Selective extraction of mercury with ionizable crown ethers in supercritical carbon dioxide

Abstract

The solubility of a ferf-butyl-substituted dibenzobistriazolo-crown ether in methanol (5 mol %) modified CO2 has been determined to be in the order of 1 x 10"1 23 M at 60 °C and 200 atm. Using this proton-ionizable crown ether as an extractant in methanol (5%) modified CO2, quantitative extraction ofHg2 5" from sand and cellulose-based filter papers can be achieved at 60 °C and 200 atm if a small amount of water is present in the solid matrix. Other divalent metal ions including Cd2+, Co2+, Mn2+, Ni2+, Pb2+, and Zn2+ are virtually not extractable imder these conditions. Gold (Au3+) can be extracted by the macrocyclic ligand with a lower efficiency than Hg2+. Extraction of Hg2+ from aqueous samples can also be achieved using methanol-modified CO2 containing the macrocyclic ligand.Formation of extractable metal chelates with the ligand at the pH defined by the CO2-H2O system appears to be an important factor determining the extraction efficiencies of the metal ions by this in situ chelation-supercritical fluid extraction technique. Supercritical fluid extraction (SFE) of metal species from solid and liquid materials has been the subject of several recent studies.1-5 One approach for extracting metal ions in supercritical CO2 is to convert the charged metal species into neutral metal chelates by use of a suitable ligand dissolved in the fluid phase. This in situ chelation-SFE method has been shown to exhibit high efficiencies for extracting metal ions from solid and liquid materials when a fluorinated chelating agent such as lithium bis-(trifluoroethyl) dithiocarbamate (IiFDDC) or a fluorinated /3-diketone is used as an extractant in supercritical CO2.1,2,4 It is conceivable that selective extraction of metal ions in supercritical fluids may be achieved if the chelating agent possesses an ion recognition capability.Dithiocarbamate and /3-diketones are not selective chelating agents because they complex with a large number of metals and non-metals. These chelating agents are also difficult to regenerate because of their instability in acid solutions. Crown ethers are a class of selective ligands that form stable complexes with metal ions based primarily on the ionic radius-cavity size compatibility concept.6 Modification of crown structure by attaching negatively

Fast separation of triterpenoid saponins using supercritical fluid chromatography coupled with single quadrupole mass spectrometry

“…2 also shows that the highest detection sensitivity was obtained with a water content of 8%. Water in contact with scCO 2 becomes acidic due to the formation and dissociation of carbonic acid [30], and its ability to function both as a hydrogen bond acceptor and a hydrogen bond donor has been recognized to enhance its role as an additive in SFC [31]. However, it is worth noting that both resolution and peak shape were found to worsen with a further increase of the water content to 12%.…”

Metal Ion Extraction with Bipyridine Derivatives as Chelating Ligands in Supercritical Carbon Dioxide

“…However, when metal ions are bound to organic ligands and form neutral species, their solubilities in sc-CO2 can be significantly increased [4][5][6][7][8]. To date, many chelating ligands have been used to extract metal ions in sc-CO 2 , e. g., crown ethers, b-diketones, dithiocarbamates, phosphates, and amines [9][10][11][12][13].…”

Supercritical CO2extraction of porogen phase: An alternative route to nanoporous dielectrics

“…9 In a previous paper, we reported the ability of SCCO 2 to dissolve low molecular weight and loosely bonded species in films prepared by plasma-enhanced CVD. 10 Supercritical CO 2 has been used effectively for the extraction and isolation of organic and inorganic compounds, including removal of hazardous organic waste from contaminated soil, 11,12 fractionation of natural oils, [13][14][15][16] and extraction of biomolecules, 17 metal ions, [18][19][20][21] and polymerization catalysts. 22 We believe that extraction of porogens in a hybrid inorganic-organic film for semiconductor applications is unique and applied for the first time by our group.…”