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 advantages over the classic extraction method in terms of the reduced sample quantity 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 reactor. Raw data are corrected using a calibration based on five international and 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.