Use of ring-disc electrodes for the determination of aqueous solutions of sulphur-containing compounds: thiols, disulphides, sulphides, thiol-esters, proteins and various inorganic ions

International audienceWe examined the possibility of using nascent bromine and iodine, generated and detected on ring-disc electrodes, for the titration of aqueous solutions of thiols (ethanethiol, 2-methyl-2-propanethiol, ethanedithiol, 1,3-propanedithiol, glutathione, ergothioneine, coenzyme-A), disulfides (dimethyl-and diethyldisulfide, cystine, oxidized form of glutathione and of lipoïc acid), sulfides (diethylsulfide, methionine), thiolesters (ethylthiol acetate, acetylcoenzyme-A) and various inorganic sulfur-containing compounds (sulfhydric acid, sulfite and thiosulfate). According to the shape of ring current vs disc current curves, which is related to the rate of the reaction involved in the titration, we used different methods to analyse these curves and to determine the concentration of the compound. Most of them can be detected at a concentration as low as 0.1 µM and titrated with a few per cent accuracy when their concentration is larger than 5 µM. We discuss the influence of pH on the characteristics of the titration curves