Sulfur isotope analysis of sulfide and sulfate minerals by continuous flow-isotope ratio mass spectrometry

A continuous now method (CF-IRMS) for the rapid determination of the sulfur isotope composition of sulfide and sulfate minerals has significant advant ages over the classic extraction method in terms of the reduced sample quan tity and a rapid analytical cycle of less than 8 min/analysis. For optimum performance, the technique is sensitive to a number of operating parameters , including sample weight and the O-2 saturation of the Cu-reduction reacto r. Raw data are corrected using a calibration based on five international a nd internal standards ranging from -17.3 to +20.3 parts per thousand, which requires monitoring in order to correct the effect of changing delta O-18 of the sample gas on the measured mass 66 values. Measured sulfur contents are within 1-1.5% of expected values and the reproducibility of delta S-34 values is +/-0.1 parts per thousand (1 sigma). The technique has been used successfully for more than 1000 analyses of geological samples with a wide range of delta S-34 from -20 to +20 parts per thousand.