| Analytical Geochemistry, an important part of modern geochemistry, is an interdisciplinary subject of earth and analytical chemistry. This subject provides the elements or compounds composition information in geological samples for geologists, using chemical analysis as tool. Geochemical analysis is an important foundation of the contemporary earth science research, mineral resources and geological environment evaluation. The development of geochemical analysis closely relates to the needs of the development of modern earth science.For many decades Inductively Coupled Plasma Mass Spectrometry (ICP-MS) has occupied an outstanding position among the analytical techniques due to its universality, high sensitivity and wide fields of application in element analysis, especially in the determination of trace and isotope ratio measurements. In this study, we introduce an analytical method of in situ determination of sulfur isotopes using LA-MC-ICP-MS in sulfides and elemental sulfur.Sulfur isotope is an important geochemical tracer in diverse fields of geosciences. In this study, the effects of three different cone combinations with the addition of N2 on the performance of in situ S isotopes analyses were investigated in detail. The signal intensities of S isotopes were improved by a factor of 2.3 and 3.6, respectively, with use of the X skimmer cone in combination with the standard sample cone or the Jet sample cone compared to the standard arrangement (H skimmer cone in combination with the standard sample cone). This signal enhancement is important for the improvement of the precision and accuracy of in situ S isotope analysis at high spatial resolution. Different cone combinations have a significant different effect on the mass bias and mass bias stability for S isotopes. Poor precisions of S isotope ratios were obtained using the Jet and X cones combination at their corresponding optimum makeup gas flow when using Ar plasma only. The addition of 4-8 ml/min nitrogen to the central gas flow in laser ablation MC-ICP-MS was found to significantly enlarge the mass bias stability zone at their corresponding optimum makeup gas flow in these three different cone combinations. The polyatomic interferences of OO, SH, OOH were also dramatically reduced, and the interference free plateaus of sulfur isotopes became broader and flatter in the nitrogen mode (N2=4 ml/min). However, the signal intensity of S was not found to be increased by the addition of nitrogen in this study. Laser fluence and ablation mode had significant effects on sulfur isotope fractionation during analysis of sulfides and elemental sulfur by laser ablation MC-ICP-MS. Matrix effect among different sulfides and elemental sulfur was observed, but it could be significantly reduced by using the line scan ablation instead of single spot ablation under the optimized fluence. It is recommended that the d90(particle size for 90% of the sample) values of the particles in pressed powder pellets for accurate and precise S isotope analysis should be less than <10 μm. With selected optimized analytical conditions, excellent agreements between the determined values and the reference values were achieved for the IAEA-S series AgS2 standard reference materials (IAEA-S-1, IAEA-S-2, IAEA-S-3, IAEA-S-4, GBW04414, GBW04415) and a set of five well-characterized, isotopic homogeneous natural sulfide standards (PPP-1, MASS-1, MoS2, P-GBW07267, P-GBW07268, P-GBW07270), validating the capability of the developed method for providing high-quality in situ S isotope data in sulfides and elemental sulfur. |
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