A method is described for obtaining Fourier transform infrared (FT-IR) absorbance spectra of substances separated on silica gel thin-layer chromatographic (TLC) plates. The separated TLC spot is scraped off and loaded onto the sample pan of a thermogravimetric analyzer (TGA)/FT-IR. The FT-IR spectrum of the sample is obtained after the sample is thermally desorbed from the silica gel. Spectra are easily identified for samples present at level of 20 μg per TLC spot. A detection limit of 0.8 μg is reported for analysis of methyl benzoate. The total time required for sample preparation and thermal desorption/FT-IR analysis was six to seven minutes. The relationship between the spectrum peak intensity and the furnace heating rate was also studied. This method can be applied to thermally stable substances which can be desorbed from thermally stable TLC stationary phases.
Xiao Chen and Ronald B. Smart, "Analysis of Thin-Layer Chromatography Spots by Thermal Desorption/Fourier Transform Infrared Spectrometry," Appl. Spectrosc. 45, 1322-1326 (1991)