ANALYSIS OF SULFUR AND CARBON-ISOTOPE RATIOS IN MIXED MATRICES BY SECONDARY-ION MASS-SPECTROMETRY - IMPLICATIONS FOR MASS BIAS CORRECTIONS

The effects of mixed matrices on mass bias during the measurement of S -34/S-32 and C-13/C-12 ratios by secondary ion mass spectrometry were investigated. Four samples consisting of fine-grained mixtures of 50-9 5 wt parts per thousand carbonate, 5-50 parts per thousand iron sulfid e, and 0-5 parts per thousand iron oxide were analyzed. The measured d elta(34)S and delta(13)C values on all four samples were identical wit hin analytical error, and were identical to the values of the pure sul fide and carbonate minerals. These results indicate that, even for mat erials that are smaller than the primary ion beam contained in a matri x of different composition, it is possible to calibrate mass bias by u sing coarse-grained mineral standards. (Int J Mass Spectrom 178 (1998) 65-71) (C) 1998 Elsevier Science B.V.