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Issue 7, 1999
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Determination of sulfur isotope ratios and concentrations in water samples using ICP-MS incorporating hexapole ion optics

Abstract

Sulfur isotope ratios are difficult to determine by quadrupole ICP-MS due to interfering O 2 + and NO + molecular ions of high signal intensity at isotopes 32 S and 34 S. Rf-only hexapole devices have recently been introduced into ICP-MS instrumentation to facilitate ion transfer from interface to analyser. By introducing a mixture of ‘reactive’ gases into the hexapole, a series of ion-molecule reactions can be induced to reduce or remove interfering polyatomic species. The effects of various gas mixtures (He, H 2 and Xe) on the transfer of sulfur ions through the hexapole and the breakdown of interfering O 2 + and NO + molecular ions at m/z=32 and m/z=34 were investigated. A rapid charge transfer reaction between O 2 + and Xe gives at least a factor of 10 improvement in the S + /O 2 + ratio. A further reduction in O 2 + is achieved by the addition of H 2 . δ 34 S variations were investigated in crater-lake waters and waters obtained from springs and rivers on the flanks of volcanoes in Java, Indonesia. Under optimum conditions (S=10-50 mg l –1 ), the 34 S/ 32 S measurement precision for standards and samples was <0.3% RSD. Mass bias errors were corrected by using a concentration-matched in-house standard of average North Atlantic sea-water (δ 34 S=20.5). Results compare favorably against published data measured by standard gas source mass spectrometric techniques. The proposed technique is potentially useful as a survey tool due to the large δ 34 S variation (±20) encountered in nature and the accuracy and reproducibility of the technique (±3-5).

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Article information


J. Anal. At. Spectrom., 1999,14, 1067-1074
Article type
Paper

Determination of sulfur isotope ratios and concentrations in water samples using ICP-MS incorporating hexapole ion optics

P. R. D. Mason, K. Kaspers and M. J. van Bergen, J. Anal. At. Spectrom., 1999, 14, 1067
DOI: 10.1039/A902037C

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