STABILITY OF ORGANIC POLLUTANTS DURING MICROWAVE-ASSISTED EXTRACTION FROM SOLID MATRICES

A stability study was conducted for 95 semivolatile organics listed in U.S. Environmental Protection Agency Method 8250 (this number include s 6 surrogate compounds). These compounds were spiked into solvent onl y [hexane-acetone (1 + 1), methylene chloride-acetone (1 + 1), toluene -methanol (10 + 1), and methyl tert-butyl ether], solvent/dry soil sus pensions, and solvent/wet soil suspensions [20% water (w/w)] and heate d with microwave energy in closed vessels at 50 degrees or 145 degrees 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 ea ch of the spiked compounds. Hexane-acetone (1 + 1) seems to be the bes t for the compounds and matrixes investigated, with recoveries > 80%, except for basic compounds and benzoic acid in the solvent/dry soil su spension experiments. Increasing extraction time from 5 to 20 min did not increase recoveries; in fact, recoveries of neutral compounds decr eased slightly at the longer extraction time. Increasing the temperatu re from 50 degrees to 145 degrees C decreased recoveries of basic comp ounds by about 10%. Recoveries of basic compounds, of benzoic acid (an d probably other organic acids as well), and at least to some extent o f phenolic compounds from the solvent/wet soil suspensions were higher than those for solvent/dry soil suspensions.