Fig. 5. GC/MS analysis of organic fluoroacids, derived from β-lyase–catalyzed metabolism of compound A S -conjugates, in human urine. ( A ) Selected-ion mode chromatograph ( m/z 342, 310, 294) of a diphenyldiazomethane-derivatized extract of urine from a patient undergoing low-flow sevoflurane. The 3,3,3-trifluoro-2-(fluoromethoxy)propanoic acid and trifluorolactic acid peaks at 16.4 and 16.2 min, respectively, were not present in urine obtained before anesthesia (not shown). ( B ) Mass spectrum of the 16.4-min peak in ( A ), which was identical to synthetic 3,3,3-trifluoro-2-(fluoromethoxy)propanoic acid diphenylmethyl ester.