A modified laser ablation-isotope ratio mass spectrometry method for in situ analysis of sulfur isotope composition of sulfides

Rationale: A novel laser ablation-isotope ratio mass spectrometry (LA-IRMS) method for in situ sulfur isotope analysis of sulfides has been developed. Instead of the in situ reaction applied by the traditional laser microprobe, the analyte gas preparation in this method is separated temporally and spatially from the laser ablation, resulting in improved precision and accuracy. Methods: : Our LA-IRMS system combines an ultraviolet (UV) LA system, an elemental analyzer (EA), a custom-built cryogenic concentration system, a continuous-flow interface and an IRMS. The sulfide aerosol particles generated from LA were transferred by a helium carrier gas from the ablation cell into the reaction tube and were converted into SO 2 . Then SO 2 was enriched in two cold traps and was finally introduced into the ion source of an IRMS through a continuous-flow interface. Results: : We measured three synthetic and four natural sulfide reference materials to test the performance of this method. Precisions of ±0.25-±0.64‰ (1SD, n=5) for δ 34 S values can be obtained at a spot size of 64~80 μm. Measured values and their known true values for these sulfur isotope reference materials showed good linear relationship (R 2 =0.998~0.9995) with slope of approaching unity (1.0509~1.1313). Conclusions: : Data from the measurement of reference materials showed that the precision and accuracy of our method was satisfactory. This method is a powerful tool for in situ sulfur isotope measurement of sulfides, and can be further applied to in situ carbon and oxygen isotope analyses.