EXTRACTION RATES OF SPIKED VERSUS NATIVE PAHS FROM HETEROGENEOUS ENVIRONMENTAL-SAMPLES USING SUPERCRITICAL-FLUID EXTRACTION AND SONICATION IN METHYLENE-CHLORIDE

The relative extraction rates of native polycyclic aromatic hydrocarbo ns (PAHs) ranging from naphthalene (M = 128) to benzo[b]fluoranthene ( M = 252) and those of spiked deuterated PAHs (d-PAHs) from heterogeneo us environmental samples including petroleum waste sludge, urban air p articulate matter (SRM 1649), and railroad bed soil were compared usin g sequential extractions with pure supercritical CO2 or modified (10% v/v methanol) supercritical CO2 and using sonication with methylene ch loride. Regardless of the spiking method (injection of the spike or su spension of the sample in the spiking solution) or aging time (up to 1 4 h), the extraction rates of most of the spiked d-PAHs were substanti ally (up to 10-fold) higher than those of the same native PAHs. Differ ences in extraction rates of the spiked and native PAHs were most dram atic for the lower molecular weight PAHs, indicating that relatively v olatile species such as naphthalene must be tightly bound in order to remain associated with a real-world sample. In most cases, 30-min extr actions with pure CO2 quantitatively recovered (>90%) the spiked deute rated-PAHs, but only extracted ca. 25-80% of the native PAHs. Similar differences were observed using conventional methylene chloride sonica tion, demonstrating that spike recovery studies are not valid for deve loping quantitative extraction methods for heterogeneous environmental samples.