Determination of Unbiased δ34S and Δ33S Values by MC-ICP-MS Using Down to 30 nmol of Sulfur

Abstract

The multi-collector inductively coupled plasma-mass spectrometer is an instrument suited to measuring sulfur isotopes in all types of samples, from ice cores and river waters to carbonates and Archaean rocks. Its main advantage is the more convenient method of sample preparation, as sulfate does not need to be reduced but purified from the sample through ion exchange. This method allows the measurement of unbiased and precise δ³⁴S values from samples as small as 10-nmol with a typical intermediate precision of 0.15‰ (2s) at 95% confidence. So far, no attempt has been made to understand at which levels of analytical precision and bias MC-ICP-MS could provide ∆³³S values. Here, the first standard addition experiment undertaken for ∆³³S evaluation shows that measurement results on a Neptune Plus MC-ICP-MS allows us to calculate ∆³³S values identical to those established by other measurement principles, for samples down to 30 nmol S, with an intermediate precision as good as 0.05‰ (2s). Though this precision is not as good as the analytical precision of data acquired by the SF₆ method, the advantages of small sample size and straightforward sample handling make it a very useful tool for investigating past and modern aspects of the sulfur cycle.