Oxidation of DMSO and methanesulfinic acid by the hydroxyl radical

The quantitation of methanesulfinic acid, the reaction product of dimethylsulfoxide oxidation by the hydroxyl radical, has been reported as a useful tool for the detection of this radical. The present report describes two HPLC methods for determination of methanesulfinate. The first is based on the reversed phase separation and detection of the derivative formed between methanesulfinate and the diazonium salt fast garnet GBC. The second is based on anion exchange HPLC using conductivity detection. In incubations containing xanthine plus xanthine oxidase, the formation of the hydroxyl radical was demonstrated by trapping with DMSO and detection of methanesulfinate. Formation of the sulfinate from DMSO did not occur in the presence of catalase or with the omission of xanthine oxidase. In the absence of xanthine oxidase, methanesulfinate added as an internal standard could be completely recovered. In the presence of of xanthine oxidase, however, the recovery of added methanesulfinate was less than 40%. Using the Fenton reaction to generate these radicals, both methanesulfinate and methanesulfonate were formed in the presence DMSO. In incubations with methanesulfinate, hydroxyl radical generation led to stoichiometric loss of methansulfinate and production of methanesulfonate. Methanesulfinate was only slowly oxidized to methanesulfonate in incubations containing hydrogen peroxide in the absence of iron. The data illustrate that the product of DMSO oxidation by the hydroxyl radical, methanesulfinate, is further oxidized by this radical to methanesulfonate. Determination of methanesulfinate formation from DMSO underestimates the production of the hydroxyl radical.