Retention behaviour of analytes in reversed phase high performance liquid chromatography - A review

The understanding of principles that drive the separation in reversed phase chromatography plays an important role in the prediction of elution of solutes in RP-HPLC. The separation in RP-HPLC is based on the principle of adsorption and partition. In addition, the log P value, pK_a value of the drug, chromatographic parameters like mobile phase pH, buffer concentration, organic modifier and mobile phase additives also influence the retention and selectivity of the analyte. It is found that hydrophobic, electrostatic, hydrogen bonding and other specific interactions between the stationary phase and the solutes along with the hydrophobicity of an analyte molecule (log P) modify the retention behaviour of the analytes. This article gives special attention to the influence of ionization and ion interaction on the separation of analytes. The drug molecules with different log P value containing protonated and deprotonated acids, bases and zwitterions are selected as examples and this article addresses various issues related to method development, relationships between analyte retention and mobile phase pH and pK_a value of the analyte. The advances in this regard, with highlights on topics such as mechanisms of retention and various factors that influence the retention behaviour of analytes is also updated with suitable examples.