A rapid and high-precision method for sulfur isotope δ~(34)S determination with a multiple-collector inductively coupled plasma mass spectrometer: matrix effect correction and applications for water samples without chemical purification

摘要

RATIONALE: Previous studies have indicated that prior chemical purification of samples, although complex and timeconsuming, is essential in obtaining precise and accurate results for sulfur isotope ratios using multiple-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). In this study, we introduce a new, rapid and precise MC-ICP-MS method for sulfur isotope determination from water samples without chemical purification. METHODS: The analyticalworkwas performed on anMC-ICP-MS instrumentwith mediummass resolution (m/Δm~ 3000). Standard-sample bracketing (SSB) was used to correct samples throughout the analytical sessions. Reference materials included an Alfa-S (ammonium sulfate) standard solution, ammonium sulfate provided by the lab of the authors and fresh seawater from the South China Sea. A range of matrix-matched Alfa-S standard solutions and ammonium sulfate solutions was used to investigate the matrix (salinity) effect (matrix was added in the form of NaCl). A seawater sample was used to confirm the reliability of the method. RESULTS: Using matrix-matched (salinity-matched) Alfa-S as the working standard, the measured δ~(34)S value of AS (-6.73 ± 0.09‰) was consistent with the reference value (-6.78 ± 0.07‰) within the uncertainty, suggesting that this method could be recommended for the measurement of water samples without prior chemical purification. The δ~(34)S value determination for the unpurified seawater also yielded excellent results (21.03 ± 0.18‰) that are consistent with the reference value (20.99‰), thus confirming the feasibility of the technique. CONCLUSIONS: The data and the results indicate that it is feasible to use MC-ICP-MS and matrix-matched working standards tomeasure the sulfur isotopic compositions ofwater samples directlywithout chemical purification. In comparison with the existingMC-ICP-MS techniques, the new method is better for directly measuring δ~(34)S values in water samples with complex matrices; therefore, it can significantly accelerate analytical turnover.