1. The usual method for mass spectrometric isotopic analysis of sulfur uses an electron-impact ion source in gas-type machines. Samples in the form of SO2are usually used. When the sample to be measured is in the form of a sulfate, sulfur dioxide is produced by a laborous procedure consisting of the reduction of the suifate to a sulfide by heating with carbon 1 or by refluxing with an appropriate reducing mixture 2 and then combusting the sulfide to SO2in a stream of oxygen. This method requires rather large amounts of the sample and a special apparatus for the production of SO2.