ABSTRACT
It is welllmown that the overwhelming majority of both thin-layer chromatographic (TLC) and high-peformance liquid chromatographic (HPLC) separations are carried out on silica or on silica-based reversed-phase [RP, mainly octadecylsilica (ODS)] supports. However, the acidic character of the free silanol groups exert a considerable impact on the retention behavior of both silica and silicabased supports: Basic solutes are more strongly bonded on the silica surface than neutral or acidic ones [1]. Besides their advantageous retention characteristics (good separation capacity, excellent mechan· ical stability, versatility of the methods for binding various organic ligands to the surface of silica), the application of silica and modified silica stationary phases shows marked disadvantages too [2]. Thus, strongly polar pollutants cannot be easily separated, and the silicabased supports are not stable at alkaline pH, making it difficult to separate strongly basic compounds [3]. As the TLC or RP-TLC plates are used only for one analysis, the stability of the stationary phase at alkaline pH is of secondary importance.
