Similar to infrared spectra, Raman spectra yield unique spectral bands related to fundamental vibration modes suitable for identification purposes [59]. Typical thin-layer sorbents produce weak Raman spectra and so the general problem of background interference in in situ infrared measurements is less of a problem. On the other hand, directly recorded Raman spectra are weak giving rise to poor sensitivity. The techniques of resonance Raman spectroscopy and surface enhanced Raman spectroscopy (SERS) have long since promised to solve this problem without great progress, at least not in thin-layer chromatography. SERS, in particular, is a very sensitive technique but requires application of a metal hydro sol to the layer or transfer of the separation to a flexible metal-impregnated substrate to enhance the signal intensity . Both approaches have not moved out of the research phase and dedicated instruments for use with thin-layer chromatography are unavailable.