Silica and other materials as supports in liquid chromatography. Chromatographic tests and their importance for evaluating these supports. Part I

Reversed-phase liquid chromatography (RP HPLC) has become a powerful and wi dely employed technique in the separation and analysis of a great variety o f compounds with different functionalities. The most common type of station ary phase for RP-HPLC consists of nonpolar, hydrophobic organic species (e. g., octyl, octadecyl) attached by siloxane bonds to the surface of a silica support. In the first part of this article, a description of the many bene ficial properties that make porous silica the most employed support in RP-H PLC will be presented, starting from the synthesis of silica. It is notewor thy that the chromatographic properties of the final column are strictly co rrelated to the preparation type. A silica surface possesses a number of attractive properties, but also some drawbacks. Unreacted or residual silanols interact with basic compounds an d can induce peak tailing, which means a loss in chromatographic performanc e. This problem has lead many manufacturers to produce stationary phases wi th reduced silanol activity which improve dramatically the peak shape of ba sic compounds. In the second part of this review, different approaches are proposed to obtain less reactive stationary phases.