RAPID-DETERMINATION OF INORGANIC MERCURY AND METHYLMERCURY IN BIOLOGICAL REFERENCE MATERIALS BY HYDRIDE GENERATION, CRYOFOCUSING, ATOMIC-ABSORPTION SPECTROMETRY AFTER OPEN FOCUSED MICROWAVE-ASSISTED ALKALINE DIGESTION

A rapid and simple microwave-assisted digestion method with alkaline s olution (tetramethylammoniom hydroxide or methanolic KOH solution) for speciation analysis of inorganic mercury and methylmercury (MeHg+) in biological tissues was developed. Extracts with quantitative recoveri es of mercury species after microwave-assisted alkaline dissolution of the sample were directly analysed by an automated on-line hyphenated system incorporating aqueous hydride generation, cryogenic trapping, g as chromatography and detection by atomic absorption spectrometry. Opt imum conditions allow sample throughput to be controlled by the instru mental analysis time (approximate to 10 min per sample) and not by the sample preparation step. At a power of 40-60 W, sample preparation ti me is only 2-4 min, which is much faster than previous literature meth ods. The proposed method was validated by the analysis of three biolog ical certified reference materials, CRM 463, DORM-1 and TORT-1, and on e BCR sample from an interlaboratory study, Tuna Fish 2. The detection limit of the overall procedure was found to be 3 ng per gram of pulve rised dried biological tissue, for both labile Hg2+ and MeHg+. After a lkaline extraction, a mean recovery of 102% with a relative standard d eviation of 7% was obtained for methylmercury concentrations ranging f rom 0.128 to 3.464 mu g g(-1) as Hg in the four reference fish tissues mentioned above. Total mercury, calculated as the sum of determined i norganic mercury and methylmercury, was also in agreement with the cer tified values. The methylmercury extraction efficiency of five extract ants, viz., nitric, hydrochloric and acetic acid, and tetramethylammon ium hydroxide and methanolic KOH solution, the temperature profile of- these extractants under microwave irradiation and the behaviour and st ability of methylmercury in a focused microwave field were also invest igated.