The solubility of a tert-butyl-substituted dibenzobistria-zolo-crown ether in methanol (5 mol %) modified CO_2 has been determined to be in the order of 1 x 10~(-3) M at 60℃ and 200 atm. Using this proton-ionizable crown ether as an extractant in methanol (5%) modified CO_2, quantitative extraction of Hg~(2+) from sand and cellulose-based filter papers can be achieved at 60℃ and 200 atm if a small amount of water is present in the solid matrix. Other divalent metal ions including Cd~(2+), Co~(2+), Mn~(2+), Ni~(2+), Pb~(2+), and Zn~(2+) are virtually not extractable under these conditions. Gold (Au~(3+)) can be extracted by the macro-cyclic ligand with a lower efficiency than Hg~(2+). Extraction of Hg~(2+) from aqueous samples can also be achieved using methanol-modified CO_2 containing the macrocyclic ligand. formation of extractable metal chelates with the ligand at the pH defined by the CO_2-H_2O system appears to be an important factor determining the extraction efficiencies of the metal ions by this in situ chelation-supercritical fluid extraction technique.
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