Study of matrix influence on supercritical fluid extraction of polar mercury species from solid samples

Methods for enhancing the extraction efficiency of mercury ion (Hg2+) and m ethylmercury (CH3Hg+) front various solid matrices using a home-made superc ritical fluid extraction system combined on-line with atomic absorption spe ctrometric detection were investigated. The extraction of both spiked Hg2and CH3Hg+ from various simplified matrices, such as filter-paper, silica g el, aluminium oxide, starch, and cellulose, was achieved with the use of pu re and methanol-modified supercritical fluid (CO2). For Hg2+, the effects o f different kinds of derivatization and chelating reagents on the extractio n efficiency were explored. It was demonstrated that both sodium tetrapheny lborate and acetylacetone could be used as derivatization and chelating rea gents with high efficiency of extraction from filter-paper using pure super critical CO2. The effects of material (soil) particle size and a variety of organic substances such as humic acid, ethylenediaminetetraacetic acid and ammonium pyrrolidinedithiocarbamate on the extraction of Hg2+ or CH3Hg+ we re also assessed. Sonic attempts were also made to evaluate the extraction behavior of spiked CH3Hg+ and Hg2+ in a natural soil sample. According to t he effects of extraction pressure and time, the variation of the extraction efficiency of the mercury species of interest was found to be strongly dep endent on their adsorption behavior on the sample matrix and the applied ex traction parameters. Additionally, it was found that the extraction efficie ncy of CH3Hg+ could not be improved by using methanol-modified supercritica l CO, However, the extraction efficiency of Hg2+ from soil was significantl y elevated from approximately 45 to 80%, if a suitable amount of methanol w as used as a modifier.