Sulfur determination by laser ablation high resolution magnetic sector ICP-MS applied to glasses, aphyric lavas, and micro-laminated sediments

Sulfur (S) is an important element for understanding redox processes, ore formation, environmental chemistry, volcanism and climate. Here, we present a method for in situ S concentration measurement by LA-ICP-MS at the 50-100 mu m length scale using a 213 nm laser ablation set up coupled to a single-collector magnetic sector ICP-MS with high resolution capabilities. Analyses were performed in medium mass resolution (m/Delta m = 3000) mode, which allows for the separation of S-32 and S-34 from molecular interferences. S is simultaneously analyzed along with all major and minor elements so that a priori knowledge of an internal standard concentration is not necessary; this allows for in situ bulk analysis of aphyric groundmass in volcanic rocks or other fine-grained samples. The primary limitation in analyzing S by laser ablation was found to be long-term instrumental drift in fractionation of elemental S relative to other elements, presumably due to drift in laser dynamics. A method for correcting for such fractionation over time was implemented. After correcting for such drift, measurements of homogeneous basaltic glasses are reproducible to within 10 % for high concentration samples (>500 ppm) and to within 20 % for low concentration samples (<200 ppm). The applicability of the method was demonstrated using natural and synthetic glasses, aphyric lavas, and micro-laminated sediments.