How to Retain Polar and Nonpolar Compounds on the Same HPLC Stationary Phase with an Isocratic Mobile Phase

High performance liquid chromatography (HPLC) stationary phases can be segregated by their ability to separate either polar on nonpolar compounds, that is, reversed-phase materials (C18, C8) strongly retain nonpolar solutes with polar solutes eluting at or near the void volume, and hydrophilic interaction chromatography (HILIC) and normal phase columns strongly retain polar analytes with nonpolar compounds being essentially nonretained (1). Increasingly, many analyses such as those encountered in drug discovery, proteomics, and metabolomics can be more complex with solutes encompassing a broad range of polarities. To overcome these deficiencies in column performance, more complex schemes of analysis might have to be devised to provide successfully qualitative and quantitative information about solutes with differing hydrophobicities and hydrophilicities. These approaches can include various types of sample preparation or two-dimensional chromatographic methods (2) as well as using chromatographic extremes of pH (3) and temperature (4). In most cases, such methodology can be cumbersome, time consuming, and damaging to your instrument and the HPLC column. In many instances, it would be desirable to have a stationary phase that can retain both polar and nonpolar compounds in an isocratic run so that a single separation strategy can be devised to analyze samples with a broad range of polarities.