Abstract High-performance thin-layer chromatographic pre-coated plates incorporating chemically bonded alkylamino groups have been developed. Their chromatographic properties are largely determined by the alkylamino groups chemically bonded to the surface of the silica gel. Because of the basic p K value of the amino group in aqueous media, the coating can be looked upon as a weak, basic anion exchanger. Polyvalent anions, e.g., nucleotides or sulphonic acids, are retained according to their charge number: the more negative charges the molecule has the greater is the retention. The usage of these pre-coated plates is not restricted to aqueous solvent systems. The way in which organic solvents of various polarities can be used is demonstrated in a number of separations of steroids and phenols.