Zenon J. Karpinski

Anodic stripping voltammetry of germanium at the hanging mercury drop electrode

Abstract The Ge(IV)—Ge(0) system was investigated by cyclic and stripping voltammetry at HMDE in acidic pyrogallol medium and in phosphate, borate and carbonate buffers. It was found that germanium electrodeposited from dilute Ge(IV) solutions dissolved anodically forming two peaks corresponding to the oxidation of the unstable homogeneous and stable heterogeneous amalgams. Both peaks can be exploited analytically for the determination of traces of germanium but due to the complex nature of the germanium amalgam the sensitivity and reproducibility of the determinations are lower compared to the results obtained for metals well-soluble in mercury.

Voltammetric and chronoamperometric investigation of germanium amalgams: Part I. Properties of the homogenous amalgam

Abstract Using cyclic voltammetry and chronoamperometry with several anodic steps the deposition and particularly the oxidation of germanium from a HMDE was investigated within pH range 4–12 at Ge (IV) concentrations ranging from 4×10−7 M to 1×10−4 M in the absence of ligands capable to form the complex compounds with Ge(IV) in a solution. It was found that the initially formed product of electrodeposition is a homogeneous, usually supersaturated amalgam. Germanium from this amalgam oxidizes at about 1 V (vs. mercury sulphate reference electrode) or after some induction period, the length of which depends on concentration of Ge(0) in mercury, it begins to crystallize forming heterogenous germanium amalgam. Germanium from this heterogenous amalgam oxidizes in a separate voltammetric peak at more positive potentials. The solubility of germanium in mercury was evaluated on the basis of the oxidation current of homogenous amalgam and the value obtained is equal to (2±0.5)×10−7 M i.e. (1.1±0.3)×10−7 wt. %. Applying the Stevens and Shain method the diffusion coefficient of germanium in mercury was found to be (1.32±0.1)×10−5 cm2 s−1.

Voltammetric and chronoamperometric investigation of germanium amalgams part II. Germanium deposition from: Part II. Germanium deposition from moderately concentrated Ge(IV) solutions

Abstract Using voltammetric and chronoamperometric techniques the deposition of germanium into and onto HMDE was investigated within a pH range 6–8.5 at a Ge(IV) concentration ranging from 2×10 −5 mol l −1 to 5×10 −3 mol l −1 at scan rates from 0.002 to 20 V s −1 . The deposition of germanium from solutions with c Ge(IV) −4 mol l −1 leads initially to the formation of a homogeneous amalgam which subsequently crystallizes, forming the heterogeneous amalgam. The deposition from solution with c Ge(IV) >1×10 −3 mol l −1 leads to the appearance of the black germanium crystals on the electrode surface. The deposit obtained at high current density forms a compact, rigid layer covering the whole electrode surface. At lower deposition current densities the heterogenous germanium amalgam and germanium surface deposit are formed in parallel, and at Ge(IV) concentrations below 5×10 −4 mol l −1 the heterogenous amalgam is a main product of germanium electrodeposition.

Renewal of boundary conditions in pulse voltammetry at microdisk electrodes for non-reversible systems

Abstract Normal and reverse pulse (NP and RP) voltammetry of dopamine and epinephrine at stationary microdisk electrodes have been studied to assess the time parameters required for renewal of boundary conditions. For quasi-reversible systems, the proper choice of the initial potential in an NP experiment results in boundary renewal as for reversible systems. Experimental effects attributed to depletion were found to be close to those predicted from an equation relating the errors in the NP limiting current to ratios of pulse width to waiting time. Depletion effects observed in RP experiments were similar to those for NP experiments at the same ratio of time parameters. For irreversible systems and/or systems with follow-up chemical reactions, longer waiting times are needed for boundary renewal. Even for such systems, an adequate renewal of the surface boundary condition is assured at waiting times which are characterized by the dimensionless parameters appropriate for the experiment.

ELECTROCHEMICAL STUDIES OF FERROCENE AND FERROCENIUM ION IN ALUMINUM CHLORIDE‐N‐(1‐BUTYL)PYRIDINIUM CHLORIDE IONIC LIQUID

Der Elektronenubertragungsprozes Ferrocen/Ferrocenium-Ion wurde bei 40°C alsFunktion der Zusammensetzung der Schmelze cyclisch-voltammetrisch untersucht.

Pulse Voltammetric Determination of Thiazolidine-4-Carboxylic Acids

Abstract The electrochemical behaviour of thiazolidine-4-carboxylic acid (thioproline, Thz) and its derivatives 2-propyl-thiazolidine-4-carboxylic acid (PrThz) and 2-tetrahydroxybutyl-thiazolidine-4-carboxylic acid (AThz) has been studied by cyclic, normal and reverse pulse, differential pulse and Osteryoung square wave voltam-metrics. Anodic waves, resulting from the formation of adsorbed mercury thiazolidates, were obtained for all the compounds at mercury electrodes in acetate and phosphate buffers at pH from 3.8 to 8. the initially formed mercury compounds rapidly transform into the final products accumulating on the electrode surface. the oxidation products inhibit the anodic processes and distorted voltammetric curves were obtained at the covered electrodes. Various effects of these processes in various pulse voltammetric techniques were evident. Normal pulse voltammograms were least affected by the product transformations. Osteryoung square wave voltammetry permitted very fast determinations of Thz...

Anodic oxidation of heterogeneous germanium amalgam

Abstract The anodic oxidation of heterogeneous germanium amalgam has been studied in voltammetric and chronoamperometric experiments. Germanium crystals could be oxidized from the amalgam prepared with stirred as well as with stationary mercury cathodes. The different behaviour of these amalgams showed that only crystals close to the electrode surface participate in the anodic processes. Between −0.8 and −0.6 V the crystals are oxidized mainly through their dissolution in mercury. At less negative potentials the crystals from the surface layer are exposed and oxidized directly. The mechanisms of these processes are discussed. The main reason for crystal exposure appears to be the potential dependence of the interphase energies.

Electrochemical studies of the decomposition of thiazolidine-4-carboxylic acids in aqueous solutions

Abstract The decomposition reactions and interactions with mercury ions of thiazolidine-4-carboxylic acid (Thz) and its 2-substituted derivatives 2-propyl- (PrThz) and 2-L-arabino-tetrahydroxybutyl-thiazolidine-4-carboxylic (AThz) acids, in aqueous solutions at pH from 4.5 to 8, have been studied by cyclic voltammetry and by normal pulse and Osteryoung square wave voltammetry. Thiazolidines form unstable complexes with Hg(I) ions which transform into mercaptides. Thz and its 2-substituted derivatives decompose in nearly neutral aqueous solutions, liberating L-cysteine. The rate of the decomposition depends distinctly on the nature of the C-2 substituent and on the solution pH. It is the highest for the alkyl-substituted Thzs and exhibits a maximum at pH near 6. A significant change of the decomposition rate occurs near physiological pH. This indicates that the non-enzymatic liberation of L-cysteine in vivo may be induced by changes in pH. The correlation between the decomposition rate of Thz derivatives and literature data on their protective effect against hepatoxicity confirms that they act as prodrugs of L-cysteine. The presence of oxygen accelerates the decomposition of Thz and its derivatives distinctly.

The effect of Cu(II) ions on dopaquinone cyclization

Abstract The kinetics of the dopaquinone cyclization in the absence and presence of Cu(II) ions at pHs from 6 to 7.4 has been studied by cyclic, normal and reverse pulse voltammetry. Distinct inhibition of the dopaquinone ring closure reaction was observed in the. presence of Cu(II) ions. At pHs below 6 this effect is attributed to the formation of amino acid type complexes. At pH 7.4 the amino acid type and the catechol type Cu(II)-DOPA chelates coexist, and simultaneous interactions of copper ions with both ends of the DOPA molecule result in the association of the Cu(II)-DOPA complexes. These effects, observed at physiological pH, suggest that the rate of melanin formation is affected by the presence of Cu(II) ions.

Pulse Voltammetric Determination of Sulphur Containing Organic Compounds

Biological and medical importance of sulphur containing organic compounds (SCOC) prompted development of various methods for their determination. Several classes of SCOC, particularly containing sulfhydryl group, exhibit anodic Polarographic waves due to their reactions with mercury ions.1,2 Similar anodic behaviour has been observed recently for thiazolidine-4-carboxylic acid (thioproline, Thz) and its 2-subtituted derivatives.3 Practical applications of anodic Polarographic currents for SCOC determinations have been limited, however, due to difficulties related to autoinhibiting effects of the oxidation products accumulating on the electrode surface. Short electrolysis times of pulse voltammetric techniques may help to overcome these problems.