Determination of sulfur in ferroalloys, iron ores and pig irons by isotope dilution-spark source mass spectrometry

The determination of sulfur in ferroalloys, iron ores and pig irons by the isotope dilution method using 34S enriched sulfur, combined with spark source mass spectrometry, was studied. This method is based on a conventional gravimetric method. Samples were dissolved in nitric and hydrochloric axid containing potassium chlorate and the spike solution which was prepared by dissolving elemental 43S in nitric acid, and potassium chlorate was added to the solution. For ferrosilicon and high-carbon ferrochrome samples, they were fused with sodium carbonate or sodium carbonate and sudium peroxide. The resulting solution was evaporated to dryness. These salts were dissolved in hydrochloric acid, and metallic zinc was added to reduce ferric ions to ferrous ions. Barium chloride was added to the solution to precipitate sulfur as barium sulfate, and then the precipitate was filtered and ignited. The ignited residue was mixed with graphite powder and pressed into electrodes. The method was applied to the determination of sulfur in the JSS, NBS and BCS standard samples, and the results with satisfactory precision and accuracy were obtained for the analyzed samples except for ferrosilicon samples. The poor precision for ferrosilicon seems to be due to the blank of sulfur from reagents (Na2O2, etc.) used. (author)