Possibilities and limits of an on-line coupling of thin-layer chromatography and FTIR-spectroscopy

Summary

A new method of an on-line coupling of TLC and FTIR spectroscopy is introduced. By the combination of a computer controlled x—y-stage with a “diffuse reflectance unit” and an FTIR spectrometer using commercially available GC-IR software it is possible to obtain chromatograms of a TLC separation. The chromatograms can be generated both frequency dependent as spectral windows of a certain range and frequency independent as Gram-Schmidt trace. During the measurement the series of interferograms are saved on a hard disk, so that the desired TLC-FTIR spectra can be immediately computed after the end of the measurement. If necessary, a stationary measurement can be performed at the position of maximum substance concentration with high resolution and coaddition of interferograms. The quality of the TLC-FTIR spectra is sufficient for identification of unknown substances and discrimination of closely related substances. There are different ways to present the huge amount of received data: as a 3-dimensional stacked plot of the measured spectra, as horizontal sections through that stacked plot, as a contour plot, with which a rapid check of peak purity is possible, or as frequency dependent chromatograms at any wavelength of interest.