On-Line Sulfur-Isotope Determination Using an Elemental Analyzer Coupled to a Mass Spectrometer

An on-line method for S-isotope analysis is described. Samples are combusted in an elemental analyzer. SO2 is separated from other combustion gases by gas chromatography, and the gases enter the ion source of the mass spectrometer through a split interface. Integrated peak areas for %O2+ and %OZ+ are compared to the response for a standard gas sample to determine the 6% value. 6% values of samples analyzed using the on-line method correspond linearly with those achieved from the same sample prepared off-line, where Kiba reduction followed by oxidation of the sulfur to SO2 is carried out prior to S-isotope analysis against a known standard. With the described on-line method, the amount of sulfur necessary for S-isotope analysis is reduced to about 10 pg of S per analysis. The time needed for on-line preparation and measurement is less than one-third of the off-line procedure.