Modified approaches to the complexometric extraction of metal ions into supercritical carbon dioxide

A modified nebulizing assembly from a commercial atomic absorption spectrom etry (AAS) unit served to interface the eluate from a supercritical carbon, dioxide (Sc-CO2) extractor with a flame atomic absorption spectrometer and provided low to sub-ng limits of detection for several elements that were detected only inefficiently with an all-silica T-tube interface. The unit w as used to monitor the progress of complexometric extractions of cobalt and nickel (2.5 or 25 mug/ml) from aqueous medium. Modifications to the genera l process for metal mobilisation included (i) a back-filling procedure duri ng the initial pressurisation of the extractor and (ii.) the separation of the derivatization reaction. from the subsequent extraction. When coupled w ith (iii.) the addition of ethyl acetate or methylisobutyl Ketone to the mo bile phase, residual levels of analyte Co and Ni were reduced to the limit of detection with a single extraction. A heated column of iron granules Fe degrees) efficiently removed metal 2,4-pentanedionate and diethyldithiocarb amate complexes from the SCF extractor eluate but did not liberate any comp lexing reagent. A sea sand column, heated to the same temperature, was less efficient at removing metals but did liberate modest amounts of 2,4-pentan edione back into the mobile phase.