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

RationaleA novel laser ablation-isotope ratio mass spectrometry (LA-IRMS) method for in situ analysis of sulfur isotopes in 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 LA, resulting in improved precision and accuracy.MethodsOur LA-IRMS system combines an ultraviolet 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 then converted into SO2. Subsequently, SO2 was enriched in two cold traps and was finally introduced into the ion source of the IRMS through the continuous-flow interface.ResultsWe measured three synthetic and four natural sulfide reference materials to test the performance of this method. Precisions of +/- 0.25 parts per thousand-+/- 0.48 parts per thousand and +/- 0.32 parts per thousand-+/- 0.64 parts per thousand (1SD, n = 5) for delta 34S values of synthetic and natural sulfide standards can be obtained for spot sizes ranging from 64 to 80 mu m. Measured values and their recommended values showed a good linear relationship (R2 within 0.998 and 0.9995) with the slope of approaching unity (within 1.0509 and 1.1313).ConclusionsData from the measurement of reference materials showed that the precision and accuracy of our method were 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.