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We present a direct comparison between two independent methods for the measurement of gaseous elemental mercury (GEM) mass concentration: isotope dilution cold-vapor inductively coupled plasma mass spectrometry (ID-CV-ICP-MS) and laser absorption spectroscopy (LAS). The former technique combined with passive sorbent tube sampling is currently the primary method at NIST for mercury gas standards traceability to the International System of Units (SI). This traceability is achieved via measurements on a mercury-containing reference material. The latter technique has been recently developed at NIST and involves real-time measurements of light attenuation caused by GEM, with SI traceability based in part on the known spontaneous emission lifetime of the probed 6 1S0–6 3P1intercombination transition of elemental mercury (Hg0). Using a steady-flow Hg0-in-air generator to produce samples measured by both methods, we use LAS to measure the sample gas and in parallel we collect the Hg0on sorbent tubes to be subsequently analyzed using ID-CV-ICP-MS. Over the examined mass concentration range (41 μg/m3to 287 μg/m3Hg0in air), the relative disagreement between the two approaches ranged from (1.0 to 1.8)%. The relative combined standard uncertainty on average is 0.4% and 0.9%, for the LAS and MS methods, respectively. Our comparison studies help validate the accuracy of the ID-CV-ICP-MS primary method as well as establish the LAS technique as an attractive alternative primary method for SI-traceable measurements of GEM.

A multi-element quantification strategy based on the method of standard additions incorporating internal standards and collision cell inductively coupled plasma mass spectrometry ICP-MS is presented. Approaches to experimental design are discussed in the context of streamlining analytical measurement protocols employing ratio-based standard additions quantification schemes for the certification of multiple elements in Certified Reference Materials, including reduction of the number of required analytical samples and measurement of analytes and internal standards at alternate quadrupole mass resolution settings. This strategy was implemented for the measurement of As, Se, Fe, Mn, Rb, Cu, and Zn levels in a candidate fish tissue NIST Standard Reference Material and measurement of Cd and Pb in two clinical, whole blood Certified Reference Materials. A simple approach to calculating analytical uncertainties for concentration data, as determined using standard additions calibrations, is presented which utilizes regression and prediction uncertainties and quotient propagation of error formulae.