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

Abstract

Methods for enhancing the extraction efficiency of mercury ion (Hg²⁺) and methylmercury (CH₃Hg⁺) from various solid matrices using a home-made supercritical fluid extraction system combined on-line with atomic absorption spectrometric detection were investigated. The extraction of both spiked Hg²⁺ and CH₃Hg⁺ from various simplified matrices, such as filter-paper, silica gel, aluminium oxide, starch, and cellulose, was achieved with the use of pure and methanol-modified supercritical fluid (CO₂). For Hg²⁺, the effects of different kinds of derivatization and chelating reagents on the extraction efficiency were explored. It was demonstrated that both sodium tetraphenylborate and acetylacetone could be used as derivatization and chelating reagents with high efficiency of extraction from filter-paper using pure supercritical 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⁺ were also assessed. Some attempts were also made to evaluate the extraction behavior of spiked CH₃Hg⁺ and Hg²⁺ in a natural soil sample. According to the effects of extraction pressure and time, the variation of the extraction efficiency of the mercury species of interest was found to be strongly dependent on their adsorption behavior on the sample matrix and the applied extraction parameters. Additionally, it was found that the extraction efficiency of CH₃Hg⁺ could not be improved by using methanol-modified supercritical CO₂. However, the extraction efficiency of Hg²⁺ from soil was significantly elevated from approximately 45 to 80%, if a suitable amount of methanol was used as a modifier.