Determination of δ13C, δ15N, or δ34S by isotope-ratio-monitoring mass spectrometry using an elemental analyzer

This report describes procedures used in the Geology, Geophysics, and Geochemistry Science Center of the U.S. Geological Survey in Denver, Colorado, to determine the stable-isotope ratios ¹³C/¹²C, ¹⁵N/¹⁴N, and ³⁴S/³²S in solid materials. The procedures use elemental analyzers connected directly to gas-source isotope-ratio mass spectrometers. A different elemental–analyzer–mass-spectrometer system is used for ¹³C/¹²C and ¹⁵N/¹⁴N than is used for ³⁴S/³²S to accommodate differences in reagents, catalysts, and instrument settings.