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.     

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.     

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.     

A polarographic and spectral study of some C- and N-nitroso compounds.

A wide range of N-nitroso compounds was investigated polarographically and spectrophotometrically. In general, the =N-N0 group is reduced in a 4-electron step in acidic media, which is most suitable for differential pulse polarographic analysis at the trace level. If the groups R and/or R' attached to the nitrosamine group are saturated entities, then the resulting differential pulse polarographic peaks are broad and of little use in the resolution of mixtures. The limit of detection is of the order of 10^-6M. If R and R' are unsaturated, the polarographic peaks are much sharper, mixtures can be resolved and the limit of detection is of the order of 10^-7M, C-Nitroso and C-nitro compounds are best determined by differential pulse polarography, because the waves are comparatively large and sharp, and because the reductions occur at relatively positive potentials where co-extractible interferences from foods, etc., will interfere to a minimal degree.     

Determination of ciclazindol in biological fluids by differential pulse polarography

A differential pulse polarographic method has been developed for determination of the antidepressant, 10-(m-chlorophenyl)-2,3,4,10-tetrahydropyrimido[1,2a]indol-10-ol hydrochloride in plasma and urine. The method involves solvent extraction of the drug from the plasma or urine, evaporation to dryness and dissolution of the residue in 10% methanolic 0.01 M tetraethylammonium chloride solution followed by differential pulse polarography. The mean recovery of the drug from plasma containing 0.5–5.0 μg ml^-1 is 80%; the coefficient of variation is 5.5% at the 1.0-μg ml^-1 (2.98 × 10^-6 M) level on 2-ml samples. The method is not subject to interference from the chemical degradation products and metabolites. The techniques described have been applied to the analysis of human plasma; the polarographic and gas Chromatographic results showed good agreement.     

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.     

Polarography of disodium pentacyanonitrosylferrate(II): Part 2. Determination at Therapeutic Levels in Serum,Plasma, and Whole Blood

Disodium pentacyanonitrosylferrat(II) (sodium nitroprusside) is determined at therapeutic (ng ml^?1) levels in plasma, serum and blood with conventional and high-performance differential pulse polarography (d.p.p. and h.p.d.p.p.) at a dropping mercury electrode or a static mercury drop electrode. Serum or plasma (3 ml) is treated with perchloric acid containing 1 mg ml^?1 potassium hexacyanoferrate(II), centrifuged for 10 min and subjected to polarography. For spiked serum, calibration graphs are linear over the range 30–1000 ng ml^?1 sodium nitroprusside, regardless of the polarographic technique; the estimated detection limit is 15 ng ml^?1 (5 × 10^?8 M). Calculated therapeutic levels range from 100 to 1000 ng ml^?1. Similar results were obtained for spiked plasma. A similar procedure is suitable for whole blood and was used to study the in-vitro degradation of sodium nitroprusside (200 ng ml^?1) on incubation at 37°C. The in-vitro loss is rapid (t_{$\text{1}\text{2}$} ≈ 6 min) but meaningful in-vivo levels can be obtained when the blood is collected in a 0.9% sodium chloride solution at 0°C. Thiocyanate, the main metabolite of nitroprusside, and thiosulphate, which is a potential antidote for cyanide, do not interfere.     

Simultaneous Polarographic Determination of Lead (II) and TIN (II) by Multivariate Calibration

ABSTRACT

The polarographic waves of lead (II) and tin (II) overlap due to their similar reductive potentials and it is difficult to determine these two components simultaneously without a pre-separation. In this paper, differential pulse polarography (DPP) combined with multivariate calibration approaches, such as classical least squares (CLS), principal component regression (PCR) and partial least squares (PLS), were successfully applied to the resolution of overlapping polarographic waves of these two components in the concentration range of 0.05-3.50 mg 1^?1. Satisfactory quantitative results were obtained.     

Polarographic study of 1-methyl-5-o-chloropheyl-7- ethyl-1,2-dihydro-3H-thieno[2,3-e],[1,4]-diazepin-2-one (clotiazepam)

The electroeducation of 1-methyl-5-o-chlorphenyl-7-ethyl-1,2-dihydro-3H-thieno[2,3-e],[1,4]-diazepin-2-one (Clotiazepam) is investigated by different polarographic techniques. The electrochemical reactioninvolves a 2-electron exchange in both acidic and alkaline media. The reduction process is irreversible and the current is diffusion-controlled. With differential pulse polarography, the linear response range is 6.5 × 10^-7— 1.10 × 10^?5 M, with a relative standard deviationof 1.2% at the 2.6 × 10^?6 M level. The method is applied to the determinationof Clotiazepam in tablets after simple dissolution in 0.1 M sulphuric acid.     

Anodic behaviour of 2-mercaptoethanol at a mercury electrode

The anodic processes which occur at the mercury electrode in 2-mercaptoethanol solutions are studied by various polarographic techniques (d.c., a.c. and differential pulse), controlled-potential coulometry, cyclic voltammetry and differential capacity curves. Two steps are distinguished in the process: a one-electron charge transfer and a dismutation step leading to the formation of a mercury(II) mercaptide. The final product is isolated and analyzed. Differential-pulse polarography can be used to determine ?10^?4 M 2-mercaptoethanol with a limit of M.     

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.     

Comparison of differential pulse and alternating current polarography in the soft-modelling study of the complexation of Cd(II) by the fragment Cys-Gly and by the phytochelatin (γ-Glu-Cys)<Subscript>2</Subscript>Gly

A comparison of a differential pulse polarographic with a phase sensitive alternating current polarographic study of the Cd-Cys-Gly and Cd-PC₂ systems [PC₂ being a phytochelatin of general structure (γ-Glu-Cys) _n -Gly, with n = 2] has been performed. The chemometric multivariate curve resolution method with alternating least squares was applied in the experimental data analysis. The results obtained by both polarographic techniques have made it possible to find out the formation sequences of the complexes and their final stoichiometries. The alternating current polarograms compared with the differential pulse ones show some differences (a new signal and an important shift of peak potentials), which anyway are consistent with some of the conclusions obtained by differential pulse polarography. This fact implies that although the alternating current polarography results need some corrections before data treatment, they provide extra information that complements the conclusions achieved by differential pulse polarography. Figure Voltammograms at ACP(−10°), ACP(−65°) and corrected ACP during the titration of a 10⁻⁵ mol L⁻¹ Cd(II) solution with PC₂ at pH 8.5 in 0.05 L⁻¹ Tris.     

Electrochemical behavior and voltammetric determination of the herbicide metribuzin at mercury electrodes

The electrochemical behavior of the herbicide metribuzin (4-amino-6-tert-butyl-4,5-dihydro-3-methylthio-1,2,4-triazin-5-one) at mercury electrodes was studied in aqueous solutions by direct current (DC) and tast polarography, differential pulse (DPV) and cyclic voltammetry (CV), and controlled-potential coulometry. The electrolysis products were separated and identified by chromatographic techniques combined with mass spectrometric detection. The reduction process in acid media includes two irreversible steps. In the first four-electron step the N–NH₂ and the 1,6-azomethine bonds are reduced. The second step leads to the formation of 5-tert-butyl-2,3,4,5-tetrahydroimidazol-4-one at the mercury-pool electrode. The first reduction step combined with adsorptive accumulation of the herbicide molecule at the mercury electrode surface was used for its determination by differential pulse adsorptive stripping voltammetry (DPAdSV). Calibration curves were linear in the range 1–30 μg L^–1 with a detection limit of 0.27 μg L^–1 (1 nmol L^–1) under the conditions used (buffer pH 4.5, E_acc = –0.45 V relative to Ag/AgCl and t_acc = 10 s). Preconcentration on solid-phase extraction columns (SPE-phenyl) was used for the determination of very small amounts of metribuzin in river water samples. Recovery was approximately 97%. The reproducibility of the analytical procedure including SPE treatment and DPV determination was expressed as relative standard deviations of 2.53 and 3.66% for 2 and 6 μg L^–1 metribuzin, respectively.     

Electrochemical study and polarographic determination of ranitidine

In the polarographic reduction of ranitidine, an H₂-antagonist of histamine, three waves are observed; their half-wave potentials and limiting currents depend strongly on the pH of the solution. The first and second waves are due to reduction of teh protonated, CHNO₂H⁺, and unprotonated, CHNO₂, nitroethene group of ranitidine, respectively; the origin of the third wave is unknown. The characteristics of the second and third waves are studied in acetic acid/acetate buffer at pH 5.5; the first wave does not appear at this pH. The second wave (E_{$\text{1}\text{2}$} = ?0.90 V, vs. Ag/AgCl) is useful for determining ranitidine in the range 2.4–4.9 × 10^?4 M by direct current polarography and in the range 2.5 × 10^?7?2.05 × 10^?5 M by differential pulse polarography.     

The specific fluorimetric determination of digoxin.

The simultaneous determination of Cd, Cu, Pb and Zn in lead and zinc concentrates by fundamental, second-harmonic and linear-sweep a.c. and pulse polarographic methods is described. Calibration curves are linear over wide concentration ranges, so that both major and minor trace constituents can be determined in the same experiment; thus the polarographic method is highly competitive with atomic absorption spectrometry (a.a.s.). Conventional a.c. polarography and a.a.s. were compared in the first instance with conservative instrumentation. More sophisticated polarographic methods were then utilized; with the phase-selective linear sweep a.c. (fundamental- and second-harmonic) methods the four elements were determined simultaneously from voltammograms obtained in less than 20 s down to the 10^-6-10^-7M concentration range.     

The solvent extraction of flurazepam and its major metaboutes and their determination by polarography

The solvent extraction of flurazepam and its major metabolites from aqueous solutions of varying pH has been studied at concentrations encountered in body fluids following therapeutic dosage. Distribution ratios have been calculated over the pH range 0–14 and for the solvents, ethyl acetate, diethyl ether, cyclohexane and petroleum ether (40–60°C). Based on this study, a solvent extraction scheme is evaluated for the recovery of such concentrations of these compounds in mixtures, with final polarographic determinations. Recoveries exceeding 95% were found; the method is specific for the determination of flurazepam and its acetic acid metabolite in mixtures. The total concentration of the remaining metabolites, i.e. the hydroxyethyl-, N-1-desalkyl-, and N-1-desalkyl-3-hydroxy metabolites can be estimated after solvent extraction and differential pulse polarography in alkaline solutions.     

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.     

Determination of cyanuric acid in swimming pool water by differential pulse polarography

A reliable differential pulse polarographic method is described for the determination of cyanuric acid (1,3,5-triazine-2,4,6-triol) in pool water. Cyanuric acid in the range 10^?5–10^?3 M is determined by means of the peak at ca. –60 mV (vs. Ag/AgCl/3 M NAcl). The high sensitivity of the polarographic technique allows ten-fold dilution of samples, thus avoiding matrix effects. It it shown that the peak can be attributed to formation of insoluble mercury(I) cyanurate, Hg₂(HC₃N₃O₃), at the mercury electrode.     

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 study and analytical applications for new biologically active 2-nitrophenylbenzimidazole derivatives

The present study addresses the electrochemical behavior and the analytical applications of six 2-nitrophenylbenzimidazole derivatives with activity against Trypanosoma cruzi. When studied in a wide range of pH, by differential pulse polarography, tast polarography and cyclic voltammetry, these compounds exhibited two irreversible cathodic responses. With analytical purposes, the differential pulse polarography mode was selected, which exhibited adequate analytical parameters of repeatability, reproducibility and selectivity. The percentage of recovery was in all cases over 99%, and the detection and quantitation limits were at the level of 1 × 10⁻⁷ mol L⁻¹ and 1 × 10⁻⁶ mol L⁻¹, respectively. In addition, the differential pulse polarography method was successfully applied to study the hydrolytic degradation kinetic of one of the tested compounds. Activation energy, kinetic rate constants at different temperatures and half-life values of such application are reported.