Improved analysis of micro- and nanomole-scale sulfur multi-isotope compositions by gas source isotope ratio mass spectrometry

David Au Yang; Guillaume Landais; Nelly Assayag; David Widory; Pierre Cartigny

doi:10.1002/rcm.7513

Improved analysis of micro- and nanomole-scale sulfur multi-isotope compositions by gas source isotope ratio mass spectrometry

Rapid Commun Mass Spectrom. 2016 Apr 15;30(7):897-907. doi: 10.1002/rcm.7513.

Authors

David Au Yang^{1

2}, Guillaume Landais¹, Nelly Assayag¹, David Widory², Pierre Cartigny¹

Affiliations

¹ Laboratoire de Géochimie des Isotopes Stables, Institut de Physique du Globe de Paris, Université Paris Diderot, CNRS UMR 7154, Sorbonne Paris-Cité, 1 rue de Jussieu, 75005, Paris, France.
² GEOTOP/Université du Québec à Montréal (UQAM), Montréal, H3C 3P8, Canada.

PMID: 26969932
DOI: 10.1002/rcm.7513

Abstract

Rationale: Multiple sulfur isotope compositions are usually measured on relatively large samples (in the range of micromoles); however, sometimes only small amounts are available and thus it is necessary to analyze small (sub-micromole) samples. We report an improved method to measure multiple sulfur isotope compositions: δ(33) S, δ(34) S and δ(36) S values on the SF6 molecule (m/z 127, 128, 129, 131) for quantities down to 0.1 micromole, and δ(33) S and δ(34) S values for quantities down to 20 nanomoles.

Methods: Multiple sulfur isotope analyses including fluorination and purification of two international Ag2 S standards, IAEA-S1 and IAEA-S3, were carried out at various low concentrations on a dual-inlet isotope ratio mass spectrometer using a microvolume and modified resistor capacities.

Results: The analyses yielded a narrow range of δ(34) S values vs CDT (the international standard), with an overall standard deviation of ±0.2 ‰, which was within the range of certified values. This demonstrates the feasibility of determining both Δ(33) S and Δ(36) S values on the sub-micromole scale, and Δ(33) S values on the nanomole scale with similar accuracy to conventional dual-inlet analyses.

Conclusions: The analysis of the three S-isotope ratios on the SF6 molecule using the so-called conventional fluorination method and dual-inlet ion ratio mass spectrometry is reliable for sample sizes down to ~20 nanomoles. Despite being close to the theoretical limits for maintaining the viscous flow regime of gas in the capillary, errors were not limited by counting statistics, but probably relate to sample gas purification. Copyright © 2016 John Wiley & Sons, Ltd.