Ultrahigh pressure liquid chromatography using elevated temperature

Fast liquid chromatographic (LC) methods are important for a variety of applications. Reducing the particle diameter (dp) is the most effective way to achieve fast separations while preserving high efficiency. Since the pressure drop along a packed column is inversely proportional to the square of the particle size, when columns packed with small particles (<2 μm) are used, ultrahigh pressures (>689 bar) must be applied to overcome the resistance to mobile phase flow. Elevating the column temperature can significantly reduce the mobile phase viscosity, allowing operation at higher flow rate for the same pressure. It also leads to a decrease in retention factor. The advantage of using elevated temperatures in LC is the ability to significantly shorten separation time with minimal loss in column efficiency. Therefore, combining elevated temperature with ultrahigh pressure facilitates fast and efficient separations. In this study, C6-modified 1.0 μm nonporous silica particles were used to demonstrate fast separations using a temperature of 80 °C and a pressure of 2413 bar. Selected separations were completed in 30 s with efficiencies as high as 220,000 plates m−1.