100, where [IMP], [HXR] and [HX] are inosine monophosphate, inosine and hypoxanthine concentrations, respectively. A platinum electrode is used to detect hydrogen peroxide produced by the enzymatic reaction catalysed by xanthine oxidase immobilised on the electrode surface. The determination of inosine and inosine monophosphate was performed by the addition of nucleoside phosphorylase, 5'-nucleotidase or alkaline phosphatase to the buffer solution. Parameters such as type of buffer, amount of enzymes and sample treatment were optimised. With this procedure a linear response was obtained in the concentration range 1 x 10(-6)-2 x 10(-5)mol 1(-1) for hypoxanthine, inosine and inosine monophosphate. The detection limit was 5 x 10(-7) mol 1(-1). | 18,966,489 |
Polarographic determination of mitoxantrone in pharmaceutical preparations and biological media. | An A.c. tast polarographic method for the determination of mitoxantrone in pharmaceutical preparations and biological media is described. The optimum pH for the extraction of the drug from various samples into a 4:1 mixture of chloroform-isopropanol is indicated. The effect of other parameters such as temperature, composition of supporting electrolyte and polarographic variables (drop time, a.c. voltage amplitude, voltage sweep rate) on the sensitivity and reproducibility of the method is also verified, and a simple and precise recommended method is proposed for the determination of mitoxantrone. The method is found to be applicable to the analysis of the drug in extracted phases at concentrations 5 x 10(-7) - 2.5 x 10(-5) M with a precision of about 1.5% (relative standard deviation). The limit of detection is calculated as 3.5 x 10(-7) M for both aqueous pharmaceutical preparations and biological media. | 18,966,501 |
Determination of total fluorine in five coal reference materials by proton-induced gamma-ray emission spectrometry. | The direct non-destructive proton-induced gamma-ray emission (PIGE) technique with a germanium detector was applied to the determination of total fluorine concentration in five coal reference materials (BCR 40, NIST 1632b, NIST 1635, SARM 20 and USGS CLB-1). Duplicate analyses were made from five randomly selected bottles of each coal. Individual data are presented and some problems (calibration, proton stopping power, effects of sample heating by the proton beam, background estimation) which were encountered during this study are discussed. Sensitivity and reproducibility of the determinations, and homogeneity of the coal samples with respect to fluorine contents by analysis of variance were investigated. The present data are also compared with the few published values for these reference samples, including other PIGE data. The use of synthetic standards and spiked samples in the present study suggested that the PIGE method was more accurate than other techniques. | 18,966,506 |
Influence of ionic strength and OH(-) ion concentration on the Cu(II) complex formation with EDTA in alkaline solutions. | D.c. polarographic data show that the complex formation of copper ions with EDTA depends markedly on the ionic strength of the solution at pH 8-10. This is primarily associated with the dependence of the fourth deprotonization constant of EDTA on the solution ionic strength: when it increases from 0.4 to 3.4, the pK(a4) value decreases from 9.5 to 8.2. According to polarographic and spectrophotometric data the degree of Cu(II) complexation increases at pH>10 due to transformation of the complex CuY(2-) to the more stable CuY(OH)(3-) (Y(4-), a fully deprotonized anion of EDTA), but it decreases with increase in alkalinity in a highly alkaline solution (pH>13.5). The latter result could be explained by the decrease in the EDTA anion activity. The calculated values of the activity coefficient are lower than 0.05 at pH>14. | 18,966,509 |
Combination of classical dry ashing with stripping voltammetry in trace element analysis of biological materials: review of literature published after 1978. | Critical statements have appeared recently in the literature concerning the need for classical dry ashing in trace element analysis of biological materials. In contrast, respected institutions (AOAC, Nordic Committee on Food Analysis, etc.) as well as numerous other laboratories have developed, verified, and/or successfully used classical dry ashing in practical analyses of a number of materials of biological origin. Hence, it is desirable to find out under which conditions the latter decomposition technique yields good and accurate results. Since electroanalytical techniques are among the most demanding with regard to the completeness of the biological matrix removal, we decided to critically review the literature published after 1978 in which classical dry ashing is combined with some version of electroanalytical measurement. It emerged from this review that in particular the charring step requires careful performing. When performed well, classical dry ashing leads to complete removal of the organic matrix and to accurate analytical results for a number of determined elements. | 18,966,515 |
Acid-base equilibria in gamma-butyrolactone studied by use of pH-ISFETs. | pH-ISFETs were used in the study of acid-base equilibria in gamma-butyrolactone (GBL). After the spectrophotometric determination of the pK(a) value of 3,5-dichloropicric acid, the pK(a) values and homo-conjugation constants of various acids (including the conjugate acids of bases) were determined potentiometrically using a Ta(2)O(5)-type pH-ISFET. The values of pK(a) in GBL were in a linear relation with those in propylene carbonate (PC) and 1.0 units smaller on average. The difference in pK(a) between GBL and PC was mainly attributable to the difference in proton solvation. The autoprotolysis constant of GBL, roughly estimated by a rapid titration with a Si(3)N(4)-ISFET, was about 30 on the pK(SH) scale. A comparative study was made of the response speeds of the Ta(2)O(5)- and Si(3)N(4)-type pH-ISFETs and a conventional pH-glass electrode. The result was Si(3)N(4)-ISFET > Ta(2)O(5)-ISFET > glass electrode. Because GBL is not stable against acids and bases, the use of pH-ISFETs was much more convenient than the use of the conventional glass electrode. | 18,966,530 |
A thin liquid film thickness shear mode bulk acoustic wave sensor for determination of Proteus mirabilis. | A thickness shear mode bulk acoustic wave sensor coated with a thin liquid culture medium film was developed and applied to determine the concentration of Proteus mirabilis (P. mirabilis). Experiments demonstrated that there was a good linear relationship between the turning point time and the logarithm of the P. mirabilis concentration in the range 2.0 x 10(2)-2.0 x 10(6) cells ml(-1). The detection was fast and accurate because of the sharp turning point of the response due to the thin culture film on the sensor surface. Other problems concerning the experiments are discussed in detail. | 18,966,534 |
Monitoring CP-93,393 reaction mixtures by flow-injection analysis-mass spectrometry. | CP-93,393 is a drug candidate at Pfizer. Flow-injection analysis-mass spectrometry (FIA-MS) was used to monitor reaction completion for CP-93,393 reaction mixtures. FIA-MS provides essentially instantaneous results, is relatively simple to operate, and is a universal system that can be used to monitor any reaction as long as the product has a molecular weight that differs from the molecular weights of the reactants. The mass spectrometer for these studies employed atmospheric pressure chemical ionization. Samples were introduced into the mass spectrometer with a flowing stream of solvent. | 18,966,555 |
Electroinjection analysis. The introduction of a new variant of flow-injection analysis and comparison with electrophoretically-mediated microanalysis. | A new method of mixing sample and reagent due to the difference in their electrophoretic mobilities is introduced. Unlike electrophoretically-mediated microanalysis, sample and reagent are injected from the opposite ends of a capillary tube. This method is compared with electrophoretically-mediated microanalysis. Experiments are performed showing the possibilities of this new method. | 18,966,561 |
Coprecipitation with disulfide for the determination of traces of cobalt in water by electrothermal atomic absorption spectrometry. | Nanogram quantities of cobalt (II) in 200 ml of water were quantitatively collected at pH 4 on a precipitate of disulfide, which is an oxidation product of dithiol (toluene-3,4-dithiol). The precipitate was separated by filtration and dispersed homogeneously in 2 ml of 0.05 mol l(-1) nitric acid with the aid of ultrasonic irradiation. The suspension was directly analyzed for cobalt by electrothermal atomic absorption spectrometry without serious background absorption. This simple preconcentration technique allows the detection of as little as 3 ng l(-1) (50 pmol l(-1)) of cobalt in water samples. The validity of the method was evaluated by using river and seawater certified reference materials. | 18,966,590 |
Adaptation of microthermal probes for the determination of biochemical species. | A glucose sensitive enzymatic thermal sensor based on a pair of commercial microthermal probes was fabricated by cross-linking of the corresponding enzymes (glucose oxidase and catalase) with bovine serum albumin onto the chip surfaces. The characteristics of this sensor were optimised by testing it in different conditions. To find the maximal sensitivity, the calibration curves of this sensor were measured in different buffer solutions with and without the addition of H(2)O(2) to the analysed samples at various rates of sample flow stream. Different buffer solutions and hydrogen peroxide concentraions were used to realise the principles of a chemical and biochemical amplification of the biosensor response. It was shown that the level of the biosensor response and its dynamic range increase if hydrogen peroxide is added to the analysed samples and depend on the type of buffer solutions tested and the rate of the sample flow stream. | 18,966,595 |
Microwave-assisted sample preparation in analytical chemistry. | The speed and efficiency of instrumentation for chemical analysis has improved dramatically over the past twenty years. Until recently, however, methods of sample preparation had not changed to keep pace, so this had become the slowest step in analytical chemistry methodology. The widespread adoption of domestic microwave ovens during the past twenty-five years has eventually led to their usage in chemical laboratories. Microwave technology has now advanced to the point where it is revolutionizing chemical sample preparation and chemical synthesis. Since the first application of a microwave oven for sample preparation in 1975, many microwave-assisted dissolution methods have been developed - these are applicable to virtually any kind of sample type. This review attempts to summarize all the microwave-assisted dissolution and digestion methods reported up to and including 1994. In addition, some very recent developments in continuous-flow automated dissolution systems are discussed, as is the emergence of databases and software packages related to the application of microwave technology to sample dissolution. There are 344 references. | 18,966,599 |
Measurement/data-processing method to improve the ruggedness of membrane-based sensors: Application to amperometric oxygen sensor. | This paper describes alternative measurement and data-processing approaches that can reduce effects of experimental variables on results obtained with a membrane-based sensor for oxygen. In the new approaches, the membrane-based sensor is first equilibrated with the sample solution, after which a polarizing voltage is applied and current vs. time data are recorded as the response decays toward a steady-state condition. Current vs. time data are then processed by a fixed-time option and an integration option designed to determine the charge corresponding to the total amount of oxygen inside the membrane when a polarizing voltage is applied. The current measured at a fixed time and the total charge varied linearly with oxygen concentration between 0.05 and 0.26 mmol l(-1). Pooled relative standard deviations (N = 35) for the measurement/data-processing step were near 0.4% for the new pre-equilibrium options compared to a value of 0.3% for the steady-state option. Dependencies of the pre-equilibrium options on membrane thickness and stirring rate in the most sensitive regions were at least two orders of magnitude smaller than for the steady-state option. | 18,966,615 |
Electrocatalytic modified electrode for remote monitoring of hydrazines. | A remote electrochemical sensor for field monitoring of hydrazine compounds is described. The new submersible probe relies on the coupling of an effective electrocatalytic modified electrode to a 50 ft long shielded cable. The catalytic surface, based on an electorpolymerized film of 3.4-dihydroxybenzaldehyde, offers low-potential detection of hydrazine compounds. Such catalytic activity results in high sensitivity and selectivity, and hence offers convenient measurements of micromolar hydrazine concentrations in untreated groundwater, river water or lake water samples. Coexisting sample constituents do not contrubute to the response. Operational conditions have been optimized to meet the spacific requirements of remote operation. The concept seems suited for the remote monitoring of other contaminants via the judicious choice of the surface modifier. | 18,966,616 |
Phase inversion cellulose acetate membranes for suppression of protein interferences in anodic stripping voltammetry 2(1). Improvement of the membrane preparation procedure. | Phase inversion (PI) cellulose acetate membranes were cast on glassy carbon electrodes from a solution containing acetone as solvent and aqueous magnesium perchlorate as pore former. It is shown that a significant improvement of the reproducibility and permselective properties of the membrane is obtained by allowing complete evaporation of the solvent in a controlled humidity environment before the membrane is gelated. By using cadmium and lead as test analytes and differential pulse anodic stripping voltammetry as the detection method, it was found that the modification of the electrode greatly reduces the interference from albumin, lysozyme, gelatin and polyethylene glycol (MW 6000). The permselectivity of the PI membrane can be controlled by varying the amount of magnesium perchlorate in the casting solution and the relative humidity during the pre-gelation conditioning of the membrane. | 18,966,617 |
Effect of alkyl substitueras in hydrophobic 8-quinolinol on the extraction of gallium(III) and applications to the separation of gallium(III) from aluminum(III). | The extraction of gallium(III) with newly prepared 5-alkyloxymethyl-8-quinolinol derivatives with alkyl substituent at the 2-position in 8-quinolinol moiety has been studied. The Ga(III)-5-octyloxymethyl-8-quinolinol (HO(8)Q), Ga(III)-2-methyl-5-octyloxymethyl-8-quinolinol (HMO(8)Q), Ga(III)-2-methyl-5-hexyloxymethyl-8-quinolinol (HM-O(6)Q), and Ga(HI)-2-n-butyl-5-hexyloxymethyl-8-quinolinol (HNBO(6)Q) complexes extracted in heptane from a perchloric acid medium were Ga(O(8)Q)(3), Ga(OH)(H(2)O)(MO(8)Q)(2), Ga(OH)(H(2)O)(MO(6)Q)(2) and Ga(OH)H(2)O)(NBO(6)Q)(2), respectively. The 2-tert-butyl-5-hexyloxymethyl-8-quinolinol did not exhibit any reactivity toward gallium(III). The extraction constants for Ga(O(8)Q)(3) (K(ex) = [Ga(O(8)Q)(3)](org) [H(+)](3)/[Ga(3+)][HO(8)Q](org)(3)), Ga(OH)(H(2)O)(MO(8)Q)(2) (K(ex) = [Ga(OH) (H(2)O)(MO(8)Q)(2)](org) [H(+)](3)/[Ga(3+)][HMO(8)Q](org)(2)), Ga(OH)(H(2)O)(2)(MO(6)Q)(2) and Ga(OH)(H(2)O)(NBO(6)Q)(2), which were extracted in heptane from an acidic solution, are 10(3.21 +/- 0.12), 10(-4.24 +/- 0.16), 10(-3.84 +/- 0.16) and 10(-4.07 +/- 0.07), respectively at I = 0.1 M and 25 degrees C. HNBO(6)Q exhibited very high selectivity toward gallium(III) in the presence of aluminum(III). Even in the presence of a 100 fold excess of aluminum(III) to gallium(III) (1.43 x 10(-5) M), gallium(III) was completely extracted and the distribution ratio of aluminum(III) was found to be less than 2.0 x 10(-3). | 18,966,627 |
Medium effect on acidity constants of some heterocyclic nitrogen azomethines. | The effects of different organic solvent-water mixtures on the acidity constants of some azomethines derived from 3-amino-1,2,4-triazol; 2-amino-1,3-pyrimidine and also 2-amino-4-methyl-1,3-pyrimidine have been examined. Two pK(a) values for the o-OH derivatives were determined; one is assigned to the deprotonation of the nitrogen azomethine group and the other one is ascribed to the ionization of the OH group. The p-OH derivatives give one K(a) due to the ionization of the OH group. On the other hand, it was observed that with the increase in the amount of organic solvent in the medium, the pK(a) of the compound studied is decreased. This behaviour can be accounted for in terms of the high stabilization of both the non-protonated and ionic forms of these compounds by dispersion forces rather than by hydrogen bonding. Also, the effects of medium polarizability on the K(a) values and thus on the spectra of the charge transfer band observed have been discussed. | 18,966,630 |
A series expansion of the extended Debye-Hückel equation and application to linear prediction of stability constants. | The Debye-Hückel semiempirical extended equation is frequently used to calculate activity coefficients of chemical species and equilibrium constants at ionic strengths different from those used in their experimental evaluation. A series expansion of the extended Debye-Hückel equation is proposed here and checked with experimental data taken from the literature. The expansion is linear in the ionic parameters and yields a geometrical series which converges rapidly and that enables the accurate calculation of interpolated and extrapolated activity coefficients and equilibrium constants by simple and multiple linear regression without previous knowledge of the ionic parameters. | 18,966,639 |
Spectrophotometric determination of bio-active compounds with chloramine-T and gallocyanine. | A simple, sensitive and selective method for the spectrophotometric determination of drugs, viz., sulphamethoxazole, tetracycline HCl, amidopyrine, nifurtimox and isoniazid and biologically important amino acids, cysteine, aspartic acid and arginine based on their reactivity with chloramine-T (CAT) is proposed. The method involves the addition of excess CAT of a known concentration in the presence of 0.25 M HCl and the determination of the unreacted CAT by measurement of the decrease in the absorbance of the dye, gallocyanine (lambda(max): 540 nm), the most suitable of several dyes that were tested. This method was applied to the determination of drug contents in pharmaceutical formulations and to the measurement of the aspartic acid content of some protein hydrolysates. The method is useful for the determination of the target compounds in microgram quantities from 0.4-5.6 microg mL(-1) with the exceptions of arginine (1.0-8.0 microg mL(-1)) and nifurtimox (0.8-5.6 microg mL(-1)). Standard deviations were typically 0.5 mg per dose (RSD 0.5-1.2%). No interferences were observed from common excipients in formulations, and detailed interference studies of other amino acids in the determination of cysteine, aspartic acid and arginine are reported. The validity of the method was tested against spectrophotometric and titrimetric reference methods. Recoveries were 99.8-102.1%. | 18,966,644 |
Chemiluminometric method for the determination of glycerol in wine by flow-injection analysis with co-immobilized glycerol dehydrogenase/NADH oxidase. | A flow-injection method for the determination of glycerol in wine is described. Glycerol dehydrogenase and NADH oxidase were co-immobilized on poly (vinyl alcohol) beads and incorporated in a flow-injection system. The hydrogen peroxide produced was detected chemiluminometrically via a luminol-hexacyanoferrate (III) reaction. Wine was diluted 1000-fold with water and sample solution (50 microl) was injected into the carrier stream. The calibration graph was linear in the range 3 x 10(-7)-3 x 10(-4) M; the detection limit was 7 x 10(-8) M and the sample throughout was 30 h(-1) without carryover. | 18,966,663 |
Fiber optic sensor for laser-induced room-temperature phosphorescence detection of polycyclic aromatic compounds. | The development of a fiber optic sensor for the analysis of polycyclic aromatic compounds based on laser-induced room-termperature phosphorimetry is reported for the first time. A pulsed nitrogen laser was used to excite phosphorescence emission from compounds imbibed on filter-paper substrates. Thallium(I) acetate (0.1 M) was used to enhance phosphorescence emission from chrysene, 1,2-benzofluorene, 7,8-benzoquinoline, phenanthridine and 5,6-benzoquinoline. Lead(II) acetate (0.5 M) was employed for the determination of fluoranthene, which showed no phosphorescence signal on paper substrates pre-treated with thallium(I) acetate. Limits of detection at the ng/ml(-1) level were estimated for all the compounds. An improvement in the limits of detection of the nitrogen heterocyclic compounds was obtained by using a low-background paper substrate. Satisfactory reproducibility of measurements was observed, varying from 6.1% (chrysene) to 11.9% (7,8-benzoquinoline). The linear behavior of the sensor response was also evaluated. Linear dynamic ranges extend over two and three orders of magnitude and show the potential of the device for the quantitative analysis of environmental pollutants. | 18,966,667 |
Ultraviolet spectrophotometric determination of copper in copper ores by flow-injection analysis. | A flow-injection analysis (FIA) method for the ultraviolet spectrophotometric determination of copper in copper ores is described. The ore samples are dissolved in concentrated perchloric acid, the excess acid is neutralized with ammonia solution, and the resulting solution is used for the determination of copper. The UV-FIA system is based on the reaction of copper (II) ions with pyrophosphate and subsequent measurement of the absorbance of the dipyrophosphatocuprate (II) complex at 240 nm. The main factors which control the formation of this complex and the FIA variables influencing the system are discussed. The calibration graph is linear from 2-50 ppm copper. At a sampling rate of about 70 samples h(-1) with 50 mul sample injections, precision was about 1% relative standard deviation. Results obtained compare well with those obtained by atomic absorption spectrometry. | 18,966,680 |
Utility of quercetin for determination of some tertiary amine and quaternary ammonium salts. | A simple and sensitive spectrophotometric method for the assay of eight drugs containing quaternary ammonium or tertiary amine moieties is described. The method is based on the interaction of these drugs with quercetin after its oxidation with N-bromosuccinimide (as counter ion) to give highly colored ion-pairing complexes extractable with organic solvents. The absorbances of the colored complexes are measured in the range of 528-560 nm. Beer's law is obeyed for the studied drugs in the range 5-30 mug ml(-1). The method is successfully applied to the analysis of the studied drugs in commercial dosage forms. | 18,966,683 |
Automatic determination of cobalt at the submicrogram per millilitre level using a flowthrough spectrophotometric sensor. | A flowthrough spectrophotometric sensor for the determination of cobalt at the nanogram per millilitre level using pyridoxal 4-phenylthiosemicarbazone as reagent and integrated preconcentration and detection in the flow cell is proposed. The method is highly selective for cobalt(II); it features detection and determination limits of 0.02 and 0.06 mug ml(-1) respectively, and a linear range of at least 0.04-18 mug ml(-1). The method is subject to very few interferences because the strongly acidic medium used prevents the formation of most complexes of the reagent with other metal ions. The method was applied to the determination of cobalt in pharmaceutical preparations. | 18,966,684 |
Extraction and determination of crown ethers from water samples using a membrane disk and gas chromatography. | A method for rapid extraction and determination of some crown ethers in aqueous matrices using octadecyl-bonded silica membrane disks and gas chromatography is presented. Extraction efficiency and the influence of vacuum pressure. pH, and type and least amount of eluting solvent used to extract the crown ethers from the membrane disks were evaluated. Extraction efficiencies > 95% were obtained for benzo-15-crown-5, benzo-18-crown-6 and dicyclohexyl-18-crown-6 using 5 ml of acetonitrile as eluting solvent. The limit of detection of the proposed method for the determination of the crown ethers is reported. | 18,966,705 |
Determination of nanogram levels of zirconium by chelating ion exchange and on-line preconcentration in flow injection UV-visible spectrophotometry. | Trace quantities of zirconium were preconcentrated on a series of chelating resins. The experimental conditions for preconcentration such as pH, time and metal ion concentration were optimized for the batch processes. Continuous flow manifolds were developed for the on-line preconcentration of zirconium using microcolumns containing chelating resins. Calibration plots were obtained with correlation coefficients of 0.9990 +/- 0.0008. The determination of zirconium was performed using Xylenol Orange at 535 nm. Binary and ternary mixtures of zirconium, thorium and titanium did not show any cross-contamination during column chromatographic separation. | 18,966,749 |
Solvent extraction separation of iron(III) and aluminium(III) from other elements with Cyanex 302. | A rapid method was developed for the solvent extraction separation of iron(III) and aluminium(III) from other elements with Cyanex 302 in chloroform as the diluent. Iron(III) was quantitatively extracted at pH 2.0-2.5 with 5 x 10(-3) M Cyanex 302 in chloroform whereas the extraction of aluminium(III) was quantitative in the pH range 3.0-4.0 with 10 x 10(-3) M Cyanex 302 in chloroform. Iron(III) was stripped from the organic phase with 1.0 M and aluminium(III) with 2.0 M hydrochloric acid. Both metals were separated from multicomponent mixtures. The method was applied to the separation of iron and aluminium from real samples. | 18,966,775 |
Solubility of metal chelates and their extraction from an aqueous environment via supercritical CO(2). | Solubility of nickel(II), copper(II), and chromium(III) hexafluoroacetylacetone and chromium(III) acetylacetone chelates was measured in supercritical CO(2) at two different pressures (200 and 400 atm) and 60 degrees C. Solubility of fluorinated acetylacetone chelates was at least an order of magnitude higher than the non-fluorinated complexes. These pre-formed metal chelates as well metal diethyldithiocarbamate (DDC) and metal bis(trifluoroethyl)dithiocarbamate (FDDC) have also been extracted from aqueous environment using pure supercritical CO(2). It was demonstrated that metal HFA chelates while exhibiting higher solubility in supercritical CO(2) compared with metal FDDC chelates, exhibited lower extraction efficiency using the same extraction conditions. This behavior of metal HFA chelates is related to their stability in an aqueous environment. Direct extraction of Ni(+2) and Cu(+2) from an aqueous matrix was also achieved via in-situ chelation using diethyldithiocarbamate and bis(trifluoroethyl)dithiocarbamate as the ligands. Bis(trifluoroethyl)dithiocarbamate proved to be a more effective ligand for direct extraction of metal ions from aqueous environment using supercritical CO(2). | 18,966,798 |
Flotation-spectrophotometric determination of trace of germanium with isochromatic dye ion-pairs formed by rhodamine 6G and tetrabromofluorescein. | A flotation spectrophotometric method for the determination of germanium with isochromatic dye ion-pairs is described. The molar ratio of germanium to rhodamine 6G to tetrabromofluorescein is 1:5:5. The apparent molar absorptivity is 5.8 x 10(5) l mol(-1) cm(-1) at 531 nm. Beer's law is obeyed over the concentration range of 5.0 x 10(-8)-1.25 x 10(-6) mol l(-1). The proposed method is sensitive and accuracy and can be applied satisfactorily to the determination of germanium in vegetables. | 18,966,829 |
Determination of trace amounts of some metals in samples with high salt content by atomic absorption spectrometry after cobalt-diethyldithiocarbamate coprecipitation. | A method for determination of trace amounts of Cu, Fe, Pb, Mn, Zn, Cd, Ni, Bi and Cr in aqueous solutions by flame atomic absorption spectrometry after coprecipitation by using a combination of sodium diethyldithiocarbamate as a chelating agent and cobalt as a carrier element was introduced. Different factors including amounts of reagents, pH of sample solution, standing time, sample volume for the precipitation and matrix effects were examined. Under selected conditions, the relative standard deviation of the combined method of sample treatment, coprecipitation and determination with flame AAS (n = 9) is generally about 3.5-6.9%; the limits of detection (3 s, n = 20) for the analytes were found to be between 4 and 64 microg 1(-1). The procedure was applied to the analysis of sea water and dialysis concentrate samples with quantitative recovery, > or =95%. | 18,966,833 |
Investigation of conductometric humidity sensors. | Sensors for determining humidity in air have been described and investigated. Sensing film of the devices was prepared from polyvinylalcohol and graphitized carbon black disperse phase. The composition, thermal treatment and design of sensing films were investigated and optimized. An optimized humidity sensor has better metrological parameters as compared with its prototype (response time approximately 45 s, detection limit 0.17%, slope 6.25 +/- 0.05 Theta/R.H., standard deviation of measurement 0.15%, standard deviation of analytical signal in the graduation equation 8.29Theta). Such construction of sensors have prospects in analytical practice. | 18,966,843 |
Fibre-optic pesticide biosensor based on covalently immobilized acetylcholinesterase and thymol blue. | A fibre-optic based on immobilized acetylcholinesterase is described and its application in the detection of carbamate and organophosphate pesticides through enzyme inhibition measurements is discussed. The bioactive component of the sensor consists of acetylcholinesterase covalently immobilized on preactivated isothiocyanate glass mixed with thymol blue indicator bound on aminopropyl glass and the sensor was constructed by packing a thin layer of the glass bead mixture at the tip of a bifurcated fibre-optic sensor head, which was then integrated with a flow-through cell. The response of the sensor to acetylcholine was highly reproducible (RSD<2%) and readily reversible. The sensor exhibited a linear response to acetylcholine in the concentration range 2.5-25 mM (r(2)=0.992). Inhibition plots obtained for test organophosphate (paraoxon) and carbamate (carbofuran) pesticides exhibited concentration-dependent behaviour and showed linear profiles in the concentration ranges 5x10(-8)-5x10(-7) M for carbofuran and 5x10(-7)-5x10(-6) M for paraoxon. The detection limits, calculated at I(10%), are 1.5x10(-8) M (3.1 ppb) and 1.1x10(-7) M (24.7 ppb) for carbofuran and paraoxon, respectively. The regeneration of paraoxon-inhibited sensor was possible using 2-pyrimidine aldoxime, while repetitive substrate injection was necessary to reactivate the carbofuran-inhibited optrode. The factors affecting the inhibition and reactivation processes were investigated. | 18,966,870 |
Spectrophotometric determination of hydrogen peroxide by using the cleavage of Eriochrome black T in the presence of peroxidase. | A new hydrogen donor for peroxidase, Eriochrome black T, was reported for the first time. Steady-state catalytic velocity depends upon enzyme and substrate concentrations, and a Michaelis-Menten K(m) value of 1.72x10(-5) mol l(-1) and a V(max) value of 4.43x10(-3) s(-1) were measured at pH 8.6. Trace amount of hydrogen peroxide (2x10(-7)-1.0x10(-5) mol l(-1)) was determined in aqueous solution by using the cleavage of Eriochrome black T catalyzed by peroxidase. The method is simple and practical, with high sensitivity and enzymatic activity. | 18,966,877 |
Preparation and analytical properties of a chelating resin functionalized with 1-hydrazinophthalazine ligand. | A poly[styrene-co-(divinylbenzene)] resin (XAD-4) functionalized with 1-hydrazinophthalazine ligand has been prepared and its analytical properties investigated. The pH dependence of sorption of metal ion on the resin has been determined for Cu(II), Ni(II), Co(II), Zn(II), Cd(II), Pb(II), Fe(III) and Cr(III). Trace amounts of these metal ions were quantitatively retained on the resin and recovered by eluting with 1 mol l(-1) hydrochloric acid. The resin was found to be selective for Fe(III) and its separation from other metal ions was carried out effectively. Metal ions concentrations were determined using AAS. | 18,966,882 |
Amperometric monitoring of lactate accumulation in rabbit ischemic myocardium. | Fabrication and characterization of miniature, flexible, planar biosensors for monitoring l-lactate accumulation in an ischemic myocardium are described. Three configurations of Au-based electrodes were fabricated by a photolithographic technique on flexible polyimide Kapton((R)) foil. All sensors are based on an immobilized lactate oxidase with amperometric detection of the enzymatically produced hydrogen peroxide at a platinum-electroplated-gold base electrode polarized at 0.5 V versus Ag/AgCl. An inner electropolymeric layer is used to prevent electrode fouling and to reject the interference effects of easily oxidizable molecules. In addition, a diffusion controlling outer layer that greatly enhances the linear dynamic range of the sensor, is obtained by casting a polyurethane external film. The developed sensor was evaluated in vitro and proved to have high selectivity, good operational stability, good accuracy and precision (average recovery = 102.3 +/- 0.4% for control sera), fast response time (t(95) = 20 s) and high upper limit of the linear dynamic range (25-80 mM, with sensitivity of 1.7-0.4 nA mM(-1) respectively at PO(2) = 15 mmHg). Subsequently, the sensor was brought into direct contact with the surface of the rabbit papillary muscle and used for continuous quantitative monitoring of extracellular lactate accumulation during no-flow ischemia. | 18,966,893 |
Calibration procedure for solid phase microextraction-gas chromatographic analysis of organic vapours in air. | A calibration procedure for solid phase microextraction-gas chromatographic (SPME-GC) analysis of organic vapours in air was described in which GC detector (MS in this case) signal is directly related to concentration of analytes of interest sampled by SPME. Gaseous standard mixtures used for the calibration were generated by means of a home-made permeation-type apparatus described elsewhere, W. Janicki et al., Chem. Anal., 38 (1993) 423 and modified to permit easy sampling of analytes on an SPME fibre. To establish sampling parameters, times for equilibrium partitioning of five selected organic compounds (carbon tetrachloride, toluene, chlorobenzene, p-xylene, n-decane) between gaseous mixtures and the fibre (fused silica fibre coated with 100 mum polydimethylsiloxane) were determined. For 10 min sampling time, the detector response and hence amount sampled on the fibre were linear functions of analytes concentration in a gaseous sample. | 18,966,894 |
Utilization of standards generated in the process of thermal decomposition chemically modified silica gel for a single point calibration of a GC/FID system. | The utilization of a multicomponent gaseous standard mixture, containing CO and CO(2) and obtained by thermal decomposition of a so-called immobilized compound, for a single point calibration of a GC/FID system are described. The generation of such a mixture takes place as a result of thermal decomposition of a sample of chemically modified silica gel placed in a heated chamber of thermal desorber coupled with the device being calibrated via a catalytic methanizer. The mean amount of the analyte librated from unit mass of the gel was 0.71 mg g(-1) (RSD = 3%) for carbon monoxide and 0.86 mg g(-1) (RSD = 3%) for carbon dioxide. | 18,966,895 |
Chemometric alternatives for resolution of classical analytical problems Spectrophotometric determination of lanthanide mixtures. | The simultaneous determination of lanthanide family elements is one of the greatest problems in analytical chemistry, due to the close similarity of their chemical properties. Spectrophotometric methods are generally of limited use, due to the various mutual spectral interferences involved. By using multivariate calibration methods (partial least-squares regression, PLSR), it was possible to obtain a model that adjusts itself perfectly to the values of the mixture concentrations used in the calibration. The model used absorption spectra in the 290-800 nm range for a set of 20 different mixtures of Ce, Pr, Nd and Sm, and made possible the determination of Ce, Pr and Nd concentrations of a commercial rare-earth product, with significantly greater precision than the conventional univariate calibration method. Determination of the Sm concentrations was not possible, since its concentration was below the concentrations used in the model definition. | 18,966,922 |
Extraction of uranium from aqueous solution by phosphonic acid-imbedded polyurethane foam. | Phenylphosphonic acid was imbedded into the matrix of the polyurethane foam during the fabrication process of the polymer. The extraction of uranium by phosphonic acid-imbedded polyurethane foam and blank polyurethane (i.e., foam without phosphonic acid functional groups) was investigated. Phosphonic acid-imbedded foam showed superior extractability of uranium from solutions with pH=7.0+/-1.5 over a wide range of temperature. | 18,966,928 |
Gas chromatographic determination of pollutants in the chlorination and caustic extraction stage effluent from the bleaching of a bamboo pulp. | The gas chromatographic detection and quantitative determination of various chlorophenolics as well as resin and fatty acids have been carried out in the chlorination and caustic extraction stage effluents generated in the laboratory by bleaching a bamboo pulp. A number of chlorinated phenols, catechols, guaiacols, syringaldehydes and resin acids as well as non-chlorinated saturated and unsaturated fatty acids together with resin acids have been detected. The concentration of various compounds detected have also been compared with the reported (96)LC(50) values. | 18,966,933 |
Potentiometric determination of stability constants of Lanthanon(III) complexes with some Schiff bases and benzothiazolines. | The protonation constants of five Schiff base and two benzothiazoline type ligands and stability constants of their complexes with six lanthanide ions were determined by potentiometrically in ethanol-water solution (1:1, v/v) at 25 +/- 0.1 degrees C. The Schiff base-type ligands were salicylidene 2-iminopyridine (SAPy), salicylidene-5-methyl-2-iminopyridine (SAPyMe), salicylidene-5-chloro-2-iminopyridine (SAPyCl), 2-(2-pyridylmethyleneamino) phenol (PyOH), 2-(2-quinolylmethyleneamino) phenol (QuOH) and the benzothiazoline-type ligands were pyridine-2-car-bozaldehydebenzothiazoline (PyS) and quinoline-2-carboxaldehydebenzothiazoline (QuS). The order of stability constants was found to be for metal ions La(III) < Pr(III) < Nd(III) < Eu(III) < Ho(III) < Yb(III), and for ligands SAPyCl < SAPy < QuS < QuOH < PyS < PyOH < SAPyMe. The FORTRAN programs PKAS and BEST were used for the calculation of protonation constants and stability constants, respectively. | 18,966,937 |
Multicomponent analysis in luminescence spectroscopy. | Multicomponent analysis of absorption spectra (infrared or electronic spectra) by factor analysis is a suitable method to use. The algorithm of factor analysis is now available for luminescence spectroscopy. The first possibility, as in absorption spectroscopy, is to determine pure components emission spectra for a unique set of spectra of mixtures in overdetermined conditions. On the other hand, it is also possible to extract pure components emission and excitation spectra of the only data corresponding to the 3D fluorescent spectrum of a single mixture. The results are evaluated in respect to noise level and concentrations ratio on both simulated and real spectra. | 18,966,973 |
Quantitative calibration of vapor levels of TNT, RDX, and PETN using a diffusion generator with gravimetry and ion mobility spectrometry. | A prototype generator for creating a continuous stream of explosive vapor was referenced quantitatively both to a standard weight from the National Institute of Standards and Technology (NIST) and to the response of an ion mobility spectrometer. Vapors from solid explosive, in a precision bore glass tube at constant temperature, diffuse into an inert gas flow. Mass output rates were determined by (1) sample temperature, and (2) sample tube dimensions (length and cross-sectional area). A reference to NIST was achieved gravimetrically though a microbalance calibrated with a reference weight; mass output rates were obtained for 2,4,6-trinitrotoluene (TNT), cyclotrimethylenetrinitramine (RDX) and pentaerythritol tetranitrate (PETN) at three or more oven temperatures between 79 degrees C and 150 degrees C. The mass output rate was stable over hundreds of hours of continuous operation and the output was adjustable from a few picograms per second to several nanograms per second through variation of the oven temperature. An independent calibration of the vapor generator for TNT at 79 degrees C using an ion mobility spectrometer matched exactly the gravimetric-based findings. In most instances, measured mass output rates compared favorably with theoretically calculated mass output rates, with discrepancies in a few cases resulting primarily from uncertainties in terms (vapor pressures and diffusion coefficients) used to perform the calculations. Agreement is generally not good for PETN, where molecular decomposition contributed to higher than expected measured mass outputs. | 18,966,981 |
Characterization of an enzyme linked immunosorbent assay for Aflatoxin B(1) based on commercial reagents. | Two indirect ELISA have been investigated for the determination of Aflatoxin B(1), employing only reagents commercially available, whose composition is not exactly known. In both cases the antigen (Aflatoxin B(1)-BSA) was coated to the solid phase (polystyrene microtiter plates). In one procedure the specific antibody was a conjugate with peroxidase, while in the other one it was not conjugated, and a second antibody labelled with alkaline phosphatase was used. A simple model was employed to characterize the equilibria, which is of help also if the exact composition of the immunoreagents is not known, and allows to predict the shape and position of the competition curve. The factors which determine the dynamic range were found to be the affinity constant the complex in the solid and the amount of antigen in the solid, and the affinity constant of the complex in solution phase. Useful aspects of the antigen-antibody complexation equilibria in the solid phase were investigated by ELISA at zero concentration of antigen in solution, obtaining c (s)c ( *) and K'f(n)(T). The equilibria in solution were studied by competition ELISA, obtaining K, the affinity constant of the antigen-antibody complex in solution. Similar results were obtained with the two procedures, for instance the affinity constant in solution was 2 x 10(8). A procedure for the determination of Aflatoxin B(1) in food samples was developed. | 18,966,984 |
Application of chelation ion chromatography to the determination of lanthanides in agriculture. | Lanthanides are widely present in soil and plant. In this paper, it is the first time that chelation ion chromatography is applied to analyse lanthanides in a series of samples in agriculture. This technique can eliminate bulk quantity of alkali, alkaline earth metals on chelating concentrator column (MetPac CC-1) and eliminate transition metals on cation exchange column (TMC-1) from complex matrices with ammonium acetate buffer while lanthanides are concentrated. It is shown to be capable of separating and determining all lanthanides on mixed-bed ion exchange column (CS5) in a wide variety of sample types with high accuracy. Elution is carried out with a concentration gradient of oxalic acid (Ox) and diglycolic acid (DGA), coupled with post-column spectrophotometric detection with 4-(2-pyridylazo)resorcinol (PAR) at 520 nm. It can determined ng ml(-1) scales of lanthanides. The whole run time after sample injection is about 55 min. | 18,966,987 |
Investigation of a flat sheet membrane desolvator for aqueous solvent removal with inductively coupled plasma atomic emission spectrometry. | Results obtained from a preliminary investigation of the performance of a flat sheet membrane desolvator (FSMD) utilizing dual hydrophobic polypropylene membranes with an average pore size of 0.05 mum and a 50 +/- 5 mum thickness are reported. The membranes have a desolvation area of 241 cm(2). The volume-to-surface area ratio is 0.3 cm. Using the FSMD with an ultrasonic nebulizer (USN), aqueous solvent desolvation efficiencies of greater than 99.9% were obtained at all nebulizer gas flow rates investigated (0.8, 1.2, and 1.8 l min(-1)). This efficient desolvation occurred when the countercurrent gas flow rate was equal to or slightly greater than the applied nebulizer gas flow rate. Under these conditions preconcentration factors of 18, 44, and 590 were observed with flows of 0.8, 1.2 and 1.8 l min(-1), respectively. Operating with countercurrent gas flow rates much higher than the nebulizer gas flow rates leads to a significant reduction in analyte flux, thus increasing detection limits. Depending on the nebulizer and countercurrent gas flow rate conditions, the FSMD contributed between 10-40% to the overall analyte loss in the system. The lowest detection limit observed for aqueous copper with the USN-FSMD system is 0.4 ppb at nebulizer and countercurrent gas flow rates of 1.2 and 1.4 l min(-1), respectively. At this nebulizer gas flow rate, replacing the FSMD in the system with a commercial tubular membrane desolvator, MDX100, gave a lowest Cu detection limit of 0.2 ppb at a countercurrent gas flow rate of 1.2 l min(-1). These detection limits represents improvements over the 0.7 and 8 ppb obtained with USN and pneumatic nebulization, respectively. | 18,966,989 |
Ion-selective electrode for bismuth(III) in ethylenediamintetraacetate medium. | A coated graphite-epoxy ion-selective electrode for bismuth(III), based on the ion-pair between the [Bi(EDTA)](-) anion and tricaprylylmethylammonium cation (Aliquat 336S) incorporated onto a poly(vinylchloride) (PVC) matrix is constructed. A thin membrane film of this ion-pair, dibutylphthalate (DBPh) or ortho-nitrophenyloctylether (o-NPOE) in PVC was deposited directly onto a Perspex(R) tube which contained a graphite-epoxy conductor substrate attached to the end of a glass tube. The coating solution was prepared by dissolving 30% (w/w) of PVC in 10 ml of tetrahydrofuran following addition of 65% (w/w) DBPh or o-NPOE and 5% (w/w) of the ionic pair. The effect of pH, EDTA concentration and some cation and anion on the electrode response is investigated. The bismuth(III) ion-selective electrode shows a linear response in the bismuth(III) concentration range from 1.0 x 10(-8) to 1.0 x 10(-1) mol 1(-1) and 1.0 x 10(-7) to 1.0 x 10(-1) mol 1(-1) and a slope of 56.8 and 59.2 mV dec.(-1) for the polymeric membranes containing DBPh and o-NPOE, respectively. The lifetime of this electrode was superior to 1 year (over 1600 determinations for each polymeric membrane), with practical detection limits of 6.3 x 10(-9) and 4.4 x 10(-8) mol 1(-1) with these plasticizers. Application of this electrode with bismuth(III) determination in a stomach anti-acid sample is described. | 18,966,999 |
The extraction of uranium by amidoximated orlon. | The nitrile groups in polyacrylonitrile (Orlontrade mark) fabric were converted to amidoxime groups to produce an amidoximated orlon fabric. The amidoximated fabric was evaluated for its ability to extract uranium from aqueous solution with a wide range of temperature and pH values. The conversion of nitrile groups to amidoxime groups was simple and relatively inexpensive. In general, the modified orlon fabric showed superior extractability of uranium at all temperatures and pH values tested when compared to untreated Orlontrade mark fabric. | 18,967,000 |
Potentiometric flow injection determination of amylase activity by using hexacyanoferrate(III)-hexacyanoferrate(II) potential buffer. | A highly sensitive potentiometric flow injection determination of amylase activity was carried out, utilizing a redox reaction of hexacyanoferrate(III) in alkaline media with reducing sugar as product of the enzymatic hydrolysis reaction of starch with amylase. The analytical method is based on the potential change detection of a flow-through type redox electrode detector due to the composition change of a [Fe(CN)(6)](3-)-[Fe(CN)(6)](4-) potential buffer solution, which is caused by the redox reaction with the product of the enzymatic reaction. A linear relationship exists between the potential change (peak height) and the activity of amylase. Amylase of a wide activity range from 2.5x10(-2) to 1.2x10(-4) U ml(-1) can be determined by the changing the concentrations of the [Fe(CN)(6)](3-)-[Fe(CN)(6)](4-) potential buffer from 10(-3) to 10(-5) M. The lower detection limit of amylase activity is 6.0x10(-5) U ml(-1). The sampling rate and relative standard deviation are 15 h(-1) and 0.9% (n=5) for 3.8x10(-3) U ml(-1) of amylase. The present method was successfully applied to determine amylase activity in real samples (commercial digestive medicines) with an accuracy of 4% compared with analytical results obtained using the present method with those achieved using the conventional titration method. | 18,967,038 |
Purification of metallothionein proteins from the crab, Portunus pelagicus-selectivity of hydrophobic interaction chromatography. | Both hydrophobic interaction chromatography (HIC) and ion-exchange chromatography (IEC) are commonly used for the purification of proteins as their mild elution conditions preclude the dangers of denaturation. Of the two methods, IEC which fractionates proteins on the basis of charge differences, exhibits a higher selectivity. In the case of the metallothionein (MT) proteins, the charge states of the proteins are very susceptible to change due to oxidation of the abundant thiol groups. This complicates fractionation with IEC. Separation using HIC, on the other hand, is based on the exposed hydrophobic groups, which remain relatively intact if the tertiary structure of the proteins is not disrupted. In this work, the successful isolation of two MT isoforms from the tropical crab species, Portunus pelagicus, using HIC serves to demonstrate the high selectivity of this technique, in addition to the fact that it is indifferent to the state of oxidation of the MT proteins during the purification procedure. | 18,967,051 |
AFM imaging and characterization of latex particles formed by copolymerization of styrene and poly(ethylene oxide) macromonomer. | A new type of latex particle was prepared by copolymerization of styrene and poly(ethylene oxide) macromonomer. By controlling the concentration of styrene in reaction mixtures, several latexes with different grain sizes were obtained. The packing patterns of the latex films as well as shapes and sizes of the latex particles were measured with atomic force microscopy (AFM). AFM images revealed that the grain sizes of the latexes increase with increasing concentration of styrene. At a higher styrene concentration (10 wt%), the latex showed a rather homogenous distribution of grain sizes. Lateral force microscopy (LFM) was used to reveal frictional features of latex particles. Contact and non-contact mode AFM were employed to image the same sample of the latex films. The results show that AFM working in non-contact mode can be used to effectively eliminate the horizontal-line-like artifacts, which may obscure AFM images. | 18,967,060 |
Use of time-resolved lanthanide-sensitized luminescence for the kinetic determination of p-aminobenzoic acid. | Lanthanide-sensitized luminescence was for the first time used to develop a simple kinetic method for the determination of p-aminobenzoic acid. The method is based on the formation of a complex with terbium(III) in the presence of trioctylphosphine oxide as synergistic agent and Triton X-100 as micellar medium. The high initial rate of the complex formation required the use of stopped-flow mixing technique in order to make kinetic measurements which, in addition, allows the method to be automated. Its analytical features compare very favourably with those described by using solid-surface room temperature phosphorescence in terms of rapidity, precision and selectivity. The initial rate is obtained within only 0.2 s after the reactants are mixed, which allows ready application of the proposed method to routine analyses. The calibration graph is linear over the range 0.08-4.0 mug ml(-1)p-aminobenzoic acid and the detection limit is 0.02 mug ml(-1). The relative standard deviation is close to 2%. The kinetic methodology avoids the effect of the sample matrix allowing the direct determination of this compound in pharmaceutical preparations. Analytical recoveries ranged between 98.6 and 113.0%. | 18,967,067 |
Sulphuric acid influence on liquid-liquid extraction of Co(II) and Zn(II) by MIBK from NH(4)SCN medium. | Liquid-liquid extraction of Co(II) and Zn(II) by methylisobutylcetone (MIBK) has been studied systematically from NH(4)SCN/H(2)SO(4) media. The influence of sulphuric acid concentration on the percentage of extraction of Co(II) and Zn(II) has been discussed. It is shown that sulphuric acid concentration has not the same effect on distribution curves of Co(II) and Zn(II). Thus, it is possible to have a separation of Zn(II) of Co(II) when [NH(4)SCN] is 0.5 mol l(-1) and [H(2)SO(4)] is about 2 mol l(-1). Under these conditions the separation factor (S(Zn/Co)) is around 580. The results are treated in terms of thermodynamic activities in aqueous phase, to determine the composition of the extracted complexes (M:SCN(-)) and to discuss the extraction mechanism. | 18,967,073 |
Transport of Cu(II) with hydroxamic acid through a liquid membrane. | N-Hydroxy-N-naphthylbenzamides (3) were synthesized for examining their ability to extract and transport Cu(II) through a liquid membrane. The transport was proton-driven and was capable of moving metal ions ;up-hill'. Thus, it was possible to follow the transfer of Cu(II) from the aqueous source phase to the organic layer and from the organic layer to the receiving phase. The N-hydroxy-N-(2-naphthyl)benzamide (3b) carrier displayed much more remarkable selectivity for Cu(II) compared with N-hydroxy-N-(1-naphthyl)benzamide (3a). This difference in selectivity was explained in terms of the stability of the Cu(II) complex in chloroform. | 18,967,085 |
Simultaneous determination of propranolol and pindolol by synchronous spectrofluorimetry. | The simultaneous determination of propranolol and pindolol using synchronous fluorescence spectrometric techniques is described. The method involves measuring the natural fluorescence of these drugs in a 50% (v/v) ethanol-water medium using zero and first derivative synchronous spectrofluorimetry. Under the optimum conditions, the linear determination ranges of propanolol and pindolol are ca. 0.02-1.0 and 0.04-1.2 mug ml(-1), respectively. The results showed that propranolol and pindolol can be determined simultaneously when the concentration ratio of propranolol to pindolol varies from 1:100 to 50:1 in the mixed sample. The method has been satisfactorily applied to the determination of propranolol and pindolol in urine samples and propranolol in pharmaceutical preparations. | 18,967,086 |
Multivariate calibration applied to synchronous fluorescence spectrometry. Simultaneous determination of polycyclic aromatic hydrocarbons in water samples. | Synchronous fluorescence spectra of mixtures containing ten polycyclic aromatic hydrocarbons (anthracene, benz[a]anthracene, benzo[a]pyrene, chrysene, fluoranthene, fluorene, naphthalene, perylene, phenanthrene and pyrene) have been used for the determination of these compounds by Partial Least Squares Regression (PLSR), using both PLS-1 and PLS-2. Different procedures have been used for the pretreatment of the data in order to obtain better models, and the size of the calibration matrix has also been studied. The best models have been used for the determination of the above mentioned PAHs in spiked natural water samples at concentration levels between 4 and 20 ng ml(-1). Recoveries ranged from 80 to 120% in most cases, although fluorene gave significantly lower results. | 18,967,097 |
Chemiluminescent determination of pyridoxine hydrochloride in pharmaceutical samples using flow injection. | A chemiluminescent method using flow injection is described for the determination of pyridoxine hydrochloride. Its detection limit, linearity and reproducibility were examined. The method is based on the enhancing effect of pyridoxine hydrochloride on the chemiluminescence generated by the oxidation of luminol with hydrogen peroxide in aqueous potassium hydroxide and sodium oxalate. The proposed method is simple and inexpensive. The chemiluminescence intensity is a linear function of pyridoxine hydrochloride concentration over the range 10-250 mug ml(-1) with a detection limit of 6 mug ml(-1). The applicability of the method was demonstrated by the determination of pyridoxine hydrochloride in different tablet formulations and some dietary sources. | 18,967,105 |
Determination of aluminium and manganese in human scalp hair by electrothermal atomic absorption spectrometry using slurry sampling. | Methods for the determination of aluminium and manganese in human scalp hair samples by electrothermal atomic absorption spectrometry using the slurry sampling technique were developed. Palladium and magnesium nitrate were used as chemical modifiers. Hair samples were pulverized using a zirconia vibrational mill ball, and were prepared as aqueous slurries. Determinations can be performed in the linear ranges of 1.9-150 mug l(-1) Al(3+) and 0.03-10.0 mug l(-1) Mn(2+). Limits of detection of 0.9 mg kg(-1) and 27.6 mug kg(-1) were obtained for aluminium and manganese, respectively. The analytical recoveries were between 99.6 and 101.8% for aluminium and in the 98.3-101.3% range for manganese. The repeatability of the methods (n=11), slurry preparation procedure and ETAAS measurement, was 16.0 and 7.9% for aluminium and manganese, respectively. The methods were finally applied to the aluminium and manganese determination in 25 scalp hair samples from healthy adults. The levels for aluminium were between 8.21 and 74.08 mg kg(-1), while concentrations between 0.03 and 1.20 mg kg(-1) were found for manganese. | 18,967,107 |
Use of zirconium oxychloride to neutralize HF in the microwave-assisted acid dissolution of ceramic glazes for their chemical analysis by ICP-OES. | The use of a zirconium compound (ZrOCl(2)) to neutralize HF in the microwave-assisted acid dissolution of ceramic glazes for their chemical analysis was tested. Zr is a strong complexing agent for the fluorine ion and permits the determination of those elements which would form insoluble fluorides. The use of Zr implies strong spectral interferences and a high salt content; however, we found that at least 27 elements can be measured with low detection limits, and satisfactory precision and accuracy. In addition, the use of ZrOCl(2) would permit the complete analysis of a ceramic glaze with a single attack when acid-resistant mineral phases are not present. For potassium determinations in acid matrix, the addition of an ionization buffer was studied in order to increase sensitivity, avoiding ionization interferences and non-linear calibration curves. | 18,967,112 |
Possibilities for speciation of Al-citrate and other negatively charged Al complexes by anion-exchange FPLC-ICP-AES. | An anion-exchange fast protein liquid chromatographic-inductively coupled plasma atomic emission spectrometric procedure (FPLC-ICP-AES) was developed for speciation of Al-citrate and other negatively charged Al complexes. FPLC separations were carried out on a Mono Q HR 5/5 strong anion-exchange FPLC column over a pH range from 3.5 to 11.0. An aqueous-NaNO(3) (4 mol dm(-3)) linear gradient elution was applied over 10 min for separation of a particular Al species. The separated Al species were determined in 0.5 cm(3) eluate fractions ;off line' by ICP-AES. Under optimal analytical procedures Al-citrate was separated from Al-oxalate and Al-EDTA in a neutral pH range. Good reproducibility of the FPLC-ICP-AES procedure was obtained for determination of a particular Al species at optimal measurement conditions (RSD +/-2%). Al(3+) and neutral Al-citrate species were strongly adsorbed on the column resin and did not interfere with the separation of negatively charged Al complexes. Al(OH)(4)(-) species were separated from Al-citrate in an alkaline pH region, but quantitatively determined only at a pH of 11.0. The distribution of Al species over a pH range from 3.5 to 11.0 agreed with the reported calculated data. The limit of detection (3sigma basis) for separated Al species was 0.1 mug cm(-3). | 18,967,147 |
Analysis for metallothioneins using coupled techniques. | Analytical chemistry of metallothioneins based on the coupling of a high resolution separation technique with an element or species selective detection technique is discussed. The role of size-exclusion chromatography (SEC) with on-line atomic spectrometric detection for the quantification of metallothionein fraction in cell cytosols is evaluated. Particular attention is given to the conditions for the separation of metallated metallothionein isoforms (MT-1, MT-2, MT-3) and sub-isoforms within these classes by anion-exchange and reversed-phase HPLC. Techniques for interfacing chromatography with atomic absorption spectrometry (AAS), inductively coupled plasma atomic emission spectrometry (ICP AES) and ICP mass spectrometry (MS) are assessed. The potential of electrospray (tandem) mass spectrometry for the characterization of metallothionein isoforms with respect to molecular mass and aminoacid sequence is highlighted. Perspectives for capillary zone electrophoresis (CZE), microbore and capillary HPLC with ICP MS and electrospray MS(/MS) detection for the probing of metallothioneins are discussed. Applications of hyphenated techniques to the analysis of real-world samples are reviewed. | 18,967,150 |
Use of microwave digestion for estimation of heavy metal content of soils in a geochemical survey. | A procedure for the rapid and safe analysis of soils with widely differing organic matter contents has been investigated and validated. Surface soils, totalling 295 and sampled on a grid basis, representing 22% of the land-base of the Republic of Ireland, have been analysed for cadmium, chromium, copper, nickel, lead and zinc. Soil concentrations of cadmium, chromium, lead and nickel exhibit patterns of regionalised elevation. Implications of this elevation are considered in relation to sewage sludge application to land, future requirement for baseline surveys and concerns over concentrations in food products. | 18,967,164 |
Sensitivity and selectivity of electrochemical enzyme sensors for inhibitor determination. | The performance of electrochemical biosensors developed for the determination of inhibiting species is considered. The role of various factors affecting the analytical characteristics of biosensors, their selectivity toward inhibitors to be tested as well as operational characteristics is discussed. The choice of enzyme-inhibitor system, the influence of enzyme immobilization on the behaviour of a biosensor, the modes of the optimization of working conditions are discussed. Most conclusions are illustrated with the models of the application of biosensors for monitoring environmental pollutants. | 18,967,167 |
Extraction of phenols using polyurethane membrane. | The extraction of various phenols from aqueous and organic solutions using polyurethane membrane has been investigated. The effects of solution concentration, extraction time, surface area, pH, salts, and temperature on extraction were studied. The phenols are extracted as neutral species and the extraction is governed by a combined effect of intra- and intermolecular hydrogen bonding and nonspecific hydrophobic interactions. The ether-type membrane showed higher extraction capability for the phenols than the ester-type polyurethane membrane. | 18,967,171 |
Determination of trace europium based on new fluorimetric system of europium(III) with thenoyltrifluoroacetone and N,N'-dinaphthyl-N,N'-diphenyl-3,6-dioxaoctanediamide. | In the present paper, N,N'-dinaphthyl-N,N'-diphenyl-3,6-dioxaoctanediamide acts as a specific reagent for enhancing the fluorescence intensity of Eu(III) complex with thenoyl trifluoroacetone (TTA), the spectrofluorimetric determination of trace amounts of Eu(III) based on the above system was carried out and its luminescence mechanism was studied. The excitation and emission wavelengths are 343.6 and 613.3 nm, respectively. The fluorescence intensities vary linearly with the concentration of europium(III) in the range 3.647x10(-3)-3.039 mug ml(-1) for the original fluorescence with a detection limit down to 2.279x10(-4) mug ml(-1) and the standard deviation is 0.063 mug ml(-1) for 10 times measurements, and in the range 7.598x10(-4)-0.0243 mug ml(-1) (SD=0.035 for 15 times measurements), 0.06078-0.6100 mug ml(-1) (SD=0.52 for 10 times measurements) for the first derivative fluorescence signal with a detection limit down to 8.566x10(-5) mug ml(-1). The interferences of other rare earths and some of inorganic ions are described. This method is a direct, rapid, selective and sensitive analytical method for the determination of trivalent europium in rare earth ore samples and high purity of rare earth oxides. | 18,967,173 |
Spectrophotometric determination of methyldopa and dopamine in pharmaceutical formulations using a crude extract of sweet potato root (Ipomoea batatas (L.) Lam.) as enzymatic source. | A rapid, precise and low cost spectrophotometric method is proposed for the determination of methyldopa and dopamine in pharmaceutical formulations. The crude extract of sweet potato root (Ipomoea batatas (L.) Lam.) was used as an enzymatic source of polyphenol oxidase (PPO; EC.1.14.18.1). This enzyme catalyses the oxidation of catecholamines to the corresponding methyldopaquinone and dopaminequinone. Those compounds are converted by a rapid spontaneous auto-oxidation to methyldopachrome and dopaminechrome which have a strong absorption at 480 or 470 nm, respectively. The calibration graphs are linear from 2.0x10(-4) to 6.0x10(-3) M. The results obtained by the proposed enzymatic method are in close agreement with those obtained using a Pharmacopoeia procedure and also with the label values. The detection limit (three times the signal blank/slope) was 3.4x10(-5) and 3.0x10(-5) M for methyldopa and dopamine, respectively, the recovery of methyldopa and dopamine from three samples ranged from 97.5 to 102.9% of the added amount. | 18,967,177 |
Direct determination of copper and zinc in cow milk, human milk and infant formula samples using electrothermal atomization atomic absorption spectrometry. | Infant formula and powdered milk samples were suspended in a medium containing 20% ethanol, 0.65% nitric acid, 6% hydrogen peroxide and 0.1% ammonium dihydrogenphosphate and directly introduced in the electrothermal atomizer. Liquid milk samples were diluted with this suspension solution. The build-up of carbonaceous residues inside the atomizer was avoided by using a combination of hydrogen peroxide and nitric acid. Fast programs were used to simplify the heating cycles. Calibration was carried out using aqueous standards and the detection limits for copper and zinc were found to be 70 and 15 pg, respectively. The metal contents of several milk samples obtained by direct introduction of the samples agree with those obtained by means of a conventional procedure based on the total dissolution of the samples. The reliability of the methods was also confirmed by analyzing three certified reference materials. The free and protein binding fractions were measured by ultrafiltration membrane permeability of the milk samples. | 18,967,184 |
Methods for determination of hexachlorobenzene and pentachlorophenol in soil samples. | The efficiency of methods for the determination of hexachlorobenzene (HCB) and pentachlorophenol (PCP) in soil samples was evaluated. An on-line method was applied for HCB determination. Soil samples were transferred to chromatographic columns prepacked with alumina. The HCB elution was processed with n-hexane. The PCP was extracted from soil samples with n-hexane-acetone in an ultrasonic bath. After re-extraction with K(2)CO(3) solution PCP was acetylated with acetic anhydride. The pentachlorophenyl acetate derivative was then extracted with n-hexane. The HCB and PCP derivative were analyzed by gas chromatography with electron capture detection (GC-ECD). Mean recoveries obtained from soil samples fortified at levels of 0.5; 4 and 20 ng g(-1), ranged from 91 to 100% for HCB, and for PCP, at levels of 10; 40 and 200 ng g(-1), ranged from 88 to 101%. These results demonstrated the efficiency of the proposed methods. | 18,967,213 |
Complexation of trivalent cations (Al(III), Cr(III), Fe(III)) with two phosphonic acids in the pH range of fresh waters. | The complex formation constants of two phosphonic acids, HEDP and ATMP, with three trivalent metallic cations, Al(III), Cr(III) and Fe(III), have been determined by acid-base titration at 25 degrees C and constant ionic strength (0.1 mol l(-1), KNO(3)), using Martell and Motekaitis' computer programs. Species distribution curves showed that all three cations are in complex form in the pH range of fresh waters (5-9). The study of different cation/ligand ratios proved that both ligands mainly form anionic soluble complexes for systems having an excess of ligand-as protonated and unprotonated forms and especially ternary complexes with HEDP. For higher metal concentrations (excess of cation), weakly soluble species of HEDP and ATMP were formed with Al(III) and Cr(III). Two insoluble complexes with ATMP have been identified by SEM/EDAX as AlH(3)X((s)) and Cr(2)X((s)). Regarding Fe(III) species, Fe(OH)(3(s)) precipitate seems to predominate in solution. | 18,967,224 |
Multivariate analysis of Cd(II), In(III), Tl(I) and Pb(II) in mixtures using square wave anodic stripping voltammetry. | Accurate qualitative and quantitative results were obtained by the application of parameter estimation methods, viz. Classical Least Squares ;CLS', Inverse Least Squares ;ILS' and Kalman Filter ;KF' algorithms. These methods were used to separate strongly overlapping electrochemical peaks produced by binary, ternary and quaternary mixtures of traces of cited poisonous heavy metals stripped from the hanging mercury drop electrode in an acetate-bromide electrolyte using the square wave anodic stripping voltammetry. The analysis was achieved using a single standard addition, the concentrations studied were down to 50 nM and molar ratios up to 1:6 for binary mixtures. A statistical analysis of the results was reported. The method was applied for the ultratrace analysis of the cited cations in a sample of sodium hydrogen carbonate AR. | 18,967,246 |
Microcoated wire sensors for the determination of anticancer drugs cyclophosphamide and ifosphamide in the presence of their degradates. | The construction and electrochemical response characteristics of poly (vinyl chloride) and poly (vinyl chloride) carboxylate membrane sensors for the determination of cyclophosphamide and ifosphamide are described. Based on the formation of an ion-pair complex between the drug cation and sodium tetraphenylborate, two poly (vinyl chloride) sensors, namely a cyclophosphamide membrane sensor and ifosphamide membrane sensor were fabricated. They show a linear response for both drugs over the concentration range 10(-2)-10(-4) M with cationic slopes of 56 and 54.6 mV per concentration decade, for sensor 1 and sensor 2, respectively. Based on the interaction between the drug solution and the dissociated COOH groups in the poly (vinyl chloride) carboxylate, sensor 3 was fabricated. It shows a linear response for both drugs over the concentration range 10(-3)-10(-5) M with a cationic slope of 49.7 mV per concentration decade. The direct potentiometric determination of cyclophosphamide and ifosphamide in their pharmaceutical preparations using the proposed sensors gave average recoveries of 101.3+/-0.6, 100.8+/-10.7 and 102.0+/-11.0% for the sensors 1, 2 and 3, respectively, which compares reasonably well with the data obtained using the British Pharmacopoeial method (1993). Sensors 1 and 2 were also used to follow up the stability of the drugs studied in the presence of their degradates. These degradation products have no diverse effect on the responses of sensors 1 and 2. | 18,967,269 |
Screen-printed voltammetric sensor for TNT. | Screen-printed carbon electrodes have been developed as disposable voltammetric sensors for 2,4,6-trinitrotoluene (TNT). Thick-film electrodes based on various conventional and modified inks have been compared for this task. The operation is based on placing the selected thick-film carbon sensor in the non-deaerated/quiescent sample and using a fast (<1 s) and sensitive square-wave voltammetric scan. Different experimental variables have been optimized to yield a detection limit of 200 ppb TNT and a wide linear range. The high selectivity, demonstrated in assays of various untreated environmental samples, is attributed to the facts that the reducible nitro group is rare in nature and that most electroactive organic compounds require higher potentials. The new single-use sensor strips should facilitate the on-site environmental screening of TNT. | 18,967,270 |
Quantitative separation of zinc traces from cadmium matrices by solid-phase extraction with polyurethane foam. | A system for separation of zinc traces from large amounts of cadmium is proposed in this paper. It is based on the solid-phase extraction of the zinc in the form of thiocyanate complexes by the polyurethane foam. The following parameters were studied: effect of pH and of the thiocyanate concentration on the zinc extraction, shaking time required for quantitative extraction, amount of PU foam necessary for complete extraction, conditions for the separation of zinc from cadmium, influence of other cations and anions on the zinc sorption by PU foam, and required conditions for back extraction of zinc from the PU foam. The results show that zinc traces can be separated from large amounts of cadmium at pH 3.0+/-0.50, with the range of thiocyanate concentration from 0.15 to 0.20 mol l(-1), and the shaking time of 5 min. The back extraction of zinc can be done by shaking it with water for 10 min. Calcium, barium, strontium, magnesium, aluminum, nickel and iron(II) are efficiently separated. Iron(III), copper(II) and cobalt(II) are extracted simultaneously with zinc, but the iron reduction with ascorbic acid and the use of citrate to mask copper(II) and cobalt(II) increase the selectivity of the zinc extraction. The anions nitrate, chloride, sulfate, acetate, thiosulphate, tartarate, oxalate, fluoride, citrate, and carbonate do not affect the zinc extraction. Phosphate and EDTA must be absent. The method proposed was applied to determine zinc in cadmium salts using 4-(2-pyridylazo)-resorcinol (PAR) as a spectrophotometric reagent. The result achieved did not show significant difference in the accuracy and precision (95% confidence level) with those obtained by ICP-AES analysis. | 18,967,283 |
Glutathione oxidase-like activity of glass beads, silica gel and anion-exchange resin modified with cobalt(III)-tetrakis(4-carboxyphenyl)porphine. | Silica gel and glass beads were modified by using acid chloride of metal-tetrakis(4-carboxyphenyl)porphine (M-TCPP) through a peptide bond, and an anion-exchange resin with M-TCPP by ion-exchange reaction and physical adsorption. The carriers modified with Co(3+)-TCPP proved to accelerate the redox reaction which is catalyzed by glutathione oxidase (GSHOx), while those modified with Mn(3+)-TCPP exhibited no activity. Formation of GS-SG and hydrogen peroxide was confirmed by means of mass spectroscopy and colored reaction, respectively. The silica gel modified with Co(3+)-TCPP exhibited the strongest activity among the tested carriers, and was expected to be useful practically as a solid catalyst for the determination of glutathione. | 18,967,291 |
Transport and separation of Ag(+) and Zn(2+) by donnan dialysis through a monovalent cation selective membrane. | Donnan Dialysis of Ag(+) and Zn(2+) was investigated through a cation exchange membrane (CMS Neosepta) when a proton concentration difference was maintained between the two sides of the membrane. Developed for the production of brine from sea water, CMS Neosepta showed a higher permeability to monovalent than to bivalent cations. Several physico-chemical parameters have been determined (electrical resistance, membrane potential, sorption of electrolytes, Zn(2+) and Ag(+) diffusion coefficients). The flux of Ag(+) and the diffusion potential in the membrane increase with HNO(3) concentrations. Ag(+) and Zn(2+) can be separated because of the preferential membrane transfer for Ag(+). | 18,967,293 |
pH-Metric determination of acid numbers in petroleum oils without titration. | A new pH-metric method without titration has been developed for determination of acid numbers lower than 0.1 mg (KOH) g(-1) (oil) in petroleum oils such as White, Transformer and Basic oils. The method is based on rapid and complete extraction of acids from an oil test portion into the novel reagent and measurement of the conditional pH in the ;oil-reagent' mixture by a glass electrode. The method has a quantitation limit equal to 1x10(-3) mg (KOH) g(-1) (oil), uses non-toxic reagents, is not time and labor consuming, and is cheap and simple for automation. | 18,967,302 |
Simultaneous determination of copper, cadmium and nickel by ratio derivative polarography. | Ternary mixtures of metals can be resolved by using the ratio derivative polarography without the need for any pre-separation step. The method is based on the simultaneous use of the first derivative of ratios of polarograms and measurements of zero-crossing potentials. The polarogram of the mixture is obtained and the amplitudes of the current at appropriate potentials are divided by the corresponding amplitudes in the polarogram of a standard solution of one of the components, and the subsequent derivation against potential results to the first derivative of the ratio polarogram. The concentrations of the other two components are then determined from their respective calibration graphs established by measuring the ratio derivative analytical signal at the selected zero-crossing points. The method has been successfully applied for resolving ternary mixtures of copper, cadmium and nickel, which have overlapped polarograms in pH 2.87 Britton-Robinson buffer. The concentration ranges to be determined are 0.30-1.40 mg l(-1) for copper, 0.90-4.50 mg l(-1) for cadmium and 0.20-1.20 mg l(-1) for nickel, and the recoveries are 88.3-101.9% for copper, 92.2-105.4% for cadmium and 95.0-107.0% for nickel. | 18,967,312 |
Rapid detection of Escherichia coliform with a bulk acoustic wave sensor based on the gelation of Tachypleus amebocyte lysate. | A new sensing method (BAW-TAL technique), which combined the bulk acoustic wave (BAW) technique with the gelation reaction of Tachypleus amebocyte lysate (TAL), was used for viscosity and density measurement and applied to the detection of Escherichia coliform (E. coli). This method depended on the fact that the viscosity and density of the mixture increased, and as a result, the resonance frequency decreased correspondingly after TAL was mixed with the heated E. coli solution that contained endotoxin. Results showed that the frequency shift was linearly related to the logarithm of E. coli concentration in the range of 2.7x10(4)-2.7x10(8) cells/ml. The correlation coefficient was 0.996. This BAW-TAL method was compared with the standard pour plate counts (PPC) method. The proposed method was much more rapid and simpler for detection of E. coli than the traditional methods. | 18,967,327 |
Kinetic determination of trace cobalt(II) by visual autocatalytic indication. | A highly sensitive and simple visual autocatalytic method has been developed for the determination of trace cobalt. The cobalt ion released by the oxidative decomposition of inert bis[2-(5-bromo-2-pyridylazo)-5-(N-propyl-N-sulfopropyl-amino-phenolato] cobaltate (Co(III)-5-Br-PAPS) with peroxomonosulfate acts as a catalyst for the oxidative degradation of the complex. Thus a definite time lapse of degradation is observed by the sudden disappearance of colored Co(III) complexes. The degradation time varies inversely with the logarithm of the initial concentration of cobalt(II). The determination range of cobalt(II) was from 3x10(-9) to 2x10(-7) M in the presence of 5x10(-6) M of 5-Br-PAPS. The relative standard deviation of the spot size method (10 mul) was 3.5% at 1x10(-7) M cobalt(II). This autocatalytic indicator reaction system has been successfully applied for the visual determination of urinary cobalt. | 18,967,335 |
Flow-injection catalytic spectrophotometric determination of nitrite using the redox reaction between naphthol green B and potassium bromate. | A flow injection catalytic spectrophotometric method is proposed for the determination of nitrite based on its catalytic effect on the redox reaction between naphthol green B and potassium bromate in phosphoric acid medium. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of naphthol green B at the maximum absorption wavelength of 722 nm. The detection limit is 0.5 ng cm(-3) in a sample volume of 90 mm(3). Up to 50 samples can be analyzed per hour with a relative precision of ca. 2%. The method is free from most interferences, especially from large amounts of nitrate. The procedure was successfully applied to the determination of trace nitrite in natural waters. | 18,967,351 |
Analysis of binary mixtures of flufenamic, meclofenamic and mefenamic acids by derivative synchronous fluorescence spectrometry. | Second-derivative synchronous fluorescence spectrometry was used to develop a simple, rapid and sensitive spectrofluorimetric method for the determination of binary mixtures of the nonsteroidal antiinflammatory drugs flufenamic (FFA), meclofenamic (MCFA) and mefenamic (MFA) acids in serum and pharmaceutical formulations. The method is based on the intrinsic fluorescence of these compounds in chloroform. A Deltalambda=105 nm was used for the resolution of FFA-MFA and MFA-MCFA mixtures, whereas the FFA-MCFA mixture was determined at Deltalambda=40 nm. Serum samples are treated with trichloroacetic acid to remove the proteins, and the analytes are extracted in chloroform prior to determination. Pharmaceutical preparations were analysed without prior separation steps. | 18,967,356 |
The effect of polymeric supports and methods of immobilization on the performance of an optical copper(II)-sensitive membrane based on the colourimetric reagent Zincon. | A comparative study on the effect of different immobilization methods and matrix materials on the performance of copper(II)-sensitive membrane layers is presented. The indicator dye Zincon was immobilized in hydrophilic and hydrophobic polymers by various methods including: (a) physical entrapment of the Zincon-tetraoctylammonium ion pair in plasticized PVC, hydrogel, polystyrene, ethyl cellulose, poly-HEMA, AQ-polymer and in sol-gel glass; (b) electrostatic immobilization on an anion exchanger cellulose; and (c) covalent immobilization on cellulose via a sulfatoethylsulfonyl reactive group. The response to copper(II) ion was evaluated kinetically via the initial slope of the change in absorbance within 1 min. Layers made of hydrogel and PVC provide the highest sensitivity, while covalent immobilization is the most reproducible one, and sol-gel layers display the best mechanical stability. | 18,967,361 |
Electrochemical detection of lectin using a galactosamine labeled with daunomycin. | To detect a lectin from soybean, an electrochemical procedure was developed by the use of a labeling of galactosamine. Because the lectin has binding sites to galactosamine, galactosamine labeled with daunomycin having electroactivity was prepared. When labeled galactosamine (LG) combines with lectin, the part of daunomycin is taken in the binding sites of the lectin and becomes electroinactive. Therefore, the concentration of the lectin can be estimated by measuring the peak current of the LG. On the other hand, a competitive reaction to the lectin of galactosamine and the LG makes a detection of galactosamine possible. This method has merit that does not require a separation procedure of the free LG from the bound one. An effect of length of spacer between daunomycin and galactosamine was also investigated. It was found that adsorption of reagent on the electrode increased due to introduction of the spacer. Furthermore, the electrode response of the LG was influenced by the type of the spacer. | 18,967,370 |
Influence of interfering dissolved organic matter on the determination of hydrogen peroxide by a colorimetric method based on the peroxidase catalyzed oxidation of N,N-diethyl-p-phenylenediamine. | The influence of dissolved organic matter (DOM), such as humic acid (HA) and hydroxybenzoic acids, on the determination of H(2)O(2) via a colorimetric method using N,N-diethyl-p-phenylenediamine (DPD) was examined. The influence of DOM on absorbance decay at 551 nm, which represents the wavelength for maximum absorption of the oxidized species of DPD (DPD(+)), were investigated in detail. Significant decrease in the absorbance at 551 nm was observed in the presence of HA and gallic acid. This resulted in a fadeout of the purple color of DPD(+), which, in term, created great difficulties in the measurement of H(2)O(2) in solutions which contain DOM. To remove DOM prior to the addition of coloring reagents, a diethylaminoethyl Sephadex A-25 ion exchanger was used prior to the analysis for pre-separation. It was found that this pre-separation was useful in the DPD colorimetric determination of H(2)O(2) the solution which contain DOM. | 18,967,396 |
Decomposition mechanism of an artemisinin-type compound via hemin-electrocatalysis. | The interaction between a typical derivative of artemisinin and hemin was investigated by electrochemical and spectroelectrochemical methods. This derivative can be reduced via hemin-catalysis at the glassy carbon electrode, the cathodic overpotential is decreased by ca. 650 mV. A HPLC method for separating the products of the catalytic reaction was established. They were identified either in H(2)O-CH(3)CN solution or in tetrahydrofuran, respectively. The structures of these products show that the hemin-catalyzed decomposition of an artemisinin-type compound on the glassy carbon or reticulated vitreous carbon electrode can be achieved by both electrochemical reduction and rearrangement. The conclusion that the reaction of artemisinin with hemin is a critical step in the antimalarial mechanism of artemisinin can be drawn. | 18,967,453 |
Determination of low molecular weight organic acids in soil solution by HPLC. | An HPLC method employing an ion exclusion column was developed for the determination of low molecular weight organic acids in soil solution. The method includes extensive sample pretreatment using ultrafiltration and cation exchange. The method showed linear calibration graphs (r>0.99) and the limits of detection in the range 0.1-26 muM. The recovery of eleven added acids ranged from 89 to 102%. Soil solutions of five horizons of a podzolised soil were analysed. The results showed that these compounds made up 1-3% of the dissolved organic carbon and 0-14% of the acidity. Identification of the major acids was also carried out by capillary zone electrophoresis. | 18,967,456 |
Modification of iodometric determination of total and reactive sulfide in environmental samples. | In iodometric determination of sulfide two reactions are taking place when alkaline solution is added to HCl acid-iodine. The main oxidation reaction (1), H(2)S+I(2)=2HI+S; and side reaction of sulfide (2), S(-2)+4I(2)+8OH(-)=SO(4)(2-)+8I(-)+4H(2)O. Preference of reaction (2) over (1) is dependent on pH increasing to >7. When sulfide solution of pH 9 was mixed with HCl acid-iodine, the recovery exceeded 120%, but the recovery of a solution with a pH of 13 exceeded 200%. To eliminate the side reaction in iodometric titration, the sulfide solution must be acidic when it is mixed with HCl-iodine. To avoid the side reaction (2), the pH of sulfide solutions were adjusted with acetic acid to pH 5.5, mixed with HCl-iodine solution and then titrated with standard thiosulfate with precision and accuracy <+/-3%. | 18,967,472 |
A novel biosensor for specific determination of hydrogen peroxide: catalase enzyme electrode based on dissolved oxygen probe. | A biosensor for the specific determination of hydrogen peroxide was developed using catalase (EC 1.11.1.6) in combination with a dissolved oxygen probe. Catalase was immobilized with gelatin by means of glutaraldehyde and fixed on a pretreated teflon membrane served as enzyme electrode. The electrode response was maximum when 50 mM phosphate buffer was used at pH 7.0 and at 35 degrees C. The biosensor response depends linearly on hydrogen peroxide concentration between 1.0x10(-5) and 3.0x10(-3) M with a response time of 30 s. The sensor is stable for >3 months so in this period >400 assays can be performed. | 18,967,474 |
Quantitative measurements of ammonium, hydrogenophosphate and Cu(II) by diffuse reflectance spectrometry. | Diffuse reflectance spectrometry is shown to be useful for the quantitative determination of small amounts of pollutants. The relation between sample concentration and reflectance is described by the Kubelka-Munk equation. The experiments were performed with a laboratory constructed diode array spectrophotometer. We can obtain the quantitative reflectance values of different precipitates like ammonium with Nessler's reagent, hydrogenophosphate with silver nitrate and a complex such as Cu(II) with dithiooxamide 'rubeanic acid' by forming a spot colour on filter paper. We have obtained for each reagent a calibration curve by plotting the relative intensity of reflectance versus the log of the mol (dm(3))(-1) concentration. The linearity was obtained for Cu(II) from 8x10(-4) to 2.5x10(-2) mol l(-1) with r(2)=0.9838 and from 10(-3) to 10(-1) mol l(-1) for polyphosphate with r(2)=0.9975 and from 5x10(-4) to 5x10(-2) mol l(-1) for ammonium with r(2)=0.9889. We can consider that for a direct measurement of the intensity of reflectance, it is possible to perform quantitative spot-test analysis. | 18,967,477 |
Determination of methylamphetamine and related compounds in human urine by high performance liquid chromatography/electrospray/mass spectrometry. | A study of liquid chromatography/electrospray/mass spectrometry (LC/ES/MS) for the determination of methylamphetamine and related compounds (amphetamine, ephedrine, phenylpropanolamine) in human urine was undertaken. We assessed the effect of collision induced dissociation (CID) spectra generated by varying exit voltage of capillary and skimmer. The responses of ES/MS in different mobile phase and the effects of mobile phase modifier were examined. An isocratic LC method using methanol/water (80/20) and acetic acid (0.001%) as a modifier to separate these compounds was developed. Microporous ultrafiltration technique was employed to pre-treat urine sample prior to LC/ES/MS analysis. Good recoveries for methylamphetamine and amphetamine were determined as well as linearity, detection limit and precision associated with this method were determined. Drug spiked urine samples and urine samples of methylamphetamine addicts were successfully measured by this newly developed method. | 18,967,481 |
Evaluation of luminol-H(2)O(2)-KIO(4) chemiluminescence system and its application to hydrogen peroxide, glucose and ascorbic acid assays. | A novel chemiluminescence (CL) system was evaluated for the determination of hydrogen peroxide, glucose and ascorbic acid based on hydrogen peroxide, which has a catalytic-cooxidative effect on the oxidation of luminol by KIO(4). Hydrogen peroxide can be directly determined by luminol-KIO(4)-H(2)O(2) CL system. The detection limit was 3.0x10(-8) mol l(-1) and the calibration graph was linear over the range of 2.0x10(-7)-6.0x10(-4) mol l(-1). The relative standard deviation of H(2)O(2) was 1.1% for 2.0x10(-6) mol l(-1) (N=11). Glucose was indirectly determined through measuring the H(2)O(2) generated by the oxidation of glucose in the presence of glucose oxidase at pH 7.6. The present method provides a source for H(2)O(2), which, in turn, coupled with the luminol-KIO(4)-H(2)O(2) CL reaction system. The CL was linearly correlated with glucose concentration of 0.6-110 mug ml(-1). The relative standard deviation was 2.1% for 10 mug ml(-1) (N=11). Detection limit of glucose was 0.08 mug ml(-1). Ascorbic acid was also indirectly determined by the suppression of luminol-KIO(4)-H(2)O(2) CL system. The calibration curve was linear over the range of 1.0x10(-7)-1.0x10(-5) mol l(-1) of ascorbic acid. The relative standard deviation was 1.0% for 8.0x10(-7) mol l(-1) (N=11). Detection limit of ascorbic acid was 6.0x10(-8) mol l(-1). These proposed methods have been applied to determine glucose, ascorbic acid in tablets and injection. | 18,967,485 |
Determination of rare earth impurities in high purity gadolinium oxide by inductively coupled plasma mass spectrometry after 2-ethylhexylhydrogen-ethylhexy phosphonate extraction chromatographic separation. | A method was developed for the determination of rare earth impurities in high purity Gd(2)O(3) by inductively coupled plasma mass spectrometry (ICP-MS). The matrix suppression effect of Gd(2)O(3) on signals of rare earth impurities was compensated for by Re internal standardization. The spectra overlap interferences from GdH, GdO, GdOH(n) (n=1-3) on Tb, Tm, Yb and Lu were eliminated by 2-thylhexylhydrogen-2-ethylhexy phosphonate (EHEHP) extraction chromatographic separation. The detection limits for REEs were 0.005-0.017 ng ml(-1) in solution and 0.002-0.05 mug g(-1) in solid. Recoveries of spiked sample for REEs were from 88 to 121% with the precision of 1.0-7.5% RSD. Determination of trace REEs in two Gd(2)O(3) samples were performed. The method can be applied to analysis of 99.99-99.9999% high purity Gd(2)O(3). | 18,967,492 |
Determination of sulfate ion by potentiometric back-titration using sodium tetrakis (4-fluorophenyl) borate as a titrant and a titrant-sensitive electrode. | A potentiometric back-titration method for the determination of sulfate ions using a plasticized poly(vinyl chloride) membrane electrode sensitive to a titrant is described. The method is based on ion association between the excess of 2-aminoperimidinium added to the sulfate ion in the sample and sodium tetrakis (4-fluorophenyl) borate (FPB) in the titrant. The titration end-point was detected as a sharp potential change due to an increase in the concentration of the free FPB at the equivalence point. The end-point was detected even in the presence of a 20-fold excess of common cations and anions relative to the concentration of the sulfate ion within approximately 2% of titration error. A linear relationship between the concentration of the sulfate ion and the end-point volume of the titrant exists in the sulfate ion concentration range from 2x10(-4) to 3x10(-3) mol l(-1) using 10(-2) mol l(-1) FPB solutions as the titrant. The present method could be applied to determine sulfate ions in sea water. | 18,967,507 |
Raman spectroscopic determination of inosine nucleoside in nucleotides. | Raman spectroscopy has been applied to the analytical determination of inosine nucleoside in nucleotides. Spectral characteristics of aqueous solutions of lithium, potassium and magnesium salts of inosine 5'-monophosphoric acid are described. Two characteristic bands located at 1553 and 1593 cm(-1) whose frequencies are not sensitive either to the nucleotide concentration or to alkaline cations present in the medium, have been used for this purpose. The concentration ranges over which the method was applicable were 2.5-80 and 11.5-80 mg ml(-1) of inosine using the 1553 and 1593 cm(-1) bands, respectively, with relative standard deviations of 2.5 and 4.0% and detection limits of 0.25 and 1.16% (w/w). As the above bands are not generated by the standard nucleobases, this method can be applied to the quantitative determination of inosine in transfer ribonucleic acids. | 18,967,520 |
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