PULSE THERMAL LENS SPECTROMETRY OF BETA-CAROTENE IN FLOW SYSTEMS AT ATMOSPHERIC-PRESSURE AND HIGH-PRESSURE CONDITIONS

A dual-laser thermal lens spectrometer with a pulse pump-probe coaxial configuration was constructed, optimized, and used to study the influ ence of Bow rate, cell design, nature of the solvent, photostability o f the chromophore, and pressure up to 80 atm. beta-carotene solutions in 2-propanol, n-hexane, and carbon tetrachloride were pumped through a quartz cell (10 mm pathlength, 30 mu L internal volume) and a stainl ess steel cell (50 mm pathlength, 350 mu L internal volume). With beta -carotene, flow produces a relative thermal lens spectrometry (TLS) si gnal magnitude increase owing to replacement of photobleached analyte in the beam region. The effects of pressure in the different solvents are compared and discussed; the relative TLS signal magnitude decrease d when pressure increased, but less in carbon tetrachloride than in th e other solvents. Limit of detection for beta-carotene in carbon tetra chloride at 0.4 mt min(1) and 1 atm were 2 x 10(-5) absorbance units.