Differential pulse polarography and voltammetry with a microprocessor-controlled polarograph and a pressurized mercury electrode

The performance of a microprocessor-controlled polarograph with a pressurized mercury electrode system has been evaluated. For the technique of differential pulse polarography, the theory applying to the pressurized mercury electrode in the dropping mercury format is shown to be the same as for a conventional gravity-controlled mercury electrode system. At the short drop times used (0.2–0.4 s), faradaic distortion terms are shown to influence the shape of the observed differential pulse polarograms. A substantial decrease in sensitivity is also incurred in using these short drop times, compared with the longer ones generally employed in differential pulse polarography. Results for differential pulse anodic stripping conform to the usual expectations.     

The analytical performance of direct current,normal pulse and differential pulse polarography with static mercury drop electrodes

The recently developed static mercury drop electrode (SMDE) provides a fundamentally new approach to electrodes for polarography. An analytical evaluation of the electrode is presented. For a range of electrode processes, current-sampled d.c. polarography at the SMDE is useful down to at least the 10^-7 M concentration level when short drop times and fast potential scan rates are used. The improvement in the limit of detection for d.c. polarography is therefore very substantial. Improvements in sensitivity associated with normal pulse and differential pulse polarography at the SMDE compared with the dropping mercury electrode (DME) are marginal. It is concluded that at the SMDE, the analytical performance and response characteristics of d.c., normal pulse and differential pulse polarography tend to converge.     

Differential pulse polarographic determination of cyanuric chloride

Cyanuric chloride (2,4,6-trichloro-1,3,5-triazine) can be determined by fastscan differential pulse polarography in methanolic acetate buffer solution at pH 5.6 at a hanging mercury drop electrode. At positive potentials, the insoluble salt formed between cyanuric chloride and mercury(I) is adsorbed on the mercury surface and the d.p.p. current is enhanced. The detection limit is 0.2gmg ml^?1. Cyanuric chloride in air can be determined after absorption in methanol.     

The role of Fe(II) in the increased medicinal potency of curcumin analyzed by electrochemical methods

The formation of complexes of curcumin and Fe(II) was studied in aqueous media at pH 5.7 ± 0.1 by polarography, amperometry and spectrophotometry. The polarogram indicated formation of complexes between curcumin and Fe(II). Curcumin produces a well-defined direct current polarogram and differential pulse polarogram in 0.1 M ammonium tartrate (supporting electrolyte) at pH 5.7 ± 0.1. The stoichiometry of the Fe(II)-curcumin complex is 1 : 1. Anticancer studies on the drug and its metal complex have been performed against sarcoma cells (in-vitro), revealing the complex to be more potent in anticancer activity compared to the parent drug.     

Application of reverse pulse polarography to the determination of substances which form films electrochemically on the mercury electrode

The application of reverse pulse polarography to the determination of substances which form films electrochemically on the mercury electrode is illustrated with penicillamine and cysteine. The dependence of the peak current on several variables is reported and compared with theoretical predictions. It is shown that under optimal instrumental conditions (long drop times and short effective pulses) reverse pulse polarography compares favourably with both normal pulse polarography and differential pulse polarography for the determination of penicillamine and cysteine, concentrations of penicillanline as low as 5 x 10(-8)M being readily determined in the presence of copper(II).     

Polarographic currents in potassium peroxydisulphate-alkali halide systems and the determination of peroxydisulphate ion

Potassium peroxydisulphate-alkali halide systems have been studied by d.c. and a.c. (sine wave) polarography. When the mercury drop of the mercury electrode becomes covered by a film of adsorbed bromide or iodide ions, a peak due to peroxydisulphate ion is found in the a.c. polarogram at a potential more negative than that of the halide peak. This peak is probably due to a product of a chemical reaction between the peroxydisulphate ion and halide ion close to the surface of the DME. The determination of the peroxydisulphate ion by a.c. polarography is described.     

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.     

Determination of Benzoylmetronidazole in Suspension Formulations by Differential Pulse Polarography

Abstract

A rapid, reproducible and accurate method for the determination of benzoylmetronidazole in pharmaceutical suspensions is presented. Differential pulse polarography at a static mercury drop electrode is used for the reduction of the nitro group of benzoylmetronidazole.     

Removal of interference in the differential pulse polarographic determination of progestogens in some combined low-dosage oral contraceptives

Previously published differential pulse methods for the determination of certain progestogens (laevonorgestrel and norethisterone) are not applicable to combined low-dosage oral contraceptives because interference from excipients in the tablets completely eliminates the polarographic response. An ultrafiltration device allows rapid prior extraction of the interfering substances before the polarographic determination in 50% ($\text{v}\text{v}$) methanol—phosphate buffer (pH 6.0). Recoveries of 100 ± 1% were obtained by the recommended method, and data for a range of formulations are in excellent agreement with expected values. Electrode characteristics of the progestogens and interfering substances are reported, based on studies employing cyclic voltammetry at a hanging mercury drop electrode, a.c. polarography and normal pulse polarography. Competitive adsorption processes seem to occur when the progestogen and excipients are simultaneously present.     

Determination of Metronidazole in Tablet Formulations by Differential Pulse Polarography

Abstract

A method for the determination of metronidazole in pharmaceutical tablets is presented. Differential pulse polarography at a static mercury drop electrode is used to observe the reduction of the imidazole. The method is demonstrated to be simple, rapid, linear, reproducible and accurate.     

Dosage des thiols par polarographie a impulsions

The determination of thiols has been studied by pulse polarography. A single peak is obtained if the concentration is less than 10^-4 M. The electrochemical reaction involves oxidation of mercury in presence of the thiol with adsorption of the mercury thiolate on the electrode. The method is more sensitive with a negative pulse; this corresponds to reduction of the mercury thiolate formed during the drop life. The sensitivity is about 10^-7 M, i.e. 3 p.p.b. calculated as sulfur. Peak potential values are given for H₂S, nine aliphatic thiols and benzenethiol. Peak height is proportional to concentration up to about 5 · 10^-5 M. The phenomena are more complicated for concentrations higher than 10^-4 M so that the method is not then analytically useful.     

牡丹皮中丹皮酚的二阶导数差示脉冲极谱法定量研究

建立了中草药牡丹皮中丹皮酚的二阶导数差示脉冲极谱定量分析方法。丹皮酚在１ｍｍｏｌ／Ｌ－１ｍｍｏｌ／Ｌ氯化钾－水（１：１：２３）的溶液中,于－１．６．３０Ｖ（ｓ ａｇ／ＡｇＣｌ）处出现一良好的二阶导数差示脉冲极谱峰,其峰幅值与丹皮酚在０．１～０．６ｍｍｏｌ／Ｌ范围内呈非常显著的线性关系（Ｐ〈０．０１）,检测限为９．２ｍｍｏｌ／Ｌ。本法简便、快速、灵敏,且结果准确。     

Etude polarographique du rhodium(III) en milieu thiocyanate. Application au dosage microanalytique de composes organometalliques: Polarographie study of rhodium(III) in thiocyanate media. Application to the microanalysis of organometallic compounds.

Polarographie study of rhodium(III) in thiocyanate media. Application to the microanalysis of organometallic compounds.Reduction of rhodium(III) at the dropping mercury electrode is performed in thiocyanate media by classical a.c. and pulse polarography, and linear sweep voltammetry. The reduction (E$\text{1}\text{2}$ = —0.5 V vs. SCE) is shown to be a 3e irreversible transfer. Coulometric investigation confirms this result and rhodium gives a dark grey deposit at the mercury surface. This explains the i—t curves even in the presence of gelatin as maximum suppressor and the anomalous slope of log [i/(i_d - i)] at potentials more cathodic than the E$\text{1}\text{2}$ value. A.c. and differential pulse polarography are suitable for analysis down to the 0.1-ppm level. Palladium and platinum do not interfere although there is enhancement of the base line, but ruthenium affects the end of the polarogram, probably because of catalytic hydrogen evolution. Applications to organometallic compounds and industrial catalytic bimetallic grids show good agreement with the predicted compositions.     

Determination of pseudouridine at submicromolar concentrations by cathodic stripping voltammetry at a mercury electrode

Pseudouridine (5-ribosyluracil), uridine (N,1-ribosyluracil), deoxyuridine (N,1-deoxyribosyluracil) and uracil are investigated by means of d.c. polarography and by differential and normal pulse polarography. Pseudouridine, which is known to be a cancer marker, yields anodic polarographic currents in the pH range 7–11, whereas uridine and deoxyuridine are inactive under the same conditions. The polarographic response of pseudouridine obtained is due to the formation of a sparingly soluble mercury compound. Pseudouridine can be determined by differential pulse polarography in the concentration range 2–6 × 10^?6 M and by differential-pulse cathodic stripping voltammetry at concentrations two orders of magnitude lower. Small excesses of uridine, deoxyuridine or proteins do not interfere with the determination.     

An electroanalytical study of the anticancer drug dacarbazine

The electrochemical behaviour of dacarbazine [5-(3,3-dimethyl-1-triazenyl) imidazole-4-carboxamide; DTIC] was investigated by Tast and differential pulse polarography (d.p.p.) at the dropping mercury electrode, by cyclic and differential pulse voltammetry at the hanging mercury drop electrode and by anodic voltammetry at the glassy carbon electrode. Calibration graphs were obtained for 2×10^?8?2×10^?5 M DTIC by d.p.p., for 5×10^?9?1×10^?5 M by adsorptive stripping voltammetry ar a hanging mercury drop electrode, and for 1?10×10^?5 M by high-performance liquid chromatography with oxidative amperometric detection at a glassy carbon electrode. The methods are compared and applied to determine DTIC added to blood serum after a simple clean-up procedure.     

Absorptive accumulation in stripping voltammetry

A critical evaluation of adsorptive accumulation in stripping analysis, with differential pulse polarography for the measurement step, is described. Generally applicable conditions for this method are given. Adsorptive accumulation at a static mercury drop electrode is discussed for some alkaloids, local anaesthetics, surfactants and inorganic ions. Concentrations of 10^-6—10^-8 M are usually measurable.     

Determination of platinum in urine by differential pulse polarography

A method has been developed for determination of platinum in urine, after administration of cis-dichlorodiammineplatinum(II). The diethyldithiocarbamate complex of the platinum(II) is formed and extracted into chloroform, then mineralized with aqua regia. After removal of nitric acid the platinum is complexed with ethylenediamine. This chelate yields a catalytic current at a dropping mercury electrode, which is measurable by differential pulse polarography. The detection limit is ~10 ng ml . The calibration graph is linear over the range 20-800 ng ml .     

Electrochemical methods for monitoring of environmental carcinogens

The use of modern electroanalytical techniques, namely differential pulse polarography, differential pulse voltammetry on hanging mercury drop electrode or carbon paste electrode, adsorptive stripping voltammetry and high performance liquid chromatography with electrochemical detection for the determination of trace amounts of carcinogenic N-nitroso compounds, azo compounds, heterocyclic compounds, nitrated polycyclic aromatic hydrocarbons and aromatic and heterocyclic amines is discussed. Scope and limitations of these methods are described and some practical applications based on their combination with liquid-liquid or solid phase extraction are given.     

Polarographic and voltammetric determination of trace amounts of 2-nitronaphthalene

The polarographic behaviour of 2-nitronaphthalene was investigated by DC tast polarography (DCTP) and differential pulse polarography (DPP), both at a dropping mercury electrode, and differential pulse voltammetry and adsorptive stripping voltammetry, both at a hanging mercury drop electrode. Optimum conditions have been found for the determination of 2-nitronaphthalene by the given methods in the concentration ranges of 2×10^–6–1×10^–4, 2×10^–7–1×10^–4, 1×10^–8–1×10^–4 and 2×10^–9–1×10^–8 M, respectively. Practical applicability of these techniques was demonstrated by the determination of 2-nitronaphthalene in drinking and river water after its preliminary separation and preconcentration using liquid–liquid and solid-phase extraction with limits of determination of 3×10^–10 M (drinking water) and 3×10^–9 M (river water).     

Electrochemical determination of trace amounts of environmentally important dyes

A number of dyes exhibit genotoxic or ecotoxic properties leading to the need for sensitive and selective methods for their determination. Because of the easy reducibility of dyes, modern polarographic and voltammetric methods (differential pulse polarography on classical dropping mercury electrode, differential pulse voltammetry on hanging mercury drop electrode or adsorptive stripping voltammetry) are suitable for the determination of trace amounts of these substances in the general environment in the vicinity of production plants. The scope and limitations of these methods is reviewed and optimum conditions for recently developed methods are summarized. It is shown that the sensitivity of newly developed polarographic and voltammetric methods is sufficient even for the most demanding applications and their selectivity can be increased by their combination with preliminary separation using thin layer chromatography or liquid extraction.