DERIVATIZATION OF ORGANIC-COMPOUNDS PRIOR TO GAS-CHROMATOGRAPHIC COMBUSTION-ISOTOPE RATIO MASS-SPECTROMETRIC ANALYSIS - IDENTIFICATION OF ISOTOPE FRACTIONATION PROCESSES

An examination of the practice of derivatizing organic compounds such as fatty acids, sterols and amino acids in relation to subsequent anal ysis via gas chromatography-combustion-isotope ratio mass spectrometry is presented. Fractionation processes, such as kinetic isotope effect s, which cause a deviation in the measured stable carbon isotope ratio s (delta-values) of derivatized compounds from simple mass balance con siderations are examined. Particular attention is paid to reactions th at proceed by the cleavage of a carbon-containing bond and reactions t hat are likely to have kinetic isotope effects associated with them, s uch as acetylation and diazotization. Isotope fractionation processes other than those which are kinetic based are also discussed, as is the additional imprecision of the calculation of the delta-values of samp le compounds inherent when derivative carbon is added. Failure to take this imprecision into account when comparing delta-values could lead to erroneous conclusions with respect to the magnitude of kinetic isot ope effects caused by derivative reactions.