Considerations of mechanical precision required for optical in‐situ scanning of circular (U‐chamber) HPTL chromatograms

Abstract

When time is a consideration, then of course total analysis time including sample application and quantitative assessment has to be kept reasonably short. Automatic scanning of an entire chromatogram, or the part of interest, is a suitable approach to shorten analysis time. However, certain requirements with respect to mechanical precision have to be met.The CAMAG TLC/HPTLC Scanner [3] provides means for the automatic scanning of circular chromatograms by three different modes (Figure 1). In each case three parameters can be preselected: A = length of scan, B = distance to the next track, and N = number of scans.The radial scanning mode is appropriate when several or all fractions of a sample are to be scanned before the instrument moves on to the next sample. When corresponding fractions of different samples are to be scanned successively, and these fractions are sufficiently spaced from neighbouring zones, peripheral scanning I is recommended. In this case, of course, automatic scanning of several tracks with a preselected distance B will be the exception. If the space between fractions is very small, the peripheral type I1 scanning mode, i.e. the slit parallel to the direction of scan, is suitable to give very accurate results. It is necessary to advance the plate after each complete rotation