Measurement of the content of sulfur in gas oils using a high pressure asher, isotope dilution and thermal ionization mass spectrometry

Abstract

A new method has been developed for the measurement of sulfur in gas oils using a high pressure asher (HPA) for sample digestion. This, combined with a calibrated enriched isotopic reference material, and high precision mass spectrometry, makes it a powerful tool for an accurate and precise determination of the sulfur content in fossil fuels. The method described here was one of the methods used in the certification of the candidate reference materials BCR-104R, BCR-671 and BCR-672. Approximately 0.2 g of the gas oil samples were spiked with the spike isotopic reference material IRMM-646, which is enriched in ³⁴S, and combusted in an HPA using nitric acid. The isotopes of sulfur were measured as arsenic monosulfides (AsS⁺) using a thermal ionization mass spectrometer equipped with a Faraday detector. The total uncertainty of the sulfur content (k = 2) is about 1%. The certified reference materials NIST SRM-2724b and NIST SRM-1619b and BCR-105 were used as part of the method validation work. The mass content of sulfur in BCR-104R was measured to be 1014 µg g⁻¹, BCR-671 has 450 µg g⁻¹ sulfur and BCR-672 shows a sulfur mass content of 201 µg g⁻¹. The sulfur content of the candidate reference materials is homogeneous for the sample size used.