Supercritical Fluid Carbon Dioxide Extraction and Liquid Chromatographic Separation with Electrochemical Detection of Methylmercury from Biological Samples

Abstract

Using the coupled methods presented in this paper, methylmercury can be accurately and rapidly extracted from biological samples by modified supercritical fluid carbon dioxide and quantitated using liquid chromatography with reductive electrochemical detection. Supercritical fluid carbon dioxide modified with methanol effectively extracts underivatized methylmercury from certified reference materials Dorm-1 (dogfish muscle) and Dolt-2 (dogfish liver). Calcium chloride and water, with a ratio of 5:2 (by weight), provide the acid environment required for extracting methylmercury from sample matrices. Methylmercury chloride is separated from other organomercury chloride compounds using HPLC. The acidic eluent, containing 0.06 mol L^–1 NaCl, insures the presence of methylmercury chloride and facilitates the reduction of mercury on a glassy carbon electrode. If dual glassy carbon electrodes are used, a positive peak is observed at –0.65 to –0.70 V and a negative peak is observed at –0.90V with the organomercury compounds that were tested. The practical detection limit for methylmercury is 5 × 10^–8 mol L^–1 (1 × 10^–12 mol injected) when a 20 μL injection loop is used.

Key Words:

• Methylmercury
• supercritical fluid extraction (SFE)
• liquid chromatography
• electrochemical detection
• biological samples