| Capillary electrochromatography (CEC) is a relatively new micro-separation technique that combines the high efficiency of capillary electrophoresis (CE) and the high selectivity of high performance liquid chromatography (HPLC). Accordingly, it has attracted more and more attention in recent years. Up to now, monolithic columns have been considered as the most suitable stationary phases for CEC, due to their simple preparation procedure, unique properties and no needs for frits.Polymer monolithic columns for CEC with an improved configuration were prepared, in which there are stationary phases on both sides of detection window. Therefore, a discontinuity of electroosmotic flow, conductivity and electric field strength in CEC columns with a conventional configuration was eliminated. Separation methods for nucleosides, acidic and basic compounds as well as humic degradation compounds were developed in CEC with methacrylate-based monolithic stationary phases.Based on homologue series method, a method for the determination of hold-up time in reverse-phase capillary electrochromatography was developed. The hold-up times measured with homologue series method and thiourea, an electroosmotic flow marker, were compared. Results show that thiourea has the migration behavior of positively charged solutes. An abnormal phenomenon of the dependence of the retention factors for neutral species on applied voltage was observed in the experiment, and possible reasons were discussed.With chromatographic zone sharping effect and ultralong injection, a concentration factor for benzoin of 22,000 was obtain. To our best knowledge, it is the highest detection sensitivity improvement for a neutral species by on-line concentration in CEC. With the combination of the chromatographic zone sharping effect and field amplified sample stacking effect, the sensitivity of caffeine was improved by a factor of 24,000.
|
PDF Full Text Request