Study of the Performances of Thin-Layer Chromatography I. A Phenomenological Approach

Abstract

So-called HPTLC is a development of TLC carried out using small particles, usually about 5 μm in diameter, with a narrow size distribution, as currently used in HPLC. It is shown that whereas conventional TLC works in experimental conditions where resistance to mass transfer controls the spot length, resulting in the characteristic elongated spots, HPTLC works under such conditions that molecular diffusion determines the spot diameter. Thus spots are circular and in a chromatogram all spots tend to have similar diameters unless diffusion coefficients vary widely from one compound to the other. Still better performances could be obtained using somewhat coarser particles—probably in the 10 – 20 μm range—with which development would be faster, could be cheaper, and would give larger spots for a given resolution, resulting in easier sampling and less drastic specifications for the scanning photodensitometer.