Conventional TLC, linear and circular HPTLC are compared by using in-situ reflectance measurements. Chromatographic resolution, time requirement and reproducibility of quantitative scanning of the different TLC methods are investigated by means of three separation problems: benzodiazepines, corticosteroids, polycyclic aromatic hydrocarbons.In all three application examples, which were chosen without prejudice, the circular developing mode with subsequent quantitative scanning showed certain advantages over the corresponding linear HPTLC techniques. These were in the case of Benzodiazepines: Better reproducibility of quantitative assessment.
Corticosteroids:Better resolution and slightly better quantitative reproducibility.Polycyclic aromatic hydrocarbons: Chromatography considerably faster.
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
The role of Analytical Chemistry in the professional training, offered by the Department of Chemistry at Basel Institute of Technology, is outlined. Some auricular details of theoretical and experimental courses are given together with typical examples of projects which have been accomplished
by students.
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