AQUEOUS SAMPLE PREPARATION FOR BIOASSAY USING SUPERCRITICAL-FLUID EXTRACTION

Supercritical fluid extraction (SFE) has become a valuable tool in the preparation of environmental samples for analysis. Most applications to date have been to extract compounds from solid matrices for later a nalysis by gas chromatographic or high-performance liquid chromatograp hic methods. The objective of this research was to extend SFE applicat ions to aqueous samples extracted on Empore(TM) (C-18) solid-phase ext raction disks. This technique, which essentially eliminated the use of conventional solvents in preparing the filtered samples, yielded extr acts that were compatible with bioassay. The method included aqueous s ample extraction onto C-18 Empore disks and subsequent elution with su percritical CO2 to isolate and concentrate analytes of interest, using glass beads as an off-line trapping matrix. Analytes were then rediss olved in reconstituted water and evaluated for toxicity using the larv al medaka, Oryzias latipes, 96-h static toxicity bioassay. Tests with water spikes of molinate, thiobencarb, methyl parathion, and malathion extracted on disks and eluted by SFE gave quantitative recoveries (>9 0%). Samples of a mixture of these compounds prepared using SFE produc ed an LC50 of 2.88 mg/L, compared with an LC50 of 2.60 mg/L produced b y a water sample directly spiked with equivalent concentrations. Extra cts of rice-field water prepared for bioassay and gas chromatographic analysis using the SFE method gave good recoveries without loss of bio logical activity.