Stability of Organic Pollutants during Microwave-Assisted Extraction from Solid Matrixes

Abstract

A stability study was conducted for 95 semivolatile organics listed in U.S. Environmental Protection Agency Method 8250 (this number includes 6 surrogate compounds). These compounds were spiked into solvent only [hexane-acetone (1 + 1), methylene chloride-acetone (1 + 1), toluene-methanol (10 + 1), and methyl fert-butyl ether], solvent/dry soil suspensions, and solvent/wet soil suspensions [20% water (w/w)] and heated with microwave energy in closed vessels at 50° or 145°C for 5 or 20 min. For comparison and to determine nitrogen blowdown losses, spiked solvent samples that had not been exposed to microwave energy were concentrated by the blowdown technique and analyzed for each of the spiked compounds. Hexane-acetone (1 + 1) seems to be the best for the compounds and matrixes investigated, with recoveries >80%, except for basic compounds and benzoic acid in the solvent/dry soil suspension experiments. Increasing extraction time from 5 to 20 min did not increase recoveries; in fact, recoveries of neutral compounds decreased slightly at the longer extraction time. Increasing the temperature from 50° to 145°C decreased recoveries of basic compounds by about 10%. Recoveries of basic compounds, of benzoic acid (and probably other organic acids as well), and at least to some extent of phenolic compounds from the solvent/wet soil suspensions were higher than those for solvent/dry soil suspensions.