Development of a technique for the analysis of inorganic mercury salts in soils by gas chromatography/mass spectrometry

Abstract

A technique has been developed to analyze environmentally relevant samples for organic and inorganic mercury compounds. A solid phase microextraction (SPME) fiber was used as a sampling medium in both water and water/soil slurries. Quantification of inorganic mercury was accomplished through a chemical alkylation reaction designed to convert an inorganic mercury salt to an organomercury compound prior to GC/MS analysis; this was found to be the rate limiting step in the analysis. Two alkylating reagents were investigated: methylpentacyanocobaltate (III) (K 3[Co(CN) 5CH 3]) and methylbis(dimethylglyoximato)pyridinecobalt (III) (CH 3Co(dmgH) 2Py). Methylbis(dimethylglyoximato)pyridinecobalt (III) was found to be superior for this application because it produced a single reaction product, methylmercury iodide, with an efficiency of ∼95%. Detection limits were ∼7 ppb in water and ∼2 ppm in soil. The poorer results in soil were due to an increase in background signal (∼10 times compared to water) and a reduction in analyte signal (as much as 100 times). This reduction in signal intensity is believed to be caused by complex soil chemistry. Manipulation of the solution chemistry [e.g. oxidation of mercury (0) → mercury (II)], before or during the alkylation step, may improve the detection limits and increase the number of elements amenable to analysis. Keywords: Gas chromatography/mass spectrometry; Inorganic analysis; Elemental; Mercury compounds; Chemical alkylation