Volume 6, Issue 1, 1988
8th January, 2023
Recent Advances in Direct Potentiometry in Organic and Mixed Solvents
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by G. J. Kakabadse, M. Al-Aziz, N. F. N. Al-Yawer et al.
5-25
DOI: DOI: 10.4152/pea.198801005
The behaviour of ions in organic and mixed solvents is illustrated by a number of examples. Systematic study of the effect of solvent on potentials of cells with ion-selective electrodes led to the development by Kakabadse and co-workers of a new technique in direct potentiometry, viz. the ion isoconcentration technique (IICT). In IICT, concentration of solvent is varied and that of indicator ion is kept constant. Many simple mixtures show under ion isoconcentration conditions a systematic change of cell potential with variation in the concentration of organic solvent, providing a graphical method for the rapid determination of, (a) individual organic solvents in simple mixtures, and (b) residual water in organic solvents.
A laboratory prototype monitor for the continuous determination of ethanol in cider and sherry, using the fluoride isoconcentration technique (FICT), is described.
Electrochemical Behaviour of the Mesoinic Heterocycle: Anhidro l-Amino-5-Phenyl-2-Mercapto-l,3, 4-Triazolo-(3,2-c)-Quinazolin-4-ium
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by F. Martinez-Ortiz, J. Vera, M.A. Esteso
27-40
DOI: DOI: 10.4152/pea.198801027
An electrochemical study on the mesoionic heterocycle mentioned above is carried out, using dc polarography, cyclic voltammetry and controlled potential electrolysis . A reduction mechanism
with a consumption of four electrons in each polarographic wave is proposed. On the other hand, we detect a kinetic response of CE type caused by an equilibrium between hydrolysis products ot the heterocycle.
Temperature Effect on Polarogra-phic Behaviour of Co(II) and Zn(II) 2:1 Complexes with Paludrine
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by C. Sanz Box, C. Monleón Ombuena, F. Vicente Pedrós
41-50
DOI: DOI: 10.4152/pea.198801041
The polarographic reduction of Zn(II> and Co(II) complexes with paludrine has been studied in moderated acid media. The Zn(II) 2:1 complex shows two well defined waves. The Co(II) 2:1 complex shows only one wave. Arrhenius activation energies, obtained from diffusion currents of np, dp, aci , aca, KT and K-L- polarograms, show that all cathodic and anodic processes are controlled by diffusion. The mechanism of these processes is proposed.
The Effect of Adatoms on the Reversibility of some Redox Couples
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by Inês T.E. Fonseca, A.C. Marin
51-68
DOI: DOI: 10.4152/pea.198801051
Cyclic voltammetric studies were performed for six redox couples at a Pt electrode, in the absence and in the presence of Bi, Pb and Cd adatoms. Standard rate constants were evaluated for all the systems in the absence and in the presence of adatoms.
Whenever a catalytic effect was obtained the effect of coverage was studied in a quantitative way.It was found that the rate constant increases initially rapidly and then passes through a maximum or reaches a constant value, at coverages of the order of a monolayer. For all the systems the influence of the adatoms decreases in the order Bi > Pb > Cd.
Eléctrodo Sensível ao Anião 5,5-Dietilbarbiturato com Membrana de PVC sem Solução de Referência Interna com Sensor de Tetraoctilamónio em 2-Nitrofeniloctiléter
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by José L. F. C. Lima, M. Conceição B. S. M. Montenegro et al.
69-76
DOI: DOI: 10.4152/pea.198801069
