Carbon dioxide supercritical fluid extraction of incinerator fly ash with a reactive solvent modifier

Abstract

Carbon dioxide supercritical fluid extraction was used to extract polycyclic aromatics, halogenated phenols, halogenated aromatics and dioxins from a municipal incinerator fly ash matrix. The extraction solvent was modified with methanol or a reactive solvent modifier, N,O-bis-trimethylsilyl-trifluoroacetamide (BSTFA), which was added to the sample before extraction. Extracts, obtained at two temperatures and with three supercritical fluid formulations, were analyzed by the US Environmental Protection Agency contract laboratory program GC-MS procedure for semi-volatile organic compounds. Average recoveries of surrogate analytes with pure carbon dioxide and carbon dioxide modified with methanol were 50% (500 atm and 100°C). Average recoveries were 82% at 100°C and 54% at 30°C with BSTFA present. Carbon dioxide modified with methanol was found to be less efficient than carbon dioxide modified with BSTFA. Unlike earlier uses of reactive modifiers, the acidic and phenolic components were determined as the free acids and phenols. Hydrolysis of trimethylsilyl derivatives of phenols, produced by the modifier during the extraction, with methanol reproduced the free phenols. At 60°C the average hydrolysis yield of the four phenols was 96.7%. This hydrolysis step also allowed analysis of free acids by standard methods.