Authors:Heinz Hauck, Olga Bund, Walter Fischer, and Michael Schulz
Miniaturization is general trend in modern analytical methods, with the main targets of increasing sensitivity, shortening analysis times drastically, and reducing the quantity of consumables per analysis. In planar chromatography a first step in this direction was the development of modern high-performance TLC (HPTLC). Compared with conventional TLC, the layers are characterized by smaller adsorbent material particle sizes and a slight reduction in layer thickness. A major final step in the direction of miniaturized planar chromatography are the new ultra-thin layers. In contrast with those on TLC and HPTLC plates, these layers are no longer based on granular adsorbents, but have a monolithic structure based on a silica gel matrix. This means there are no longer separate particles, as in TLC and HPTLC. Furthermore, no binder is needed to fix the layer on the glass plate. To be suitable for chromatographic purposes, the monolithic silica gel of these new ultra-thin layers has meso- and macro pores, with fine capillaries penetrating the layer. The layer thickness of approximately 10 μm is considerably less than that of conventional TLC and HPTLC layers. The exciting properties of these new UTLC silica gel plates, especially their selectivity and separation efficiency, are demonstrated by separations of steroids, pesticides, and some dyestuffs.