Isotope dilution quantification of 200Hg 2+ and CH 3201Hg + enriched species-specific tracers in aquatic systems by cold vapor ICPMS and algebraic de-convoluting

Abstract

The aim of this study was to develop an inductively coupled plasma mass spectrometry (ICPMS) method for the determination of enriched species-specific mercury tracers at ng L −1 levels (ppt) in zooplankton and aquatic samples from biological tracer experiments. Applying a cold vapor sector field ICPMS method a high sensitivity was obtained, i.e., 10 6 cps for 1 μg L −1 of natural mercury measured on 202Hg +, which in turn enabled the measurement of mercury isotope ratios with a 0.6–1.4%R.S.D. precision for a 50 ng L −1 standard. This method was used to quantify CH 3 201Hg + and 200Hg 2+ tracers in zooplankton from a biological tracer experiment with the aim of investigating the effects of algal density and zooplankton density on mercury bioaccumulation in zooplankton in a fresh water system. For quantification purposes a known amount of 199Hg + was added to the zooplankton samples before digestion. The digested samples were analyzed and the resulting ICPMS spectra split into four spectra one for each of the four sources of mercury present in the sample (CH 3 201Hg +, 200Hg 2+, 199Hg 2+ and natural mercury) using algebraic de-convoluting. The CH 3 201Hg + and 200Hg 2+ tracers were quantified using an isotope dilution approach with the added 199Hg +. Detection limits were 0.6 and 0.2 ng L −1 for 200Hg + and CH 3 201Hg +, respectively. The coefficient of variation on the tracer determinations was approximately 18% CV estimated from the analysis of real samples with tracer concentrations in the <0.1–100 ng L −1 range. The developed method was successfully applied for the determination of species-specific mercury tracers in zooplankton samples from a biological tracer experiment.