Extracted ion chromatograms for m/z 348 under two conditions of sample preparation in the urine sample. When no acids were used in workup procedure, four peaks 1, 2, f and g were observed (top EIC). In the urine samples diluted with equal volume of 1% formic acid (v/v), peaks 1 and 2 were degraded resulting in a single large peak corresponding to f and g (bottom EIC). A representative mass spectrum for peak 1 showing abundance of masses of ions m/z 366 and m/z 348. The spectra of peak 2 was similar to peak1. This fragmentation pattern suggested that 1, 2, f, and g are putative mercapturic acids metabolites. MS analysis was carried out by LCQ deca.