ANALYSIS OF TERT.-BUTYLDIMETHYLSILYL [1-C-13]PALMITIC ACID IN STOOL SAMPLES BY GAS CHROMATOGRAPHY-MASS SPECTROMETRY WITH ELECTRON-IMPACT IONIZATION - COMPARISON WITH COMBUSTION ISOTOPE-RATIO MASS-SPECTROMETRY

The use of C-13-labelled compounds to study lipid metabolism is increa sing. Typically less than 40% of the orally administered label is reco vered in breath CO2. The remainder must be either absorbed and not oxi dised or not absorbed and remain in the faeces. Two methods of determi ning how much tracer passes through the body, and is present in the st ool, were compared. Compound specific analysis of tert.-butyldimethyls ilyl [C-13]hexadecanoic acid by gas chromatography-mass spectrometry ( GC-MS) with electron impact ionisation was compared with bull; analysi s of whole stool and lipid extract by continuous flow isotope ratio ma ss spectrometry (CF-IRMS) with a combustion interface. The mean differ ence between the IRMS and GC-MS methods was -0.02 mmol C-13 d(-1) with a mean excretion of 14.2 mmol C-13 d(-1). Combustion IRMS is both sim pler and cheaper, when the objective is to determine how much administ ered dose appears in steal, and information about the form of the labe l is not required. (C) 1998 Elsevier Science B.V. All rights reserved.