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

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)(5)CH3]) and methylbis(dimethylglyoximato)pyridinecobalt (III) (CH3Co(dmgH(2)Py). 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 similar to 95%. Detection limits were similar to 7 ppb in water and similar to 2 ppm in soil. The poorer results in soil were due to an increase in background signal (similar to 10 times compared to water) and a reduction in analyte signal las 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. (Int J Mass Spectrom 178 (1998) 31-41) (C) 1998 Elsevier Science B.V.