Supercritical fluid extraction of ionic alkyllead species from sediment and urban dust

Abstract

A method for the supercritical fluid extraction of ionic alkyllead species from solid samples has been developed. Preliminary experiments indicated that methanol was a superior modifier in comparison to water and acetone in supercritical carbon dioxide (added as solutions corresponding to 10% of the extraction cell volume), and it was used in all subsequent work. Following collection in methanol, the ionic alkylleads were extracted as diethyldithiocarbamate complexes into hexane, propylated using a Grignard reagent, and quantified using gas chromatography–mass spectrometry. Optimization of the extraction temperature and pressure was performed using response surface methodology, yielding recoveries of 96, 106 and 80% for trimethyllead, triethyllead and diethyllead, respectively, from spiked sediment samples under optimal conditions (temperature, 80 °C, pressure, 45 MPa). To demonstrate the validity of the method, an urban dust sample distributed by the European Communities Measurements and Testing Programme as part of an intercalibration exercise was analysed using the developed procedure. The concentration of trimethyllead obtained, 6.6 ± 0.5 ng g^–1( expressed as trimethyllead) was in agreement with the mean value from the intercalibration study (6.6 ± 1.3 ng g^–1).