Coupling Temperature Control with Electrochemically Modulated Liquid Chromatography: Fundamental Aspects and Applications

The primary focus of the doctoral research presented herein has been the integration of temperature control into electrochemically modulated liquid chromatography (EMLC). The combination of temperature control and the tunable characteristics of carbonaceous EMLC stationary phases have been invaluable in deciphering the subtleties of the retention mechanism. The effects of temperature and E{sub app} on the retention of several naphthalene disulfonates were therefore examined by the van' Hoff relationship. The results indicate that while the retention of both compounds is exothermic at levels comparable to that in many reversed-phase separations, the potential dependence of the separation is actually entropically affected in a manner paralleling that of several classical ion exchange systems. Furthermore, the retention of small inorganic anions at constant temperature also showed evidence of an ion exchange type of mechanism. While a more complete mechanistic description will come from examining the thermodynamics of retention for a wider variety of analytes, this research has laid the groundwork for full exploitation of temperature as a tool to develop retention rules for EMLC. Operating EMLC at elevated temperature and flow conditions has decreased analysis time and has enabled the separation of analytes not normally achievable on a carbon stationary phase. The separation of several aromatic sulfonates was achieved in less than 1 min, a reduction of analysis time by more than a factor of 20 as compared to room temperature separations. The use of higher operating temperatures also facilitated the separation of this mixture with an entirely aqueous mobile phase in less than 2 min. This methodology was extended to the difficult separation of polycyclic aromatic hydrocarbons on PGC. This study also brought to light the mechanistic implications of the unique retention behavior of these analytes through variations of the mobile phase composition