Chromatographic Performance of Silica-Based Stationary Phases in High Temperature Liquid Chromatography: Pharmaceutical Applications

High temperature liquid chromatography is currently well established in separation sciences. The decrease of mobile phase viscosity with temperature provides fast separations with high efficiency, limiting excessive backpressure. Furthermore, the water polarity decreases with temperature allowing a reduction of the organic modifier content in the mobile phase. These advantages are already observed for temperature below 100°C. Recently, the commercialization of dedicated instrumentation for preheating and cooling the mobile phase, and of new stationary phases stable at high temperature containing carbon, zirconia, titania or polymeric material, allows a routine use of high temperature liquid chromatography (HTLC). The latter stationary phases could however exhibit high retentions and different selectivity in comparison with the traditional silica-based columns. Therefore, embedded, hybrid or new silica- based stationary phases, possessing similar chromatographic behaviour and good thermal resistance at temperatures as high as 100°C, are often selected. Kinetic, stability and chromatographic performance of a silica-based stationary phase (Zorbax Stable Bond) were evaluated up to a temperature of 120°C. This chromatographic support was successfully used for separating numerous drugs at ambient and high temperatures. Improvements of performance due to temperature increase were reported, such as the decrease in analysis time (separations in only few seconds) and the peak shape improvements (higher efficiency and lower asymmetry). Furthermore, several modifications of selectivity and the possibility to use a lower content of organic modifier into the mobile phase were demonstrated.