Mercury speciation analysis in soil samples by ion chromatography, post-column cold vapor generation and inductively coupled plasma mass spectrometry

A method of employing an ion chromatography (IC) column, an online post-column cold vapor (CV) generation system, coupled to an inductively coupled plasma mass spectrometer (ICP-MS), Tor the determination of inorganic mercury (Hg²⁺) and monomethylmercury (CH₃Hg⁺) is described. The IC-CV-ICP-MS technique has generated a method with significant improvements in detection limits as well as shorter analysis time over previous methods. In addition, several major shortcomings associated with the conventional pneumatic nebulization system, e.g., high reflected power from organic solvent introduction into the plasma, deposition of carbon on the sampler and skimmer cones and significant memory effect, have been minimized. The analysis run was finished in as little as six minutes with a mobile phase of 65% methanol and 0.45 M hydrochloric acid. The detection limits (as Hg), based on three times the standard deviation of a standard solution, were found to be 35 pg mL^-1 for Hg²⁺ and 73 pg mL^-1 for CH ₃Hg⁺, with an injection volume of 400 μL. The proposed method was applied to mercury speciation analysis in two soil samples and compared with IC-ICP-MS using conventional pneumatic nebulization for sample introduction. Good agreement was obtained between the two methods. The analysis of extracts from soil samples spiked of Hg²⁺ and CH ₃Hg⁺ with this method showed recoveries of close to 100% for both species.