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 hydrocarbons (PAHs) ranging from naphthalene (M = 128) to benzo[b]fluoranthene (M = 252) and those of spiked deuterated PAHs (d-PAHs) from heterogeneous environmental samples including petroleum waste sludge, urban air particulate matter (SRM 1649), and railroad bed soil were compared using sequential extractions with pure supercritical CO2 or modified (10% v/v methanol) supercritical CO2 and using sonication with methylene chloride. Regardless of the spiking method (injection of the spike or suspension of the sample in the spiking solution) or aging time (up to 14 h), the extraction rates of most of the spiked d-PAHs were substantially (up to 10-fold) higher than those of the same native PAHs. Differences in extraction rates of the spiked and native PAHs were most dramatic for the lower molecular weight PAHs, indicating that relatively volatile species such as naphthalene must be tightly bound in order to remain associated with a real-world sample. In most cases, 30-min extractions with pure CO2 quantitatively recovered (>90%) the spiked deuterated-PAHs, but only extracted ca. 25-80% of the native PAHs. Similar differences were observed using conventional methylene chloride sonication, demonstrating that spike recovery studies are not valid for developing quantitative extraction methods for heterogeneous environmental samples.