DEVELOPMENT, OPTIMIZATION AND APPLICATIONS OF HIGH RESOLUTION SEPARATION AND EXTRACTION TECHNIQUES

Abstract

Chromatography is a separation technique in which a mixture of components is applied as a narrow initial zone to a stationary phase and the components are subjected to differential migration by the action of the flow of mobile phase which may be a liquid, gas or supercritical fluid. In other words, chromatography is primarily an analytical tool effective for the separation of mixtures in which qualitative and quantitative information of the separated components can be obtained. During the last decade or so, the use of high performance chromatographic techniques for chemical and biochemical investigations has increased at a phenomenal rate. This growth has been reflected by an increase in the number of scientific journals devoted almost entirely to chromatographic methods. The ever increasing demands on high resolution chromatographic separations have stimulated the extensive research on new and improved techniques and approaches, including small bore columns, novel stationary phases and new detection systems. Over the past twenty years, several new high performance separation techniques have been developed. These include capillary gas chromatography (GC), high performance liquid chromatography (HPLC), supercritical fluid chromatography (SFC) and capillary electrophoresis (CE). Capillary GC and HPLC are well established techniques which have received wide acceptance and are currently being employed in many applications in the chemical and life sciences. Even though the phenomena of supercritical fluid processes and behaviour, and of electrophoresis have been known as early as in the 18th century, it is only in the last decade that there has been a revival of interest in the use of these techniques for practical applications. In the case of SFC, the possibilities of performing separations of high molecular weight, labile and non-volatile compounds at higher efficiencies and lower temperatures, and the compatibility of most supercritical fluids with gas and liquid chromatographic detectors have generated enormous research interest in the area. These advantages, together with the superior solvation properties possessed by supercritical fluids, have prompted the use of these fluids not only as chromatographic mobile phases, but also as extraction solvents. As a result, both SFC and superc1itical fluid extraction (SFE) have become important tools for many analytical applications where they are generally considered to complement respectively, HPLC and GC, and conventional extraction techniques such as liquid-liquid partition and Soxhlet extraction. Capillary electrophoresis (CE), despite its shorter history compared to SFC, has developed into an exciting and extremely powerful separation technique in recent years. It represents yet another important development in the separation sciences where high speed and extremely efficient separations are readily attainable. Moreover, the technique is amenable to the use of very small sample sizes (nl range) and can be automated very easily. Since their introduction, SFC and CE have demonstrated impressive results in several areas of applications. However, these techniques are still only in their early stages of development and there is plenty of scope for further development before their full potential may be realised. Towards this end, the present work serves to investigate the potential of SFC/SFE and CE. The approach initially taken is to develop and optimize the current or new analytical methodologies associated with these two techniques. This would be followed by the application of the newly developed approaches to the investigation of scope beyond current practices. This dissertation is in two parts : Part one is concerned with the use of supercritical fluids in chromatography and extraction. The second part covers the development of capillary electrophoretic techniques. In Chapter 1, the background of these techniques and the general aims of this work are introduced. Investigations on supercritical fluid chromatography and extraction are described in Chapter 2. The development of separation methodologies based on capillary electrophoresis is discussed in Chapter 3. In Chapter 4, conclusions from these investigation are presented.