Measurements of Sulfur Isotope Composition on Ultrasmall(80 Nanomole)Sulfide and Sulfate Samples by a Modified EA-IRMS

The traditional method for sulfur isotope measurement using EA-IRMS commonly requires sulfur content greater than 2 μmol.Such a large sample size limits its application to low-S materials,the size mainly being due to ineffective utilization of sample gas,almost 99.7％of which is discarded with carrier gas through the split port of the continuous-flow interface.A modified EA-IRMS system with a gas chromatographic(GC)column and a custom-built cryogenic concentration device is used in this study.We measured six reference materials to test the performance of this method.The results were consistent with those obtained through traditional EA-IRMS.Precisions ranging from±0.24‰ to±0.76‰(1σ)can be obtained with samples equivalent to～80 nmol sulfur,which were similar to results obtained from an alternative method using an absorption column.Our improved method is a powerful tool for sulfur isotope measurement in ultrasmall sulfide and sulfate samples,which can be further applied to carbon,nitrogen and oxygen isotope analyses of samples at about 100 nmol level.