The silanol group and its role in liquid chromatography

Silica is the most widely used material in chromatography. Silica supports are still superior to other supports. There are, however, several problems with silica-based materials: severe peak tailing in the chromatography of basic compounds, limited pH stability, and irreproducibility for the same chemistry columns. The silanol group plays a key role in the chromatographic properties of silica. Therefore, this review discusses the current state of knowledge on silica surface chemistry and the impact of the chemistry on chromatography of basic solutes. The influence of the silica surface on the stability of bonded phases is also described. We discuss recent developments in IR and NMR spectroscopy of the silica surface, modem understanding of silica surface chemistry, and recent achievements in chromatography of basic solutes. HPLC of organic bases is troublesome due to poor understanding of the mechanisms responsible for difficult chromatography of the solutes. A significant part of the review concerns HPLC of organic bases and it emphasizes the importance of the ion-exchange mechanism for the retention of the bases. The paper discusses how to avoid and how to use ion-exchange for chromatography of organic bases. Factors controlling ion-exchange mechanisms on siliceous supports are discussed in detail. (C) 1997 Elsevier Science B.V.