ROLE OF MODIFIERS FOR ANALYTICAL-SCALE SUPERCRITICAL-FLUID EXTRACTIONOF ENVIRONMENTAL-SAMPLES

Supercritical fluid extraction (SFE) using eight different CO2 + organ ic modifier mixtures and one ternary mixture (CO2 + methanol/toluene) at two different concentrations (1 and 10% v/v) was performed on two c ertified reference materials including polychlorinated biphenyls (PCBs ) from river sediment and dolycyclic aromatic hydrocarbons (PAHs) from urban air particulate matter. The modifier identity was moire importa nt than modifier concentration for increasing extraction efficiencies. Acidic/basic modifiers including methanol, acetic acid, and aniline g reatly enhanced the extraction of PCBs. Low molecular weight PAHs were best extracted with modifiers including aniline, acetic acid, acetoni trile, methanol/toluene, hexane, and diethylamine. In contrast, modifi ers capable of dipole-induced dipole interactions and pi-pi interactio ns such as toluene, diethylamine, and methylene chloride were the best modifiers to use for SFE of high molecular weight PAHs from air parti culates. In general, increasing the modifier concentration from 1 to 1 0% (v/v) had little effect on PCB and low molecular weight PAH recover ies, although the recoveries of high molecular weight PAHs from urban air particulate matter were enhanced significantly at the higher modif ier concentration. Although there is no definite theory that explains modifier selection for SFE, it appears that modifiers should be select ed on the basis of matrix characteristics and the target analytes.