Stable isotope mass fragmentography: identification and hydrogen-deuterium exchange studies of eight Murchison meteorite amino acids

Abstract

The concentration of eight protein amino acids found in extracts of the Murchison carbonaceous chondrite has been measured by quadrupole mass fragmentography. This result was obtained by using deuterated amino acids as internal standards. In addition, hydrogendeuterium exchange in amino acids was studied by two methods. First, nondeuterated amino acids were added to the meteorite and the amount of deuterium incorporated after extraction with deuterium oxide was determined. Second, deuterated amino acids were added to the dry meteorite and the loss of deuterium after extraction with H 2O was measured. It was observed that the degree of hydrogen-deuterium exchange increased with increasing severity of extraction conditions. This exchange resulted in some racemization, presumably catalyzed by constituents of the meteorite. The degree of racemization for each amino acid was determined by gas chromatography of the corresponding N-trifluoroacetyl-O-( + )-2-butyl esters.