Precise and accurate determination of high concentrations of sulphur by isotope-dilution thermal-ionization mass-spectrometry

An isotope-dilution thermal-ionization mass-spectrometric procedure has been developed for the accurate and precise determination of sulphur in steels and organic-based materials. The sample and isotopically enriched sulphur spike are dissolved in a sealed tube to prevent loss of sulphur and the sulphur isotopes are measured as AsS⁺ ions, with silica gel as an emitter. This technique has been applied to the determination of sulphur in 13 NBS Standard Reference Materials ranging in concentration from 0.03 to 5% S. The relative uncertainty for a single determination is typically 0.5% (95% confidence interval) and arises primarily from the uncertainty in the spike calibration and from sample inhomogeneity.