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Issue 9, 2003
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Uncertainty contributions to species specific isotope dilution analysis. Part 2. Determination of methylmercury by HPLC coupled with quadrupole and multicollector ICP-MS

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Abstract

Species-specific isotope dilution analysis (IDA) has been used to determine the mass fraction of methylmercury in a fish muscle certified reference material, DORM-2. Two spike solutions were prepared and their mass fractions determined by coupling high-performance liquid chromatography (HPLC) with both quadrupole (Q) and multicollector (MC) inductively coupled plasma mass spectrometry (ICP-MS) and uncertainty budgets calculated. For the Q-ICP-MS determination the relative standard uncertainty of the spike was 4.1%. The major uncertainty contribution (62%) arose from the uncertainties associated with the relative isotopic abundances of Hg isotopes as given by IUPAC. The measured isotope amount ratios (200Hg∶199Hg and 205Tl∶203Tl) contributed 37% of the combined uncertainty. For the multicollector instrument the relative standard uncertainty of the spike solution mass fraction was 0.7%. In this case the uncertainty budget was dominated by the Hg isotopic uncertainties, with a contribution of 99%. The uncertainty contributions from the measured isotope amount ratios were reduced to 0.7% of the total when using MC-ICP-MS. The two spike solutions were separately used to determine the mass fraction of methylmercury in DORM-2 CRM by species-specific IDA, using HPLC coupled with quadrupole ICP-MS. The values found were 4.45 ± 0.90 µg g−1 and 4.25 ± 0.47 µg g−1 using spikes characterised by Q- and MC-ICP-MS, respectively (the uncertainties quoted are the expanded uncertainty, k = 2), compared with a certified value of 4.47 ± 0.32. The major uncertainty contribution for each determination was from the measured isotope amount ratios (70%) with lesser contributions from the uncertainties associated with the natural isotopic abundance of Hg and the spike mass fraction.

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Publication details

The article was received on 12 Mar 2003, accepted on 16 May 2003 and first published on 09 Jul 2003


Article type: Paper
DOI: 10.1039/B305454N
Citation: J. Anal. At. Spectrom., 2003,18, 1039-1046
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    Uncertainty contributions to species specific isotope dilution analysis. Part 2. Determination of methylmercury by HPLC coupled with quadrupole and multicollector ICP-MS

    R. Clough, Simon. T. Belt, E. H. Evans, B. Fairman and T. Catterick, J. Anal. At. Spectrom., 2003, 18, 1039
    DOI: 10.1039/B305454N

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