A SYSTEMATIC STUDY OF IMPREGNATION OF THIN-LAYERS WITH DIFFERENT ION-PAIRING REAGENTS AND BY DIFFERENT METHODS

The efficiency of a variety of techniques used for impregnation of sil ica gel layers with tetramethylammonium bromide (TMA), tetrabutylammon ium bromide (TBA), cetyltrimethylammonium bromide (CTMA), and trioctyl methylammonium chloride (TOMA) has been determined. The absolute conce ntrations of the different ion-pairing reagents on the layers were mea sured by spectrophotometry, potentiometry, and thermogravimetry. When development-type impregnations were used, a concentration gradient was observed on the layer in the direction of the development. The slope of the gradient depended on the impregnation technique used and the na ture of the ion-pairing reagent. Smoother gradients were obtained by u se of overdevelopment than by impregnation by other types of developme nt, e.g. development up to a given distance in a saturated or unsatura ted chamber, or by use of OPLC or a sandwich chamber. Horizontal and v ertical dipping by use of an immersion device resulted in almost unifo rm distribution of the reagent on the layer. The concentrations of the ion-pairing reagents on the lever increased with increasing dipping t ime, except for CTMA-impregnated layers, for which longer dipping time s resulted in desorption. The retention and resolution of model compou nds reflected the concentration of ion-pairing reagents in the station ary phase.