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.