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A study was undertaken to determine the effect of Cu(II) in degradation of methylparathion (o,o-dimethyl o,4-nitrophenyl phosphoriotioate) in acid medium. Initial electrochemical characterization of Cu(II) and methylparathion was done in an aqueous medium at a pH range of 2-7. Cu(II) was studied in the presence of different anions and it was observed that its electroactivity depends on pH and is independent of the anion used. Methylparathion had two reduction signals at pH < or = 6 and only one at pH > 6. The pesticide's transformation kinetic was then studied in the presence of Cu(II) in acid buffered aqueous medium at pH values of 2, 4, and 7. Paranitrophenol appeared as the only electroactive product at all three pH values. The reaction was first order and had k values of 5.2 x 10(-3) s(-1) at pH 2, 5.5 x 10(-3) s(-1) at pH 4 and 9.0 x 10(-3) s(-1) at pH 7. It is concluded that the principal degradation pathway of methylparathion in acid medium is a Cu(II) catalyzed hydrolysis reaction.

Arnica montana is a medicinal plant. Its biological activity is related to carboxyphenolic acids such as caffeic acid. This paper proposes a caffeic acid quantification method of Arnica montana tinctures by lineal sweep voltammetry with a platinum rotating disc electrode. Tinctures showed a number of electrochemical signals; two of them corresponding to caffeic acid oxidation. One of these signals was found to be controlled by a diffusion process and was used to quantify caffeic acid in the tinctures. The caffeic acid detection limit was established at 385 mg L À1 , and tincture concentration ranged from 161 to 265 mg L À1 .