MERCURY ISOTOPES DETERMINATIONS IN ENVIRONMENTAL SAMPLES BY MULTICOLLECTOR ICP/MS

Mercury isotopes can be an effective tool to investigate about the biogeochemical cycle of Hg, in order to distinguish among different sources and prevent its well-known pollution in environment and food webs. In this work, we set up a method for Hg isotopic ratio determination by multicollector ICP-MS spectrometry by using a cold vapour generator system (CVG). Basically, the system permits to get measures independent from any matrix effects achieving high precisions and sensitivities. The method was optimized by Design of Experiment (DoE) technique to minimize inner uncertainty on isotopic ratios. Instrumental mass bias on measures was accounted by simultaneously monitoring 205Tl/203Tl from the isotopic SRM NIST 997 and applying the correction algorithm proposed by Yang and Sturgeon. The method repeatability and reproducibility were evaluated for a two years period on a large data set built by measuring the NIST 3133 standard solution with an Hg concentration of 20 ng g-1 for more than 500 times. Hg isotope ratios (expressed as mean ± 2 standard deviations), are comparable with those of others works for all the monitored species, namely 199Hg/198Hg = 1.6881 ± 0.0006, 200Hg/198Hg = 2.3061 ± 0.0011, 201Hg/198Hg = 1.3139 ± 0.0014 and 202Hg/198Hg = 2.9635 ± 0.0014. Precisions and sensitivities of the method are fit for purpose to investigate fractionation phenomena, mass dependent (MDF) and mass independent (MIF), for Hg that might occur during the uptake processes of the element and its derivatives in living organisms.