title: Accurate determination of sulfur in gasoline and related fuel samples using isotope dilution ICP-MS with direct sample injection and microwave-assisted digestion.
abstract: Inductively coupled plasma isotope-dilution mass spectrometry (ICP-IDMS) with direct injection of isotope-diluted samples into the plasma, using a direct injection high-efficiency nebulizer (DIHEN), was applied for accurate sulfur determinations in sulfur-free premium gasoline, gas oil, diesel fuel, and heating oil. For direct injection a micro-emulsion consisting of the corresponding organic sample and an aqueous 34S-enriched spike solution with additions of tetrahydronaphthalene and Triton X-100, was prepared. The ICP-MS parameters were optimized with respect to high sulfur ion intensities, low mass-bias values, and high precision of 32S/34S ratio measurements. For validation of the DIHEN-ICP-IDMS method two certified gas oil reference materials (BCR 107 and BCR 672) were analyzed. For comparison a wet-chemical ICP-IDMS method was applied with microwave-assisted digestion using decomposition of samples in a closed quartz vessel inserted into a normal microwave system. The results from both ICP-IDMS methods agree well with the certified values of the reference materials and also with each other for analyses of other samples. However, the standard deviation of DIHEN-ICP-IDMS was about a factor of two higher (5-6% RSD at concentration levels above 100 mircog g(-1)) compared with those of wet-chemical ICP-IDMS, mainly due to inhomogeneities of the micro-emulsion, which causes additional plasma instabilities. Detection limits of 4 and 18 microg g(-1) were obtained for ICP-IDMS in connection with microwave-assisted digestion and DIHEN-ICP-IDMS, respectively, with a sulfur background of the used Milli-Q water as the main limiting factor for both methods.
authors.affiliation: Institute of Inorganic Chemistry and Analytical Chemistry, Johannes Gutenberg-University, Duesbergweg 10-14, 55099 Mainz, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Heilmann
authors.forename: Sergei F
authors.initials: SF
authors.lastname: Boulyga
authors.forename: Klaus G
authors.initials: KG
authors.lastname: Heumann
mesh_terms: D005648:Fuel Oils / Q000032:analysis*; D005742:Gasoline / Q000032:analysis*; D007477:Ions; D007554:Isotopes / Q000737:chemistry; D013058:Mass Spectrometry / Q000379:methods; D008872:Microwaves; D009330:Nebulizers and Vaporizers; D013455:Sulfur / Q000032:analysis*
chemical_list: D005648:Fuel Oils; D005742:Gasoline; D007477:Ions; D007554:Isotopes; D013455:Sulfur