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.     

Contribution to the study of pulse polarography part II. Digital simulation of ce mechanisms in normal pulse polarography

Several CE electrode processes have been introduced in a digital simulator of normal pulse polarography with widely varying values of the homogeneous and heterogeneous kinetic parameters. The effects on the shape of the normal pulse polarograms are described.     

Adsorbing colloid flotation separation and polarographic determination of Mo(VI) in water

A method is described for the flotation and determination of Mo(VI) in water at ng/ml levels. Mo(VI) is preconcentrated and separated by adsorbing colloid flotation employing aluminium(III) hydroxide as collector and sodium lauryl sulphate as surfactant at pH 5.3 ± 0.1. The molybdenum content in the froth is estimated by using the catalytic wave of Mo(VI) in the presence of nitrate by charging current compensated d.c. polarography (CCCDCP) or differential pulse polarography (DPP). The effect of variables such as pH, ionic strength, concentration of collector and surfactant, time of stirring and gas flow-rate on the recovery of Mo by flotation is reported. The effects of various cations and anions on the flotation and determination of Mo are studied. This method is employed for the determination of molybdenum in natural fresh water samples.     

Polarographie Impulsionnelle Differentielle de Derives Triiodes De L'acide Benzoique

Abstract

Three triiodo derivatives of benzoic acid have been separated and analyzed by differential pulse polarography in acidic, neutral and alkaline medium. The selectivity of the method, and a comparison of the resolution with conventional polarography, are pointed out. An order of reduction of the atoms is proposed.     

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.     

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.     

High-performance pulse and differential pulse polarography: Part I. Theoretical considerations

A theoretical approach is given for complete elimination of the charging current caused by drop growth in modified normal and differential pulse polarography (n.p.p. and d.p.p.). Maximum sensitivity can be obtained in modified n.p.p., but the resolution of waves is better in modified d.p.p. or can be increased in differential modified n.p.p. The best overall performance can be achieved with modified d.p.p., considering sensitivity and wave resolution together. Preliminary results for the determination of chloramphenicol are described.     

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).     

Pulse polarograpmc study of the electrochemical reduction of lucigenin in aqueous medium

The electrochemical reduction of lucigenin (bis-N-methylacridinium nitrate) in aqueous solution was studied by normal pulse polarography, normal pulse polarography with differential detection of the current, and differential pulse polarography with cathodic and anodic pulses at several pulse amplitudes. The effects of pH and lucigenin concentration were studied. In confirmation of an earlier d.c. polarographic study, lucigenin is shown to be reduced in two separate one-electron steps. An adsorption peak accompanies the first step, while the second, below pH 3.5, is catalytic owing to chemical regeneration of the intermediate reduction product at the electrode surface.     

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.     

Use of computerized instrumentation for pseudo-derivative direct current and normal pulse polarography with correction for charging current

The application of computerized instrumentation to pseudo-derivative d.c. and normal pulse polarography is described. Calculation of background current by means of a linear least-squares fit of data obtained prior to the rising part of the sigmoidal d.c. or pulse curve and extrapolation to other potentials enables close to the faradaic response to be obtained over wide concentration ranges. After subtraction of background current, least-squares fitting of the sigmoidal curve enables data smoothing to be undertaken and other calculations to be performed. Pseudo-derivative curves obtained by plotting current differences obtained from corrected and smoothed data provides limits of detection comparable to those of more sophisticated polarographic methods. The reduction of cadmium in 1 M NaCl is considered because it occurs at potentials near the electrocapillary maximum where charging current correction is most difficult. The limits of detection are 10^-7 M for the pseudo-derivative d.c. method, and 10^-3 M for the pulse method.     

Voltammetric study of some macromolecule - metal complexes

The usefulness of a voltammetric model for studying macromolecule - metal complex systems is verified. Complexes formed by a metal ion (Zn(II), Cd(II), Pb(II) or Cu(II)) and a macromolecule (polymethacrylic (PMA), polyacrylic (PAA), alginic (AA) or polygalacturonic (PGA) acids) are investigated. Several voltammetric techniques have been used: sampled direct current polarography (DCP), normal pulse polarography (NPP), differential pulse polarography (DPP), reverse pulse polarography (RPP), cyclic voltammetry (CV) and differential pulse anodic stripping voltammetry (DPASV). Results confirm the validity of the model, in determining not only formation constants but also diffusion coefficients of the complexes. The behaviour of some systems agrees with that predicted by the model. Nonetheless, other systems only partially fulfil the predictions for different reasons, which are discussed.     

Chronocoulometry of tris-2,2′-bipyridine cobalt(II) and related transition metal complexes

Integrated pulse polarography and similar techniques have been used for study of reduction of bipyridine complexes of Co(II), Ni(II) and partially also Fe(II) in aqueous solutions. By proper choice of pulse and detection intervals, it is possible to confirm or separate the contribution of reactant adsorption. The pulse polarography of the product reoxidation shows a finite charge transfer rate in the case of tris-2,2′-bipyridine cobalt complex.     

Polarographic Study of Lead-Tropolone Complexation

Abstract

A.C., D. C. and derivative pulse polarography of lead-tropolone complexes has been studied. It has been shown that the application of usual treatments for complexation in d. c. polarography are invalid in this system, where the irreversible wave in presence of the ligand is a composite step. It seems generally advisable to apply derivative pulse or a.c. polarography before using non-reversible d.c. steps for evaluation of K and p.     

Reactant adsorption in analytical pulse polarography: An outline in terms of the concentration profile

The consequences of adsorption of the electroactive species in analytical pulse polarography are discussed. For both normal pulse polarography (NPP) and differential pulse polarography (DPP) explanations are given in terms of the concentration profiles as they are developed upon adsorption before pulse application. An approximate interpretation of the depressed NPP limiting current is sometimes possible by taking its dependence on pulse duration into account. In a number of cases NPP offers the possibility of avoiding adsorption effects by choosing a suitable initial potential. In DPP reactant adsorption generally causes peak enlargement, but the theoretical approach is complex and practical means for checking or eliminating adsorption effects in DPP are limited. Analytical calibration curves start with a linear portion corresponding with the linear adsorption regime; at higher concentrations the DPP curve bends downwards, whereas the NPP curve bends slightly upwards, before reaching the linear region of diffusion control. Several analytical pitfalls connected with the adsorption phenomena are indicated.     

Pulse-polarographic analysis of nucleic acids and proteins

Nucleic acids and proteins were studied by means of derivative and normal pulse polarography, and d.c. and a.c. polarography in connection with the dropping mercury electrode. It was shown that natural ribonucleic acids, as transfer, ribosomal and viral RNAs yield derivative pulse-polarographic peaks; from their heights and potentials conclusions can be made about their content of ordered structure in solution, similarly as in the case of deoxyribonucleic acids studied earlier. Synthetic single-stranded polyribo-cytidylic acid yields a well developed peak, whereas in the double-helical complex with polyriboguanylie acid it is inactive when using either derivative pulse polarography or d.c. polarography. Well developed peaks were obtained also with albumin (a protein containing reducible?S?S? groups), while only an inflex was observed on the d.c. polarogram. Proteins were also studied in media containing cobalt (Brdi?ka's solution) or nickel and it was shown that derivative pulse polarography due to its high sensitivity and accuracy enables us to carry out the measurements even in less common media than Brdi?ka's solution. This fact could be exploited in clinical chemistry as well as in the investigation of the nature of catalytic currents of proteins. The currents of double-helical polynucleotides obtained by means of normal pulse polarography exhibit a marked dependence on the initial potential and cannot represent a reliable indicator of structural changes of biopolymers in solution. They can however, be used in studies of the influence of the polynucleotide adsorption at different potentials on the subsequent reduction.     

Methods of realisation of short rise-times of the cell voltage in pulse polarography

Three methods for producing a voltage step on the dropping mercury electrode cell, as required in pulse polarography, are considered: the double pulse shape of the potentiostat reference voltage, iR-compensation, and charge injection. On an analogue model two methods of iR-compensation are simulated and compared, with reference to their convenience for reducing the rise-time of the polarizing voltage. A charge injection technique is proposed in which the potentiostat reference voltage is derived from the cell voltage after charge injection by taking a sample of it and applying it to the reference input of the potentiostat.     

正交回归多元标准加入法同时测定干扰组分

提供了同时测定混合物中彼此严重干扰的多种组分的新方法。该方法采用多元标准加入法的正交回归设计,因此,由微机上的正交回归分析,得到一组准确的回归方程,该方法用于光度法中,同时测定了工业污水中的铜,镍,镉,锌,并用于差分脉冲极谱法中,同时测定了河水中的铅,铊,镉,测定结果的误差均不大于4％,这个结果说明该方法具有良好的准确性和可靠性。     

Contribution a l'électrochimie des thiols et disulfures : Partie I. Cystéine et cystine

A study of the electrochemical characteristics of cysteine and cystine was carried out by d.c., a.c. and differential pulse polarography. Up to three waves were observed depending on the concentration and pH. The waves of the two amino acids could be separated in a borate buffer of pH 9.2. Differential pulse polarography made it possible to determine as little 0.12 mg of cysteine and 0.24 mg of cystine per litre.     

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.