δ³⁴S Measurements of Sulfur by Multicollector Inductively Coupled Plasma Mass Spectrometry

Abstract

An accurate and precise method for the determination of delta34S measurements by multicollector inductively coupled plasma mass spectrometry has been developed. Full uncertainty budgets, taking into consideration all the uncertainties of the measurement process, have been calculated. The technique was evaluated by comparing measured values with a range of isotopically enriched sulfur solutions prepared by gravimetric addition of a 34S spike. The gravimetric and measured results exhibited a correlation of R2 >0.999. Repeat measurements were also made after adding Na (up to 420 microg g(-1)) and Ca (up to 400 microg g(-1)) salts to the sulfur standard. No significant deviations in the delta34S values were observed. The Russell correction expression (Ingle, C.; Sharp, B.; Horstwood, M.; Parrish, R.; Lewis, D. J. J. Anal. At. Spectrom. 2003, 18, 219) was used to correct for mass bias on the 34S/32S isotope amount ratio from the mass bias observed for the 30Si/28Si isotope amount ratio. Consistent compensation for instrumental mass bias was achieved. Resolution of the measured delta34S values was better than 1 per thousand after consideration of all uncertainty components. The technique was evaluated for practical applications by measurement of delta34S for a range of mineral waters by pneumatic nebulization sample introduction and the analysis of genuine and counterfeit pharmaceuticals using both laser ablation sample introduction and liquid chromatography. For the former two cases polyatomic interferences were resolved by operating the MC-ICPMS in medium resolution, while for the chromatographic analyses polyatomic interferences were minimized by the use of a membrane desolvator, allowing the instrument to be operated at a resolution of 400.

Sulfur isotope measurement of sulfate and sulfide by high-resolution MC-ICP-MS

“…ICP-MS instruments are compatible with numerous sample introduction schemes, including solution (bulk) analysis and laser-ablation (in situ) analysis, which are not available for other techniques. ICP-MS represents a promising technique for the analysis of sulfur isotopes at sample masses (~ 10 µg S) similar to other techniques (Menegário et al, 1998;Mason et al, 1999;Prohaska et al, 1999;Krupp et al, 2004;You and Li, 2005;Clough et al, 2006;Mason et al, 2006). Measurement of S isotopes by single-collector ICP-MS is obtained sequentially and vriability of plasma conditions (e.g., efficiency of ionization, ion beam extraction) can significantly degrade the measurement of isotope ratios.…”

“…The introduction of multiple collector ICP-MS technology has enabled simultaneous measurement of multiple isotopes, providing precise and rapid isotope ratio determination. Precision better than 1 ‰ is now obtainable for δ 34 S isotope ratios (Clough et al, 2006;Mason et al, 2006). Implicit in the accurate and precise determination of isotope ratios by MC-ICP-MS is an appropriate correction for instrumental mass discrimination.…”

“…Implicit in the accurate and precise determination of isotope ratios by MC-ICP-MS is an appropriate correction for instrumental mass discrimination. To date, external normalization (Rehkämper and Halliday, 1998;Maréchal et al, 1999) Si isotope spikes has been preferred for S isotopes studies (Clough et al, 2006;Mason et al, 2006). However, it has not been sufficiently demonstrated that external normalization is appropriate for mass bias correction for all sulfur-bearing samples with a range of matrix, particularly for laser ablation MC-ICP-MS where the matrix cannot be removed prior to analysis.…”

Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA‐ICPMS)

“…Typical applications include age determinations based on parent/daughter decay series such as U/Pb [126], U/Th [127], or Sr isotopes [128]. Other investigations study isotope fractionation by natural processes (e.g., S, Fe, and Os) [16,129,130] or for discriminating sample populations based on the isotope signature of characteristic elements (e.g., Sr in teeth and bones) [131,132].…”

Inductively coupled plasma- and glow discharge plasma-sector field mass spectrometry : Part II. Applications

“…Clough et al demonstrated that the isotopic analysis of S using a MC-ICP-SFMS instrument, operated at higher mass resolution, can be used for distinguishing counterfeit Viagra pills (the active component of which, sildenafil, is a S-containing molecule) from the genuine product. 270 Sample introduction was accomplished via laser ablation and was thus less time-consuming and labour-intensive compared to that required for gas source isotope ratio MS. Also counterfeit products of the antiviral drug Heptodin could be identified on the basis of Mg isotope ratio measurements carried out by MC-ICP-SFMS and complemented by gas source MS data. 271 …”