EVALUATION OF DITHIOCARBAMATES AND BETA-DIKETONES AS CHELATING-AGENTSIN SUPERCRITICAL-FLUID EXTRACTION OF CD, PB, AND HG FROM SOLID SAMPLES

The use of four dithiocarbamates and three fluorinated beta-diketones as potential chelating agents for three transition metal ions (Cd2+, P b2+, and Hg2+) extracted from spiked sand and filter paper samples by supercritical fluid extraction (SFE) was investigated. The extractions were performed at 45 degrees C and 250 atm for spiked sand samples an d at 60 degrees C and 200 atm for filter paper samples using supercrit ical carbon dioxide modified with 5% methanol. At 250 atm and using ca rbon dioxide modified with 5% methanol, the recoveries of Cd2+, Pb(2+) and Hg2+ ions from spiked sand samples were greater than or equal to 9 5% with lithium bis(trifluoroethyl)dithiocarbamate (LiFDDC) as the che lating agent; they ranged from 83-97% with diethylammonium diethyldith iocarbamate and from 87-97% with sodium diethyldithiocarbamate as chel ating agents, and from 68-96% with trifluoracetylacetone, hexafluoroac etylacetone, and thenoylfluoroacetone as chelating agents. Ammonium py rrolidinedithiocarbamate was not effective in the chelation SFE of Cd2 +, Pb2+, and Hg2+ ions from either spiked sand or spiked filter paper samples under the extraction conditions used. Supercritical carbon dio xide alone gave consistently lower analyte recoveries than supercritic al carbon dioxide modified with 5% methanol. The results suggest that the solubility of the metal chelate in the supercritical fluid plays a more important role than the solubility of the chelating agent in the supercritical fluid, as long as sufficient chelating agent is present in the fluid phase. Fluorination of the chelating agent, as in the ca se of LiFDDC, increases the solubility of the metal chelate, and subse quently enhances the extraction efficiency for the metal ions.