Pulse Thermal Lens Spectrometry of β-Carotene in Flow Systems at Atmospheric- and High-Pressure Conditions

Abstract

A dual-laser thermal lens spectrometer with a pulse pump-probe coaxial configuration was constructed, optimized, and used to study the influence of flow rate, cell design, nature of the solvent, photostability of the chromophore, and pressure up to 80 atm. β-carotene solutions in 2-propanol, n-hexane, and carbon tetrachloride were pumped through a quartz cell (10 mm pathlength, 30 μL internal volume) and a stainless steel cell (50 mm pathlength, 350 μL internal volume). With β-carotene, flow produces a relative thermal lens spectrometry (TLS) signal 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 decreased when pressure increased, but less in carbon tetrachloride than in the other solvents. Limit of detection for β-carotene in carbon tetrachloride at 0.4 mL min-¹ and 1 atm were 2 × 10-⁵ absorbance units.