Recent Developments in Type C Stationary Phases: Exploiting the Versatility of Silica Hydride Materials - Joseph J. Pesek & Maria Matyska

TYPE C™ silica is a relatively new chromatographic material that has been finding ever-increasing use in the last few years. The properties exhibited by these stationary phases are often significantly different than the ordinary silica used for most commercial products. While all TYPE C phases can be utilised in the reversed-phase, organic normal phase and aqueous normal phase modes, there are some unique capabilities within each retention mode that have resulted in innovative method development strategies with great success. Some of the more challenging separation problems involve polar compounds; two approaches for the analysis of hydrophilic compounds are described in this report.

Introduction
TYPE C silica, based on a surface of Si-H, was introduced many years ago. However, it has only been recently that some of the unique chromatographic features of this material have been discovered and exploited in solving challenging separation problems. This report focuses on the capabilities of these stationary phases for the separation of hydrophilic materials in two modes: aqueous normal phase (ANP) that utilizes high organic content mobile phases and in reversed-phase using high aqueous content mobile phases. For descriptions about the chromatographic properties of TYPE C in the organic normal phase, earlier reports have provided examples of separations utilising this separation mechanism [1,2].

The chromatographic retention and separation of polar compounds continues to be a challenging analytical problem. The versatility and ruggedness of reversed-phase chromatography for separations based on hydrophobic interactions has not been matched by any single method for hydrophilic species. A number of approaches have been developed for polar compound retention but many are limited in their applicability or have other serious drawbacks. For example polar compounds can be derivatised to make them amenable to RP methods, but this is often timeconsuming or not very reproducible.