CARBON-DIOXIDE SUPERCRITICAL-FLUID EXTRACTION OF INCINERATOR FLY-ASH WITH A REACTIVE SOLVENT MODIFIER

Carbon dioxide supercritical fluid extraction was used to extract poly cyclic aromatics, halogenated phenols, halogenated aromatics and dioxi ns from a municipal incinerator fly ash matrix. The extraction solvent was modified with methanol or a reactive solvent modifier, N,O-bis-tr imethylsilyl-trifluoroacetamide (BSTFA), which was added to the sample before extraction. Extracts, obtained at two temperatures and with th ree supercritical fluid formulations, were analyzed by the US Environm ental Protection Agency contract-laboratory program GC-MS procedure fo r semi-volatile organic compounds. Average recoveries of surrogate ana lytes with pure carbon dioxide and carbon dioxide modified with methan ol were 50% (500 atm and 100 degrees C). Average recoveries were 82% a t 100 degrees C and 54% at 30 degrees C with BSTFA present. Carbon dio xide modified with methanol was found to be less efficient than carbon dioxide modified with BSTFA. Unlike earlier uses of reactive modifier s, the acidic and phenolic components were determined as the free acid s and phenols. Hydrolysis of trimethylsilyl derivatives of phenols, pr oduced by the modifier during the extraction, with methanol reproduced the free phenols. At 60 degrees C the average hydrolysis yield of the four phenols was 96.7%. This hydrolysis step also allowed analysis of free acids by standard methods.