Using thermal analysis coupled to isotope dilution cold vapor ICP-MS in the quantification of atmospheric particulate phase mercury

Abstract

An analytical method combining thermal analysis with isotope dilution cold vapor inductively coupled plasma mass spectrometry, ID-CV-ICP-MS, was developed to study mercury in particulate matter samples collected in urban Detroit, MI. We used this method to quantify mercury in NIST 1633b “mercury in fly ash standard” and determined an average concentration of 0.139 ± 0.009 μg g−1 (RSD 6%), which was within the certified range of 0.141 ± 0.019 μg g−1 determined by the National Institute of Standards and Technology using cold vapor atomic absorption spectrometry. The method detection limit for each 3 second integration window was approximately 20 fg of mercury. When we compared results from thermal analysis coupled to ID-CV-ICP-MS to a well-established analysis method that combines microwave assisted nitric acid digestion with cold vapor atomic fluorescence spectroscopy, mercury concentrations were found to be in good agreement with each other indicating that the former is a suitable technique for quantitative release and analysis of mercury from aerosol matrices. Using this method mercury concentrations in denuded and undenuded fine particulate samples collected in Detroit, MI were quantified. Undenuded filters collected more particulate mercury compared to filters that were denuded using a KCl-coated denuder in 60% of samples. Thermal profiles for samples revealed complex patterns and differences in amounts and release patterns of mercury likely due to temporal differences in meteorology and air shed properties that were evident during sampling. Night time samples that were undenuded revealed the most complexity and may be a reflection of increased partitioning of reactive gaseous mercury to the particle phase with decreasing overnight temperatures and reduced height of the boundary layer. These profiles suggest that binding sites of varying physical and chemical characteristics in particulate matter are available for sorption and/or condensation of reactive gaseous mercury.