An investigation into the determination of stability constants of metal complexes by convolution-deconvolution cyclic voltammetry

A technique is described for calculating stability constants of metal-ligand complexes from convolution-deconvolution voltammetry. Semi-integration of the cyclic voltammetric currents with respect to time allows calculation of E(1 2 ) values in a manner comparable to the use in polarography of the Heyrovsky-Ilkovic equation. The technique described also allows determination of the ratio of the diffusion coefficients of the free and complexed metal ions and provides a second check of the stoichiometry. A reliable route to the metal-complex stability constants by the equations of Lingane and DeFord and Hume is therefore obtained. Advantages of this technique compared with the use of polarography, differential pulse polarography and pH titrations are discussed, with the complexes formed by cadmium with glycine, alanine, valine and aspartic acid as examples.     

Polarographic procedures without removal of oxygen, and other approaches to making the determinations more rapidly

One disadvantage of conventional d.c. polarography as an analytical method has always been its relative slowness. The possibility of simplifying and speeding up analyses by avoiding the necessity for removal of oxygen is demonstrated under suitable conditions with current-sampled d.c., pulse and a.c. polarography. In particular it is shown that high-frequency phase-selective a.c. polarography gives considerable discrimination against the oxygen electrode process in some aqueous media. Under these conditions, the high-frequency a.c. technique can be combined with the method of short drop-time, fast scan-rate rapid a.c. polarography to provide a most attractive method of routine analysis. Polarographic analysis in non-aqueous media without removal of oxygen is also discussed.     

The theory and practice of polarography in melts

Some of the problems of using solid micro-electrodes in molten salts are discussed. The technique of high-temperature polarography is described and some of the anomalous features of the results are examined.     

The use of DP polarography in the elucidation of organic electrode reactions

Differential pulse polarography (together differential pulse voltammetry) consists of a well-stated electroanalytical technique widely used for routine metal ion analysis. The equations obtained from rigorous treatments are difficult to handle to elucidate reaction mechanisms. In this paper the application of DP polarography to the elucidation of the mechanism of organic electrode reactions is presented. Approximate equations for a variety of electrode processes are given. Baseline subtraction and the case of ill-overlapped and close peaks are analyzed. The method is illustrated with experimental examples as the reductions of isonicotinamide and simazine at low pH values.     

Polarographic methods for measuring uncomplexed sulphide ions in natural waters

Polarography has been shown to be capable of measuring sulphide directly in untreated natural water samples. Normal pulse polarography is in good agreement with direct colorimetry and is the preferred technique. Differential pulse polarography shows that two mechanisms for the reduction of mercuric sulphide may operate. These depend on sulphide concentration and the solution equilibration time and make it difficult to accurately calibrate the signals obtained in natural waters having sulphide concentrations greater than 2×10^?6 mol l^?1. However, the shape of the peak, in any given water sample, may be used to assess the applicability of a particular calibration technique. Application of the colorimetric method to centrifuged samples suggests that labile polarographically measurable sulphide species might be loosely attached to algae.     

Mixed ligand complexes of copper with amino-acids and tartrate using differential pulse polarography. Part I

Transition Metal Chemistry - The differential pulse (d.p.) polarography technique was used to study simple and mixed ligand complexes of copper(II) with tartrate anions and amino-acids (threonine,...     

N-nitrosamines and differential pulse polarography

Differential pulse polarography is a versatile and sensitive technique which yields both qualitative and quantitative information about N-nitrosamines. The ability of the technique to carry out determinations in-situ permits the study of anchimeric, metabolic, and mechanistic properties in addition to phenomena such as kinetics and transnitrosation.     

Quick charging pulse polarography: Theory for a reversible system

The theory for quick charging pulse polarography (QCPP) is described. It has been developed to calculate, a priori, the best pulse shape in order to enhance the sensitivity, the signal to background ratio, and the scan rate of pulse polarography techniques. A general potential-time relation, independent of the pulse shape, is first deduced using the variational approach in the case of a reversible system involving two soluble species. The optimization procedure is then performed in order to cancel the undesirable charging current a short time after the pulse start. The resulting pulse shape exhibits some similitude with that of the double pulse technique but is expected to be more efficient.     

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.     

Announcements

A method for the improvement of the signal to noise ratio in differential pulse polarography is proposed. The electrode is polarized by means of a double voltage step during which the current is sampled using an integration technique in which line and random noise is cancelled.     

Polarography: A classical method with a new lease of life

Classical DC polarography was introduced by Heyrovsky in 1922. Since then substantial advances have been made in the technique, its instrumentation and methodology. These, coupled with the brilliant and innovative thinking of several workers, especially Barker, have transformed polarographic analysis into a powerful analytical tool.     

Electroanalytical behaviour of 5-nitroorotic acid

The electroanalytical behaviour of 5-nitroorotic acid has been studied at several pH values, using several techniques (DC and DP polarography and CV). The 5-nitroorotic acid undergoes five irreversible diffusion-controlled reduction waves over entire pH range considered. The optimum conditions for determination of 5-nitroorotic acid-with the above technique are also studied.     

In Process Citation

It is important to be able to determine lead in drinking water rapidly and accurately. Three polarographic methods are compared: hanging drop polarography, differential oscillographic polarography and pulse polarography. The last seems best.     

用峰鉴别技术反相高效液相色谱法测定火锅汤料中微量吗啡

本文报道了以峰鉴别技术为定性依据的测定火锅汤料中微量吗啡的反相高效液相色谱法。本法采用改良的Ｓｔａｓ－ｏｔｔｏ法分离提取复杂样品中的微量吗啡。由于采用峰鉴别技术，增加了定性参数，大大提高了定性方法的准确性。本法简便、快速。最低检出浓度为０．０４ｍｇ／Ｌ。在数十例样品分析中，与其它仪器分析结果比照，非常符合。     

Determination of complex formation constants by phase sensitive alternating current polarography: Cadmium-polymethacrylic acid and cadmium-polygalacturonic acid

The use of phase sensitive alternating current polarography (ACP) for the evaluation of complex formation constants of systems where electrodic adsorption is present has been proposed. The applicability of the technique implies the previous selection of the phase angle where contribution of capacitive current is minimized. This is made using Multivariate Curve Resolution by Alternating Least Squares (MCR-ALS) in the analysis of ACP measurements at different phase angles. The method is checked by the study of the complexation of Cd by polymethacrylic (PMA) and polygalacturonic (PGA) acids, and the optimal phase angles have been ca. −10° for Cd-PMA and ca. −15° for Cd-PGA systems. The goodness of phase sensitive ACP has been demonstrated comparing the determined complex formation constants with those obtained by reverse pulse polarography, a technique that minimizes the electrode adsorption effects on the measured currents.     

Analysis of lead titanate-zirconate ceramics: Determination of lead,titanium and niobium by differential cathode-ray polarography

Differential cathode-ray polarography is applied to the direct determination of lead, titanium and niobium in lead titanate-zirconate solid-solution ceramics containing small additions of niobium pentoxide. Titanium and niobium are determined in buffered EDTA solution at pH 4.0 and lead in 1 M hydrochloric acid. With the high precision comparative technique, relative standard deviations of 0.11% and 0.31% for lead and titanium respectively are obtained. Niobium is determined by the subtractive technique.     

Polarographic determination of hydroxylamines: application to analysis of photographic processing solutions

Procedures for the determination of hydroxylamine and N,N-diethylhydroxyIamine (DEHA), based on anodic polarographic waves, are described. The importance of using a strongly alkaline supporting electrolyte and of complete removal of dissolved oxygen is illustrated. With rapid alternating current (a.c.) polarography, 3 × 10^-6 M hydroxylamine and 4 × 10^-5 M DEHA can be detected. Detection limits with the differential pulse technique are approximately tenfold lower. In a practical application, rapid a.c. polarography is shown to be suitable for the direct determination of hydroxylamine and DEHA in photographic processing solutions. The only pretreatment of samples is dilution with a strongly alkaline supporting electrolyte. Possible interferences from other constituents of the processing solutions are avoided by using the standard addition method.     

The polished precipitate electrode: A new voltammetric method with the solid electrode

A new surface-renewal technique at the solid electrode has been developed, based on continuous polishing. Well-defined and reproducible current-voltage curves similar to those obtained in polarography are given by the "polished precipitate electrode" (PPE). The method can be used for the continuous determination of electroactive substances and for the study of electrode reaction mechanisms at the solid-liquid interface.     

Osteryoung square-wave voltammetric determination of nicarbazin in chicken tissue

Osteryoung square-wave voltammetric analysis is a rapid technique that can be used to determine nicarbazin residues in chicken tissue. The method is reproducible and can be applied to samples containing as little as 1-10 mug/g nicarbazin. This level of sensitivity is more than adequate for meeting governmental regulations. Osteryoung square-wave voltammetry is significantly faster than classical differential pulse polarography.     

Catalytic Kinetic Polarographic Determination of Trace Amount of Indium

The method of polarography for determination of trace In(III) had been reported by reference(l-2), However, The method of catalytic kinetic polarography has not been reported. Author discovered that trace indium(III) cold catalyze the discoloring oxidizing reaction of methyl orange by potassium bromate in 0.03mol/L H₂SO₄——0.25mol/L NH₃.H₂O supporting electrolyte, methyl orange exhibits a sensitive polarography wave at -0.45V(vs.SCE), The change in methyl orange concentration is traced by polarography. Hence, a new catalytic kinetic polarography method for determination of trace indium has been established. The method was used to determined trace indium in pure metallic zine with satisfactory results.