Determination of Metals in Solid Samples by Complexation--Supercritical Fluid Extraction and Gas Chromatography--Atomic Emission Detection

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Abstract
Complexation followed by supercritical fluid extraction (SFE) has been investigated for the extraction of Cu2+, Co2+, Cd2+, and Zn2+ ions from solid samples. Lithium bis(trifluoroethyl)dithiocarbamate (FDDC) was used as the complexing agent in this study. The metal-FDDC complexes in the SFE extracts were determined by gas chromatography with atomic emission detection. The recoveries of Cu2+, Co2+, Cd2+, and Zn2+ ions from filter paper, sand, and silica gel (spiked at 10 µg/strip of filter paper or 10 µg/g sand or silica gel) ranged from about 70 to 100%. Relatively high concentrations of complexed Cu, Co, Cd, and Zn found in system blanks obtained with a stainless steel SFE system prompted us to modify the apparatus by using nonmetallic polyetheretherketone (PEEK) components. Levels of these metals in system blanks generated using the modified system were only 10 to 30% of those generated using the stainless steel system. The techniques for the addition of the solid or dissolved complexing agent to the samples are discussed. This new approach to the extraction and determination of inorganic ions from solid samples, if generally applicable, could result in significant reductions in the use of organic solvents and acids specified in conventional extraction methods.

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