The Use of Modified Silica Gels in TLC and HPTLC

At its beginning only very few sorbente were used as stationary phases in thin-layer chromatography. Along with cellulose and aluminum oxides, porous silica gels played a dominant role. The selectivity of the chromatographic system was in most cases adapted to suit a given separation problem by varying the composition of the mobile phase. It was frequently necessary to use multicomponent mobile phases for this. These phase systems were based on a relatively polar stationary phase and a mobile phase which, in comparison, was less polar to varying extents. To reverse the polarity of the phase system and hence also to increase the range of selectivity, the polar supports of the thin layers were occasionally impregnated with nonpolar liquid stationary phases. A not inconsiderable disadvantage of this method is the fact that portions of the liquid stationary phase are washed out with the mobile phase during chromatographic development and appear in the form of zones of contamination of varying degrees in the region of the mobile phase front. To prevent or at least to limit this, it is necessary to saturate the mobile phase with the liquid stationary phase prior to the chromatographic development. To eliminate this disadvantage, and also because of the relatively poor reproducibility of this method in thin-layer chromatography (as in column liquid chromatography), chemically bonded nonpolar stationary phases were also developed [ 1-5 ].