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Issue 8, 2009
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High-precision cadmium stable isotope measurements by double spike thermal ionisation mass spectrometry

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Abstract

Natural mass-dependent fractionation (MDF) of cadmium isotopes is a promising new tool for investigating Cd pathways and cycling in geological and biological materials. One interesting new application is as chemical tracer of deep water circulation and nutrient distribution in the oceans. But since natural isotope fractionation of Cd appears to be extremely limited and Cd abundances low, excellent external precision and sensitivity are needed to make full use of its potential. Here, we describe a newly-developed double spike (DS) method for determining the MDF of Cd isotopes. For inorganic matrices, samples are spiked with a mixed 106Cd-108Cd tracer prior to high-purity anion exchange-based separation of Cd. Isotope measurements are performed by TIMS using a silica gel activator. Overall, the DS-TIMS technique offers benefits in terms of superior precision and sensitivity compared to MC-ICPMS methods currently in use. External precisions on 100-ng-sized Cd standard loads, double spiked as unknowns, are ±14 ppm on the 112Cd/110Cd ratio (2SD), while ionization efficiencies (ions per atom loaded) are ∼0.3%. Using this technique, we calibrated the relative difference in MDF between several Cd standard materials used in various laboratories as “zero reference standards”. We also show that the 112Cd/110Cd ratio can be fractionated by as much as ∼0.2% by ion-exchange elution, which is potentially problematic for Cd isotope studies not using a double spike.

Graphical abstract: High-precision cadmium stable isotope measurements by double spike thermal ionisation mass spectrometry

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Publication details

The article was received on 05 Dec 2008, accepted on 28 Apr 2009 and first published on 26 May 2009


Article type: Paper
DOI: 10.1039/B821576F
Citation: J. Anal. At. Spectrom., 2009,24, 1079-1088
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    High-precision cadmium stable isotope measurements by double spike thermal ionisation mass spectrometry

    A. Schmitt, S. J. G. Galer and W. Abouchami, J. Anal. At. Spectrom., 2009, 24, 1079
    DOI: 10.1039/B821576F

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