ABSTRACT
The introduction of hyphenated techniques in thin-layer chromatography (TLC) was a substantial step forward for the detection/identi cation and quanti cation of compounds from very complex mixtures. Identi cation and quanti cation of unknown compounds from a mixture is one of the fundamental problems in analytical chemistry. It is well known that TLC provides insuf cient information to obtain a reliable identi cation of the compound using only retention values. This problem has been solved due to the remarkable progress made in the last two decades by coupling TLC with other detection methods such as ultraviolet/visible (UV/Vis) spectrometry, uorescence spectrometry (FS), infrared spectrometry (IRS), Raman spectrometry (RS), photoacoustic spectrometry (PAS), and mass spectrometry (MS). Thus, the amount and quality of information from the analysis of compounds in mixtures has increased. These spectral methods can be coupled with TLC either “of ine” or “online.” The term online can be used instead of the term in situ. Where an authentic reference substance is available, con rmation of the structure of a chromatographically separated unknown compound is possible. As a rule, a single physical method is suf cient for this purpose, e.g., infrared (IRS) or MS. If no reference substance is available, then an attempt can be made to identify the structure with the aid of a spectroscopic method, e.g., nuclear magnetic resonance (NMR), in addition to using IR or MS. High-performance thin-layer chromatography (HPTLC) when compared with high-performance liquid chromatography (HPLC) is more exible with regard to detection strategies associated with the thin-layer technique, including detecting microchemical reactions occurring on the surface of the thin layer, biomonitoring, and the possibility of using surface-enhanced spectroscopy for the identi cation of compounds.
