STABLE CARBON-ISOTOPE COMPOSITIONS OF INDIVIDUAL AMINO-ACID ENANTIOMERS IN MOLLUSK SHELL BY GC C IRMS

Gas chromatography/combustion/isotope ratio mass spectrometry was used to determine the stable carbon isotope composition of D- and L-enanti omers of amino acids in a fossil Mercenaria shell and in modem samples of Helix pomatia shell that were heated (80-degrees-C) for up to 289 days. The similarity in deltaC-13 values for the D- and L-enantiomers of neutral amino acids in Mercenaria implies that these components are indigenous. Whereas differences in the C-13 contents of the D- and L- enantiomers of aspartic and glutamic acid in Mercenaria may indicate i nputs from exogenous sources, similar discrepancies exist for the acid ic amino acids in the heated samples of H. pomatia, suggesting more co mplicated diagenetic pathways and concomitant isotope effects for the acidic amino acid constituents of shell protein.