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 avai lable lines showing a clear isotopic shift and also of possible synthe tic routes to the gas starting from a range of natural sample types, S O2 was selected for further development of the instrumental method for the isotopic ratio determination. Sulphur in the samples present as t he element, as metal sulphides or as organosulphur compounds, is conve rted 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 instru mental parameters and of the chemical reaction conditions is described , and the results from the application of the method to the measuremen t of the level of enrichment of S-34 in a soil fungus are presented. T he agreement between results at the natural abundances of 4.2% was bet ter than 0.04% absolute for a sample size of 1.5 mg of sulphur.