Monitoring supercritical fluid extraction by thermal lens spectrometry with pulsed laser excitation

A dual-beam thermal lens spectrometer (TLS) with a pulse pump-probe coaxial configuration was coupled to commercially available supercritical fluid extraction equipment using a high-pressure flow cell interface. Because of its feasible critical parameters, moderate cost and good thermooptical properties, carbon dioxide was used as supercritical solvent. Using trans-beta-carotene as analyte, several factors related with the extraction process under continuos flow conditions were studied in order to establish their influence in the thermal lens signal magnitude. Under the optimum experimental conditions, the relative TLS signal area showed a linear relationship with the concentration of trans-beta-carotene from 1.5x10(-6) to 8x10(-8) M (n=5, r=0.998) in the supercritical phase. Thus, the viability of on-line detection for supercritical fluid extraction with a pulse thermal lens spectrometer was demonstrated. (C) 1999 Elsevier Science B.V. All rights reserved.