Hydrophilic interaction chromatography (HILIC) has been the subject of a few excellent reviews in recent years and most focused on different factors which impact on the separation of compounds in HILIC mode including column temperature, mobile phase composition, pH, buffer type and concentration. However, there have not been as many studies focusing on the retention mechanism and selectivity in hydrophilic chromatography. In the light of recent development in HILIC stationary phases and their applications, the need to understand the mechanisms that govern the separation in HILIC, which is not purely due to partitioning, and the contribution of stationary surface became a subject of study. This thesis explored the possible mechanisms which might be involved in HILIC chromatography by comparing the retention of test probes on bare silica gel and on a type-C silica hydride phase. In addition, a comprehensive retention and selectivity study of some commercially available hydride-based stationary phases was carried out in the analysis of hydrophobic acids and bases in hydrophilic interaction chromatography (HILIC). The applications of HILIC technique were also addressed in the analysis of plasma and urinary metabolites, impurity profiling and in the separation of 'Legal high' regioisomers. An interest in the HILIC retention mechanism was mainly inspired by the need to understand how to develop the optimal HILIC conditions and the selection of a stationary phase. The retention of a series of positively charged probes on silica gel column was concluded that for this class of compounds both ion-exchange and hydrophilic partitioning were involved in retention. Ion exchange interactions were minimised by increase the ionic strength of the modifier in the mobile phase. The strength of the overall HILIC mechanism was increased with silica gel surface area. The unique properties of silica-hydride phases also assessed and are still not explained in terms of how the retention mechanism of this type of stationary phase is different from the other separation materials used in chromatography. The study confirmed the usefulness of HILIC in many analytical aspects. However, the mixed-interaction mechanisms which operate on different stationary phases for different compounds are still far from understood and more investigation is required.
|Date of Award||2 Jun 2017|
- University Of Strathclyde
|Supervisor||David Watson (Supervisor) & Alexander Gray (Supervisor)|