Search results for "Polar"

Electrochemical study of intramolecular charge transfer complexes derived from 1,4-naphthoquinone Part 1. Electroreduction

1995

Abstract Electrochemical investigations (polarography, cyclic voltammetry, rotating ring-disk electrode voltammetry) of intramolecular charge transfer complexes (AC) derived from 1,4-naphthoquinone were performed in acetonitrile. It is concluded that in the first one-electron stage of its electrochemical reduction the AC is in a complexed form. At the same time the amino moiety, which shows a marked inductive (−I) effect, acts as an electron donor in the donor-acceptor (D-A) interaction. Facilitation of the reduction of the quinone part by the aryl amine residue is compensated by the D-A interaction, which makes the electroreduction more difficult. By using ultramicroelectrodes it was shown…

Ascorbic Acid Stability in Ground Asparagus Samples and in Oxalic Acid Extracts

1995

To establish the storage conditions for asparagus preparation before ascorbic acid determination, samples were ground, the mass was divided into three aliquots that were, respectively, stored at 4°C, – 18°C, or extracted with 1% oxalic acid. The extract was further split into aliquots and stored at 25°, 4°, –18° and -75°C. Ascorbic acid content was measured at different times of storage by a polarographic method. The rate of degradation increased with storage temperature; the degradation rate was higher in ground samples than in extracts; no significant changes in ascorbic acid content were observed in extracts stored for 7 days at -18° or for 90 days at -75°C.

Constant-potential electrolysis: determination of diffusion coefficients of thallium by using a hanging mercury drop electrode.

1976

The technique of constant-potential electrolysis at a stationary spherical electrode (hanging mercury drop) was investigated for the determination of the diffusion coefficient of Tl(I) in sodium citrate-sodium hydroxide medium and of Tl in mercury. Current-time curves, at controlled potential, were obtained, covering periods from 1 to 25 sec after the start of the electrolysis. The influence of applied potential, time of electrolysis, convection and shielding of the electrode was studied.

Polarographic determination of glycine with a dropping copper amalgam electrode

1975

The anodic oxidation of a dropping copper amalgam electrode in presence of dilute solutions of glycine in 0.50 M NaClO4 has been studied. An anodic wave at −0.28V (SCE) is observed, yielded by diffusion of glycinate anion in the solution towards the electrode surface. The wave-heights increase with the glycinate concentration (function of glycine concentration and pH value) until the anodic oxidation is controlled by the metal diffusion into mercury. The effect of pH is interpreted by attributing it to the depolarizer effects at glycinate anion even though the zwitterion is present in much larger concentrations. The applicability of anodic oxidation of a dropping copper amalgam electrode in…

Interactions of N-heteroalkylaminomethylenebisphosphonic acids with Cd(II) ions: Electrochemical and spectroscopic investigations

2015

The aminomethylenebisphosphonates are known to be excellent chelators for many metal ions. In this work, the coordination properties of three different aminomethylenebisphosphonates with N-substituted heteroalkyl moieties (L1, L2 and L3) and their N-pyridyl derivative (L4) toward cadmium(II) ions are described. Due to their coordination abilities over a broad range of pH, the compounds of this group are good candidates for heavy metal detoxification. To determine the stability constants and the coordination mode of formed aminomethylenebisphosphonate-cadmium(II) complexes, four analytical methods were employed: potentiometry, pulse polarography (DPP), nuclear magnetic resonance spectroscopy…

Optimalization of the measuring technique in differential pulse polarography

1979

Differential Faradaic rectification polarography (DFRP)

1979

A new polarographic technique is described which is based on the determination of the Faradaic rectification effect. It will be of interest for analytical investigations and for electrode kinetics.

Electrochemical reactions with adsorption of the reactants and electrosorption. Simple analytical solutions for a Henry isotherm

1998

Abstract A theoretical treatment of an electrochemical reaction O + ne− R with adsorption of the reactants is presented when the adsorption, at equilibrium, obeys a Henry isotherm. A simple analytical solution, valid for any degree of adsorption of O and or R, is established for a polarographic wave. In LSV, for slow sweep rates and weak adsorption, both the cathodic and anodic peaks have a ‘diffusional’ character; for high sweep rates and strong adsorption, they are both of a ‘surface’ nature. In the intermediate case, one peak has a ‘diffusional’ character (deposition process), while the other is of a ‘surface’ nature (redissolution process). Expressions of the peak potentials are given i…

Inverse Polarography and Voltammetry: New Methods for Trace Analysis

1962

Inverse polarographic and voltammetric methods are surveyed. The electrochemical determination procedure is carried out by current reversal after electrolytic concentration on a working electrode. Analyses in the nanogram (ng) region (10−9 g.) are possible because the sensitivity is increased by a factor of 100 to 1000 in comparison with the usual polarographic and voltammetric methods. These methods are, therefore, of particular interestin trace analysis.

Determination of tyrosine and phenylalanine by derivatization with nitric acid and differential pulse polarography

1987

Abstract The determination of tyrosine and phenylalanine by differential pulse polarography, after separation by thin-layer chromatography and derivatization with nitric acid to form the nitro compounds, is proposed. Experimental conditions for the derivatization treatment are established and the polarographic determination is optimized.