Abstract: The thermal-lens apparatus described previously (cf. Dovichi and Harris, Anal. Abstr., 1981, 41, 2J111) was used in conjunction with a microcomputer for real-time data processing. A 1-cm fused-silica flow-cell (1 mm deep) was used in which the carrier stream flowed vertically upwards, thereby minimizing problems due to convection. In the determination of Fe with 1,10-phenanthroline in aqueous methanol (1:1), the limit of detection was 37 pg in a 100 µL sample, while in the determination of azulene and C. I. Solvent Green 3 in CCl4 solution, respective absorbance detection limits of 8.5 x 10^-7 and 14 x 10^-7 were possible. The use of the flow injection procedure was found to minimize problems of photochemical instability frequently encountered in static thermal-lens measurements.

Abstract: The flow system consists of a reservoir of the supercritical fluid (CO2 near its critical point) that is used to fill a high-pressure syringe pump. The fluid is filtered and passed through a reversed-phase ODS chromatographic column (to remove the solvent for the analyte) to a flow cell and back-pressure regulator. The sample (a solution of azulene in hexane) is injected, via a valve, into the flowing supercritical fluid. Detection is by means of a thermal-lens absorption instrument, based on the Kr-ion laser previously described (cf. Anal. Abstr., 1985, 47, 4J100). Use of this technique enhances the sensitivity for azulene (relative to CCl4). Background absorption is low and permits low detection limits.