DETERMINATION OF S-34-S-32 RATIOS BY FTIR SPECTROSCOPY

A new method for determining S-34:S-32 ratios using Fourier transform infrared spectroscopy has been developed. The four sulphur-containing gases SCO, H2S, SF6 and SO2 are assessed as possible compounds for the spectroscopic measurements, from which, after a consideration of available lines showing a clear isotopic shift and also of possible synthetic routes to the gas starting from a range of natural sample types, SO2 was selected for further development of the instrumental method for the isotopic ratio determination. Sulphur in the samples present as the element, as metal sulphides or as organosulphur compounds, is converted by heating with V2O5 into gaseous SO2, and a part of the 518 cm(-1) band is recorded in the absorbance mode. The optimisation of instrumental parameters and of the chemical reaction conditions is described, and the results from the application of the method to the measurement of the level of enrichment of S-34 in a soil fungus are presented. The agreement between results at the natural abundances of 4.2% was better than 0.04% absolute for a sample size of 1.5 mg of sulphur.