Development of a Species-Unspecific Isotope Dilution GC−ICPMS Method for Possible Routine Quantification of Sulfur Species in Petroleum Products

Inductively coupled plasma mass spectrometry (ICPMS) hyphenated with capillary gas chromatography was applied for sulfur multispecies determination in petroleum products by species-unspecific isotope dilution mass spectrometry (IDMS). To guarantee a stable and continuous addition of the spike into the GC−ICPMS system, a special dosing unit was designed and synthesis of a 34S-labeled dimethyldisulfide spike from 34S-enriched elemental sulfur in the milligram range was developed. The sample was mixed with an internal standard for spike mass flow calibration. From the mass flow chromatogram obtained by species-unspecific GC−ICP-IDMS, determination of all separated sulfur species and of the total sulfur content was possible without any matrix influence by coeluting hydrocarbons. The accuracy of the developed method was evaluated by determining reference material SRM-2296 certified for three sulfur species and by comparison of results obtained by species-specific GC−ICP-IDMS. The total sulfur concentration determined for all separated species agreed well with the sulfur content in the original samples which demonstrated that all sulfur species have been covered. Structural characterization of sulfur species was carried out by corresponding sulfur standards and by applying electron ionization ion trap mass spectrometry. The low detection limit of 9 ng sulfur per gram sample, independent of results on coeluting hydrocarbons, and the robust instrumental design of the continuous spike flow dosing unit qualifies this species-unspecific GC−ICP-IDMS method for accurate and sensitive sulfur multispecies determinations also on a routine basis.