Robert Kalvoda

ADSORPTIVE STRIPPING VOLTAMMETRY IN TRACE ANALYSIS

In trace analysis the voltammetric stripping methods are popular because of their sensitivity — ranging down to sub ppb concentration. These methods are accurate and precise and the instrumentation is of low cost. The stripping methods are based on previous accumulation of the ion or compound to be determined on the working electrode. In addition to the electrolytical accumulation — used in anodic or cathodic stripping voltammetry (ASV or CSV resp.) also adsorptive accumulation of the species on the working electrode can be exploited, as many organic compounds exhibit surface active properties that are manifested by their adsorption from solution onto the surface of the solid phase.

Absorptive accumulation in stripping voltammetry

Abstract 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.

Adsorptive stripping voltammetry of electroactive organic compounds

Abstract Adsorptive stripping voltammetry at a hanging mercury drop electrode is described for various polarographically active compounds. Diazepam, nitrazepam, papaverine and aromatic nitro compounds can be determined at concentrations of 1 × 10 −9 –1 × 10 −6 M with errors of 5–7%. The effects of changing accumulation potentials and times are considered. Interference by other surface-active agents may be removed by prior molecular exclusion chromatography.

Determination of uranium by adsorptive stripping voltammetry

Abstract A voltammetric method for the determination of uranium in natural waters in the concentration range from 0.4 μg 1 −1 to 0.2 mg 1 −1 is described. The method is based on adsorptive accumulation of the uranium(VI)—pyrocatechol complex on the hanging mercury drop electrode followed by the reduction of the absorbed complex.

Polarographic analysis of solutions containing adsorbable complexes

Abstract The electrolytic reduction of some adsorbable addition complexes was followed by d.c. and a.c. polarography, single-sweep and a.c. oscillographic polarography and chronopotentiometry. The adsorption of the depolarizer leads to an increase in the sensitivity of the analytical determination with different methods to different extents ; the highest increase, almost 100-fold, was found with the controlled-current methods.

On the increase of sensitivity in oscillopolarography

In supporting electrolytes containing a mixture of sulfuric acid, ammonium thiocyanate and thiourea or urotropine the sensitivity of the oscillopolarographic determination of Cu2+, Cd2+ and Pb2+ is increased 10–50-fold. The same is found for the determination of Tl+ in acidified solutions of potassium iodide. The adsorption phenomena involved may also be utilised in stripping oscillopolarographic micro-analysis.

Adsorptive stripping tensammetry of monensin

Abstract The polyether antibiotic monensin can be detemined by tensammetry using differential pulse voltammetry at the hanging Hg electrode in the concentration range from 0.5 to 25 ppm in 0.2 M KF. In a lower concentration region (from 0.1 to 1.5 ppm), adsorptive stripping tensammetry can be used.

Oxidation of organic compounds with electrolytically generated oxidant: 1. Oxidation of methanol, ethanol and formic acid

Summary Methanol, ethanol and formic acid were oxidized in alkaline medium by means of electrolytically generated Os(VIII). From the current-time curves obtained potentiostatically, the rate constants of the oxidation of methanol (0.032), ethanol (0.22) and formic acid (0.70 mol −1 l s −1 ) in 1 M KOH at 22°C were calculated.

Oxidation of organic compounds with electrolytically generated oxidant: II. Voltammetric studies of anodic catalytic currents of ferrocyanide ions

Summary The anodic catalytic currents of ferrocyanide ions in the presence of amidopyrine, histidine, diethylaniline, etc. were studied voltammetrically and the rate constants of the oxidation of these compounds by means of ferricyanide formed at the Pt-electrode were calculated. The oxidation of amidopyrine in alkaline medium served as a model reaction. The rate constant of this oxidation is 2×103 mol−1 l s−1 in 1 M KOH at 25°C. This example of anodic catalytic currents is one of the few cases found up to date.

Cathodic stripping voltammetry of catechol and some catecholamines

Abstract The cathodic stripping voltammetry of catechol, L-dopa, dopamine and norepinephrine at a hanging mercury electrode is described. These compounds can be determined at concentrations of 2 × 10−8 to 5 × 10−7M. Interference by surface-active agents and other organic compounds was studied.