Near infrared thermal lens spectrometry for the real-time monitoring of supercritical fluid extraction

A commercially available supercritical fluid extractor provided with carbon dioxide was coupled to a dual-beam thermal lens spectrometer with a pumpprobe coaxial configuration, pumped by a pulsed Nd-YAG laser operating at the fundamental wavelength of 1064 nm. As a preliminary step, several compounds were studied in batch regime using carbon tetrachloride as solvent, in order to observe the influence of overtones and combinations involving distinct chemical bonds on thermal lens spectrometry (TLS). Several factors related with supercritical fluid extraction (SFE) under hydrodynamic conditions were studied in order to establish their influence both in the extraction yield and thermal lens signal magnitude obtained. The advantages and limitations of the hyphenated SFE-TLS technique proposed are discussed, and the possibility of on-line detection in SFE with a pulse thermal lens spectrometer was demonstrated.