Measurement of sulfur in environmental samples using the interference standard method with an O -pressurized reaction cell and a single-quadrupole inductively coupled plasma mass spectrometer.

RATIONALE

Precise and accurate analysis of trace sulfur in environmental samples is essential to understand its biogeochemical cycle. Yet it remains a challenging analytical task for single-quadrupole inductively coupled plasma mass spectrometry (ICP-MS) instrumentation because of the presence of significant isobaric interferences.

METHODS

We evaluated the effect that different instrumental parameters have on the formation of SO species, and show that, under our instrumental configuration, it is not possible to fully remove all spectral interferences. Consequently, our instrumental optimization is focused on minimizing their contribution while obtaining the best possible sensitivity. We assessed the performance of the interference standard (IFS) method, where the signal corresponding to the SO ions formed in the ICP is normalized to that of Ar .

RESULTS

We found that, by pressurizing the cell with O , there is a significant improvement in sensitivity and detection limits, associated with a more effective production and focalization of SO ions. Moreover, by applying the systematics of the IFS with pure O injected into the cell (IFS-O ) we observed a significant improvement in accuracy and detection limits, making this the method of choice for the quantification of trace sulfur in environmental samples by ICP-MS.

CONCLUSIONS

The method described here represents an effective and affordable alternative for the accurate and precise determination of sulfur using single-quadrupole ICP-MS in environmental samples, with LODs and LOQs comparable with those obtained with more expensive instrumentation.