Microdetermination of benzoylhydrazine and some methoxylated derivatives by using differential pulse polarography

The differential pulse polarographic behaviour of benzoylhydrazine, m-methoxy benzoyl-hydrazine, and o-methoxy benzoylhydrazine has been investigated in Britton-Robinson buffer. The peaks obtained at pH 5 are recommended for the microdetermination of these compounds. The benzoylhydrazine can be obtained with high degrees of accuracy with an experimental detection limit of 4 × 10⁻⁶ M in simple aqueous and aqueous ethanol mixtures.     

Differential pulse polarographic behaviors of p-nitrosodimethylaniline: Application for microdetermination of NADH

The differential pulse polarographic behavior of p-nitrosodimethylaniline has been investigated in Britton-Robinson buffer and phosphate buffer. The peak obtained at pH 8.0 is recommended for the trace determination of this compound, with an experimental detection limit of 18 ppb (1.2 × 10^?7M) in simple aqueous solution. The method is also applied for the indirect microdetermination of NADH. The experimental detection limit of NADH is shown to be 1.05 × 10^?6M.     

Differential pulse polarographic determination of some organotin(IV) compounds in dimethyl sulfoxide

The differential pulse polarographic behavior of two series of organotin(IV) compounds having the general formula R_xSnCl_{4 − x} (R = Me, Ph; x = 1, 2, 3, 4) has been investigated in DMSO. The peaks obtained are recommended for the trace determination of these compounds. Linear calibration curves are obtained over the concentration range 10⁻⁴ –10⁻⁶ M.     

The determination of phenobarbital and diphenylhydantoin in blood by differential pulse polarography

A sensitive differential pulse polarographic assay was developed for the determination of phenobarbital or diphenylhydantoin in blood. The assay involves the selective extraction of the compound into chloroform from whole blood buffered to pH 7.0. After suitable “clean-up” of the sample, each compound is nitrated in 10% potassium nitrate in sulfuric acid at 25° for 1 h. The nitro-derivatives are extracted into ethyl acetate, and the residues are dissolved in 1 M phosphate buffer (pH 7.0) or 0.1 M sodium hydroxide for phenobarbital and diphenylhydantoin, respectively; the solutions are deoxygenated, and analyzed by differential pulse polarography. The overall recovery of phenobarbital and diphenylhydantoin from blood was 72.3% ±6.5 (s_r) and 76.7 ±2.3 (s_r) respectively. The sensitivity limit is 1–2 μg ml^-1 of blood for both compounds. A modified assay for the determination of both compounds in blood with t.l.c. separation was also developed.     

Simultaneous determination of the isomers of nitrophthalic acid by differential pulse polarography

A differential pulse polarographic method has been developed for simulataneous determination of isomers of nitrophthalic acid. In ammonia buffer (1.0 M), the peak potentials for the reduction of 4-and 3-nitrophthalic acids are ?0.54 and 0.67 V vs. SCE, respectively. Response of peak current vs. concentration of each isomer is linear over three orders of magnitude change in concentration. The detection limit for both 4-and 3-nitrophthalic acid is 0.2 mg l^?1. A typical sample can be analyzed for both isomers of nitrophthalic acid in less than 15 min.     

Differential pulse polarography as a tool for the determination of trace levels of nicotinamide adenine dinucleotide (NAD+) and nicotinamide adenine dinucleotide phosphate (NADP+) in aqueous solution

The differential pulse polarographic behavior of NAD⁺ and NADP⁺ has been investigated in phosphate buffer. The peaks obtained at pH 8.0 are recommended for the trace determination of these compounds. Linear calibration curves are obtained over the concentration ranges from 2.6 × 10⁻⁷ to 2.6 × 10⁻⁵M for NAD⁺ and from 2 × 10⁻⁶ to 4 × 10⁻⁵ for NADP⁺.     

Electroreduction and pulse-polarographic determination of nicotinamide in multivitamin tablets

The electroreduction of nicotinamide has been investigated by d.c., a.c. and pulse polarography, cyclic voltammetry and coulometry. A single well-defined polarographic wave is obtained from 2 M sulphuric acid and from 0.1 M sodium hydroxide. In both media, nicotinamide undergoes an irreversible 2-electron reduction; 3 hydrogen ions are consumed in acidic medium and two hydrogen ions in alkaline medium. The current is diffusion-controlled and proportional to the concentration in the range 0.6–120 μg ml^?1. Reduction mechanisms are proposed. A simple and rapid method for the determination of nicotinamide in multivitamin tablets by differential pulse polarography is described.     

Differential Pulse Polarographic Determination of Nitrate in AUT Solution

A differential pulse polarographic method for the determination of nitrate ion has been developed. With 0.5 M CaCl₂ as supporting electrolyte, NO^?₃ is reduced to give a peak with E_1/2=–1.836 Volt vs. the Ag/AgCl electrode. The differential pulse polarographic peak height is proportional to the nitrate concentration from 20 to 60 ppm. The detection limit for nitrate is 2 ppm in pure aqueous solution. In the determination of 40 ppm nitrate a relative precision (relative standard deviation) of less than 2% was achieved. Nitrite interferes seriously and should be absent if accurate results are required. The method has been applied to the determination of nitrate in Ammonium Uranyl Tricarbonate (AUT) Solution, results obtained by this method are compared to those obtained by ion chromatography. The agreement between the two sets of results suggests that the DPP method can be used with a fair degree of confidence.     

Determination of subnanomolar concentrations of tungsten (VI) by catalytic adsorption polarography

A new differential pulse polarographic method for the determination of W(VI) using a catalytic adsorption wave is described. W(VI) is first chelated by 7-iodo-8-hydroxyquinoline-5-sulfonic acid at pH 0.5. The complex ion formed is strongly adsorbed on the surface of a dropping mercury electrode. At a potential of –0.95 V versus the Ag/AgCl (3M KCl) reference electrode the adsorbed complex is reduced by the polarographic current and oxidized very fast by hydrated hydrogen ions providing the oxidized form of the complex ion for repeated redox cycles. As the redox process taking place in the electric double layer, the diffusion of the complex does not limit the polarographic current. Therefore, high currents occur, and consequently, a very high sensitivity is obtained. The practical detection limit (PDL) is 3.7 ng W/kg solution corresponding to 2 × 10^–11 M. The standard deviation of single values is 1.2 ng/kg at the concentration of 91 ng/kg lying in the middle of the linear part of the calibration curve. Because Mo (VI) gives a very similar catalytic adsorption wave, serious mutual interferences occur in the analysis of mixtures of both species. An effective separation of Mo(VI) was worked out. Using 1% (w/v) solution of trioctylphosphinoxide in kerosene, Mo(VI) can almost completely be extracted from 1.8M HCl with a threefold extraction resulting in a separation factor of 40000.     

Voltammetric determination of agriculturally-significant benzenearsonic acids

Direct current and differential pulse polarographic measurements are reported on a series of substituted benzenearsonic acid compounds that are important in agricultural applications. Compounds studied were o-aminobenzenearsonic acid, p-aminobenzene-arsonic acid, p-nitrobenzenearsonic acid, p-ureidobenzenearsonic acid, and 3-nitro-4-hydroxybenzenearsonic acid. Polarographic reduction potentials varied with pH for all compounds, shifting to more negative values as the pH was increased. Although diffusion-controlled reduction waves were observed in all cases, some compounds exhibited a dependence of E$\text{1}\text{2}$ on concentration, especially at relatively high concentrations. Differential pulse polarographic peak currents were proportional to concentration from 10^-4 M to 10^-6 M.     

Electrochemical reduction behaviour of the synthetic pyrethroid insecticide cyfluthrin and its determination in formulations and environmental samples

The polarographic behaviour of cyfluthrin (CY), an α-cynoester pyrethroid, was studied using a dropping mercury electrode and hanging mercury drop electrode in methanolic Britton–Robinson (B–R) buffer of pH 2.0–12.0 with different ionic media. The nature of the electrode process was examined, the number of electrons was evaluated, and the reduction mechanism was proposed. Quantitative determination was achieved in the concentration range of 6.0?×?10^?8 to 1.15?×?10^?5?mol?dm^?3 using a differential pulse polarographic method with a lower detection limit of 2.4?×?10^?8?mol?dm^?3. The proposed method was successfully applied in the determination of CY in formulations, grains, soils, and spiked water samples.     

Polarographic Determination of Aztreonam

Abstract

The polarographic behaviour of Aztreonam is studied. In acid media, at pH values lower than 6, in differential pulse polarography a peak is observed at a potential close to ? 0.6 volts. The optimum conditions for the polarographic signal are established and the different parameters affecting the electrochemical process are studied. The relationship between peak intensity and the concentration of Aztreonam is linear for concentrations lower than 1.0 ? 10^?5 M, the detection limit being 1.4 × 10^?8 M It was observed that the presence of 1-arginine does not affect the polarographic signal of Aztreonam to any significant extent.     

Electrochemical determination of N,N-dimethyl-4-amino-4′-aminoazobenzene

N,N-Dimethyl-4-amino-4′-aminoazobenzene has been determined using differential pulse polarography. Fast-scan modification and linear-scan voltammetry at a hanging mercury drop electrode was used with a detection limit of less than 10⁻⁸ mol liter⁻¹. Differential pulse polarography was then used to analyze mixtures of the above depolarizer with azobenzene and N,N-dimethyl-4-aminoazobenzene, either directly, or after a TLC separation.     

Simultaneous polarographic analysis of pyrazine and its methyl derivatives by iterative target transformation factor analysis

The polarographic waves of pyrazine and its methyl derivatives are seriously overlapping, so they cannot be determined individually by polarographic methods without a prior separation. In this paper, a chemometric approach, iterative target transformation factor analysis (ITTFA), is developed and applied to the determination of mixtures of pyrazines at trace level (2.0–9.0 × 10⁻⁶moll⁻¹) by using differential pulse polarography (DPP) and a static mercury drop electrode (SMDE). Different from the general ITTFA method, only one-dimensional measurement data of n − 1 standards and an unknown were used in this work. It produced acceptable results with average recoveries in the 96–108% range and relative standard errors in the 3.4–9.5% range.     

A polarographic study of some N-oxygenated products of N-ethyl-β-methoxy-β-(3'-trifluoromethylphenyl)-ethylamine (sk and f 40652a)

The polarographic behaviour of N-hydroxy-β-methoxy-β-(3'-trifluoromethylpbenyl)-ethylamine, N-ethyl-N-hydroxy-β-methoxy-β-(3'-trifluoromethylphenyl)ethylamine and (3-methoxy-β-(3'-trifluoromethylphenyl)acetaldoxime has been studied over the pH range 0—14. The hydroxylamines gave rise to anodic and cathodic behaviour whereas the oxime gave only a cathodic wave. The mechanism of the oxidation and reduction processes was investigated by d.c. polarography and preparative micro-coulometry. The optimum pH values for analytical purposes were 7, 8 and 4 for the two hydroxylamines and the oxime, respectively. The polarographic behaviour of a mixture of the three compounds was studied and the determination of traces of such compounds by differential pulse polarography is discussed.     

Use of a data treatment software for the resolution of overlapping differential pulse polarographic peaks

Summary A procedure based on the use of the Beckman Data Leader Software is proposed for resolving binary mixtures of electroactive analytes when their differential pulse polarographic peaks are overlapping without any separation step. The resolution is made by measuring in the selected zero-crossings of the first derivative differential pulse polarograms. For testing the procedure, two well-known systems were used, cadmium (II)-indium (III) and thallium (I)-lead (II) mixtures. The four metallic ions can be determined in diverse ratios with quantification limits lower than 10^–7 mol/l.     

Polarographic determination of thiabendazole

Summary Polarographic Determination of Thiabendazole Thiabendazole is used as a fungistat on citrus fruit to protect it from decay.In order to work out a polarographic determination the electrochemical behaviour of thiabendazole was investigated by sampledd c polarography and differential pulse polarography. Thiabendazole shows one wave or peak in the polarogram, when a short drop time (0.4 s) is used. Detection is most sensitive at pH 8. The current measured is proportional to the concentration. The detection limit is 0.5 ppm.By evaluating further experimental data it was possible to conclude, that mercury is first oxidised. Thereby two electrons are exchanged. Then mercury(II) ions formed in this way react with two molecules thiabendazole. Two protons are involved in this chemical process.Applying drop times greater than 0.4 s and concentrations higher than 1.5·10^–4 M a polarogram with two peaks is formed. This is due to the adsorption of the reaction product.For quantitative determination several citrus fruits were peeled and the peels were extracted with ethylacetate. After removing interfering substances by shaking with sodium hydroxide solution, thiabendazole was extracted by diluted hydrochloric acid and quantitatively determined by differential pulse polarography. The recovery of thiabendazole is 70.0% with a relative standard deviation of 2.9%. For all samples investigated the thiabendazole concentrations were below the permitted value.Cordially dedicated to Univ.-Prof. Dr. Dr. h. c. K. Kratzl on the occasion of his 70th birthday.     

Nitration et dosage de la phénylalanine

This paper comprises a study of the conditions for nitrating phenylalanine and an investigation of the compounds obtained, polarographic and chromatographic methods being employed. At the same time some nitrobenzoic acids that are found among the nitration products of nitrophenylalanine were examined by both these methods.A method has been proposed for the polarographic determination of phenylalanine, by means of which as little as 30γ of this substance can be detected in 10 ml solution. With concentrations between 2.4.10^-4M and 6.10^-3Mt, the error is less than 2.5%, with those of the order of 2.10^-5M it approaches 12%.     

Differential pulse polarographic behaviour of thiazopyr herbicide and application to its determination in fruit juice and soil samples

A differential pulse polarographic method for the determination of the herbicide thiazopyr has been developed. The polarographic study of thiazopyr exhibited two well-defined cathodic peaks within the pH range of 1.0 to 8.0. The variation of pH and polarographic parameters indicated that the optimum conditions under which thiazopyr could be reduced were a pH 7.0 BR buffer solution, a reduction peak potential of ?1270 mV (vs. SCE), scan rate of 5 mV s^?1, pulse amplitude of 50 mV with pulse duration of 50 ms at an ambient temperature of 25 ± 3°C. The main reduction peak was characterised by cyclic voltammetry as being irreversible and diffusion-controlled. A linear relationship between the peak current and the concentration of thiazopyr was obtained in the range of 0.43–38.6 µg mL^?1, with a detection limit of 0.127 µg mL^?1. The proposed method was successfully applied to the determination of thiazopyr in spiked fruit juice and soil samples. The mean recoveries of the 19.8 µg g^?1 and 3.96 µg mL^?1 thiazopyr spiked to soil and orange juice were 20.2 ± 1.0 µg g^?1 and 3.84 ± 0.12 µg mL^?1, at 95% confidence level, respectively. The sufficiently good recoveries and low relative standard deviation (RSD) data confirm the high accuracy and precision of the proposed method. The interferences effects of several commonly used pesticides and inorganic species were also studied. Interfering effects were eliminated either by providing selectivity with pH, or using EDTA as complexing agent.     

A microcomputer-based data acquisition and processing system for electrochemical analysis

The system described for electrochemical analysis includes ensemble averaging, boxcar integration and background subtraction. A digital storage oscilloscope interfaced to a microcomputer provides these data-processing techniques for the differential pulse polarographic determination of molybdenum. The system is easily interfaced to the polarograph. An approximately four-fold improvement in the detection limit for molybdenum — to 2.7 × 10^-4 ppm — was achieved by using a combination of ensemble averaging and background subtraction.