Aqueous sample preparation for bioassay using supercritical fluid extraction

Abstract

AbstractSupercritical 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 analysis by gas chromatographic or high‐performance liquid chromatographic methods. The objective of this research was to extend SFE applications to aqueous samples extracted on EmporeTM (C18) solid‐phase extraction disks. This technique, which essentially eliminated the use of conventional solvents in preparing the filtered samples, yielded extracts that were compatible with bioassay. The method included aqueous sample extraction onto C18 Empore disks and subsequent elution with supercritical CO2 to isolate and concentrate analytes of interest, using glass beads as an off‐line trapping matrix. Analytes were then redissolved in reconstituted water and evaluated for toxicity using the larval 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 (>90%). Samples of a mixture of these compounds prepared using SFE produced an LC50 of 2.88 mg/L, compared with an LC50 of 2.60 mg/L produced by a water sample directly spiked with equivalent concentrations. Extracts of rice‐field water prepared for bioassay and gas chromatographic analysis using the SFE method gave good recoveries without loss of biological activity.