As(III)-GS3 and methylarsinous acid-GSH (MA(III)-GS2), m/z traces of GSH and As(III)-GS3 and MA(III)-GS2 measured by ESI-MS and m/z 75 (As) measured by ICP-MS. Separation, MeOH/formic acid gradient on C18 ODS2 column, the broad m/z 75 peak under the eluting As(III)-GS3 and MA(III)-GS2 signals is a result of the presence of γ-Glutamylcysteinylglycinyl)di-methylthioarsinite (DMA(III)-GS) in the mixture, which is not stable under these chromatographic conditions (*, unknown species; #, species identified as mentioned in trace).