Search results for "Polarography"
showing 10 items of 46 documents
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.
Use of polarography as a quality-control method for determining diacetyl in citrus and vegetable juices, yoghurt and butter
2002
The determination of diacetyl permits the detection of microbial growth in the processing of citrus fruit before the appearance of other organoleptic, chemical or microbiological changes. It also makes it possible to detect a break in the cold chain during distribution and sale. The study proposed a polarographic method for the determination of diacetyl that allowed routine analysis with the aim of detecting possible contamination in the citrus juice manufacturing chain (orange and orange-carrot). The analytical performance of the method in terms of a linearity from 0 to 960 microg ml(-1), a recovery of 97 to 98%, a precision of 3.2 to 4.8%, and a sensitivity of 0.2 ng ml(-1) for juices ind…
Toward a Quality Guide to Facilitate the Transference of Analytical Methods from Research to Testing Laboratories: A Case Study
2009
Abstract At present, there is no single viewpoint that defines QA strategies in analytical chemistry. On the other hand, there are no unique protocols defining a set of analytical tasks and decision criteria to be performed during the method development phase (e.g., by a single research laboratory) in order to facilitate the transference to the testing laboratories intending to adapt, validate, and routinely use this method. This study proposes general criteria, a priori valid for any developed method, recommended as a provisional quality guide containing the minimum internal tasks necessary to publish new analytical method results. As an application, the selection of some basic internal qu…
The electrochemical reduction of thioisonicotinamide in an aqueous medium
1998
Abstract The electrochemical reduction of thioisonicotinamide NRCSNH 2 has been examined in an aqueous medium between H 0 =−1 and pH=13.7. As shown by cyclic voltammetry and polarography, a global 2e − reversible transfer is followed by two successive first-order chemical reactions and a 2e − , 2H + reduction (EC 1 C 2 E process). A mechanism is proposed, beginning with the 2e − reduction of NRCSNH 2 to the formal diionized form NRC − (SH)(NH 3 + ), the first chemical reaction, C 1 , being a formal proton transfer which yields the 4- gem aminosulfanylmethylpyridine; the rate constant of this reaction is 2×10 4 s −1 in acidic medium and diminishes in neutral medium. The second process, C 2 …
Polarographische Untersuchungen an monomeren und polymeren N-Chlorcarbonamiden
1979
The polarographic reduction of low molecular and high molecular N-chlorocarboxamides at the dropping mercury electrode proceeds in two one-electron-transfer steps, which are highly irreversible. In the case of the low molecular models 1 and 2 the reaction is diffusion-controlled, whereas in the case of the poly(N-chloroamide) 3 the reaction is adsorption-controlled. Reduction of several poly(N-chloroamide)s shows always two reduction waves with a distance of 0,5 V. There is, however, no relation between the polyamide-type and the position of the half-wave potentials. The polarographic reduction can be used as an analytical method for quantitative determination of N-chlorocarboxamide groups …
Stratégies de contrôle pour la manipulation spatiale de molécules
2011
Talk given by E. Hertz; National audience
Two fungal lanostane derivatives as phospholipase A2 inhibitors.
1996
The hydroalcoholic extract of Poria cocos and two lanostane derivatives isolated from it, pachymic acid (1) and dehydrotumulosic acid (2), were active as inhibitors of phospholipase A2 from snake venom when a polarographic method was used. Dehydrotumulosic acid exhibited an IC50 of 0.845 mM. These two compounds are structurally related to certain triterpenoids from Ganoderma and Schinus that have previously been described as competitive inhibitors of phospholipase A2. These comprise a new group of natural potential antiinflammatory agents due to their interaction with that enzyme.
Optimalization of doubletone polarography
1977
Abstract Through the application of coherent fundamental frequencies, the synchronization of measuring frequency and dropping frequency, which facilitate the use of phase sensitive techniques, doubletone polarography could be developed into a highly sensitive polarographic method with a high resolution in common with all derivative methods.