Electrochemical oxidation of isothiazolinone biocides and their interaction with cysteine

Abstract

This paper presents voltammetric studies on carbon electrodes (linear-sweep cyclic voltammetry and differencial pulse voltammetry) on the electrooxidation of methylisothiazolinone (MIT), Chloromethylisothiazolinone (CMIT) and 4,5-dichloro-2-octyl-4-isothiazolin-3-one (DCOIT). The oxidation products have been identified after electrolysis of the compounds using liquid-liquid extraction and gas chromatography coupled to mass spectrophotometry. The identified compounds for the three biocides correspond in all cases to two-electron processes, with opening of the ring. Adsorption processes were observed for CMIT. From the differential pulse voltammetric results a general reaction pathway is proposed in which the rate-determining step is a chemical reaction placed after the first partially irreversible electron transfer. The interaction of cysteine with MIT and CMIT was studied by differential pulse voltammetry in order to quantify them and the 1:3 mixture. The specificity of the interaction with cysteine and the low values of the peak potentials minimize the interferences. The quantification is made from the decrease of the oxidation signal of cysteine as the biocide concentration increases, being the method adequate for the study of usual cosmetic and household products.