Detectors and chromatogram scanners

The quantitation of substances separated by TLC may be carried out in several ways. The most common method is to remove the spot from the plate, elute the compound from the adsorbent and measure the concentration of the compound in solution by spectrophotometry, fluorimetry, etc. The elution process has been significantly improved and facilitated with the Eluchrom instrument developed by Sandoz and marketed by Camag (see Fig.3.6). This instrument permits direct elution from the plates via small PTFE cups in a continuous flow-through mode without the necessity of removal of the adsorbent and with the minimum requirement of solvent (usually less than 1 ml). The measuring instruments used are those available for classical solution analysis. A discussion of these instruments is beyond the scope of this book. 

The Vitatron TLD-100 thin-layer densitometer (Vitatron, Dieren, The Netherlands) is a single-beam instrument (Fig.3.11) which has been designed for reflectance, transmission 

The Zeiss PMQ 3 chromatogram analyzer is probably the most versatile thin-film scanner available (Fig.3.13). The system can be used for reflectance, transmission, simultaneous reflectance and transmission and fluorescence quenching. It has two direct fluorescence modes, one with filter emission and surface illumination at a direction of 90° to the surface of the plate, and the other with 45° illumination and monochromatic emission. The instrument can be used for scanning thin-layer chromatograms, paper 

The Berthold 4-pi thin-layer scanner (Fig.3.20) also uses a Geiger—Muller gas-flow detector. Use of the gases methane or argon-methane (9 1) is suggested. The 4-pi system 

Other radiochromatogram scanning systems are available from Baird-Atomic, Packard (Downers Grove, 111., U.S.A.) and Vangard Systems (North Haven, Conn, U.S.A.). 

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