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An isotope dilution cold vapor inductively coupled plasma mass spectrometry (ID-CV-ICPMS) method featuring gaseous introduction of mercury via tin chloride reduction has been developed and applied to the quantification and certification of mercury in various NIST standard reference materials: SRM 966 Toxic Metals in Bovine Blood (30 ng x mL(-1)); SRM 1641d Mercury in Water (1.6 microg x mL(-1)); and SRM 1946 Lake Superior Fish Tissue (436 ng x g(-1)). Complementary mercury data were generated for SRMs and NIST quality control standards using cold vapor atomic absorption spectroscopy (CVAAS). Certification results for the determination of mercury in SRM 1641d using two independent methods (ID-CV-ICPMS and CVAAS) showed a degree of agreement of 0.3% between the methods. Gaseous introduction of mercury into the ICPMS resulted in a single isotope sensitivity of 2 x 10(6) counts x s(-1)/ng x g(-1) for 201Hg and significantly reduced the memory and washout effects traditionally encountered in solution nebulization ICPMS. Figures of merit for isotope ratio accuracy and precision were evaluated at dwell times of 10, 20, 40, 80, and 160 ms using SRM 3133 Mercury Spectrometric Solution. The optimum dwell time of 80 ms yielded a measured 201Hg/202Hg isotope ratio within 0.13% of the theoretical natural value and a measurement precision of 0.34%, on the basis of three replicate injections of SRM 3133.

The Comité Consultatif pour la Quantité de Matière (CCQM) endeavours to identify and carry out key activities with the objective of facilitating world-wide comparability and traceability of chemical measurements. Towards this goal, the CCQM has identified comparisons to be carried out using candidate primary methods of chemical analysis. One such method is isotope dilution mass spectrometry. In the first comparison carried out by the CCQM (Study I), the concentrations of various inorganic elements were determined in water solutions using IDMS. The results did not meet the target level of 1% maximum relative deviation from the reference values of the unknowns. It was concluded that more guidance was necessary on the execution of the IDMS method and that a detailed protocol should be developed. Participants would use inductively coupled plasma (ICP) as the ionization source. Here we present the protocol developed for use by CCQM participants in the next comparison (Study III) on the determination of the concentration of lead in water using the IDMS method with an inductively coupled plasma-mass spectrometer.