Journal
CHEMICAL GEOLOGY
Volume 304, Issue -, Pages 151-157Publisher
ELSEVIER
DOI: 10.1016/j.chemgeo.2012.02.010
Keywords
Lead isotopes; Pb-depleted; Single collector ICP-MS; Matrix effects; Multiple ion counters; MC-ICP-MS
Categories
Funding
- CFI
- Water Quality Centre
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This work describes an analytical protocol for the measurement of isotope ratios in samples containing small amounts of lead (i.e. <= 0.2 ng total Pb) using the Nu Attom single collector-ICP-MS. The method was evaluated using the NISI' SRM 981 isotopic standard and standard-sample bracketing for correction of the instrumental mass fractionation. The long-term precision (n = 32, +/- 2SD) was 0.11% for the Pb-208/Pb-206 and Pb-207/Pb-206 ratios and 021-0.23% for the Pb-29x/Pb-204 ratios (where x = 208, 207, 206). The precision of the measured Pb isotope ratios reported here (for equivalent total Pb quantities) is comparable to multi-collector (MC) methodologies, using either an array of ion counters (Cocherie and Robert, 2007, Chem. Geol. 243,90-104) or conventional Faraday collectors coupled with a high efficiency sample cone (Makishima and Nakamura, 2010, J. Anal. At. Spectrom. 25, 1712-1716). The accuracy of the measured Pb isotope ratios and the effect of the sample matrix were evaluated for a series of USGS rock standard digests and doped solutions of the NIST SRM 981 standard. For total cation concentrations < 10 mu g mL(-1) and concomitant low concentrations (< 1.5 mu g mL(-1)) of easily ionisable elements (i.e. Na and K), matrix effects were not resolvable at the level of precision reported. However, significant matrix effects were associated with sample compositions typical of natural waters, and removal of (at least) the major cations is required for accurate isotope ratio measurements. (C) 2012 Elsevier B.V. All rights reserved.
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