| Capillary electrochromatography (CEC) is a newly developed miniaturized technology that combines the advantages from both capillary electrophoresis (CE) and high performance liquid chromatography (HPLC). In CEC, high electrical field is applied across a packed or coated capillary column to drive the mobile phase. Because of the"plug"like flow profile of electro-osmotic flow, in contrast to parabolic flow profile in pressure driven flow, CEC has high separation efficiency compared to HPLC. However, in practice, when CEC was used without pressure, often on a commercial CE instrument, there were problems and difficulties associated with bubbles formation and column dry-out. These problems can be solved by a pressurized CEC (pCEC) system, in which a mobile phase is driven by both a pressurized flow and an electroosmotic flow (EOF). In such a system, a pressure can be applied to the capillary column to suppress bubble formation. Quantitative sample introduction in pCEC can be easily achieved through a rotary-type injector. Therefore, the sample elution order may be manipulated by changing the ratio of pressure to voltage. Most importantly, it is amenable for a solvent gradient mode, similar to that in HPLC, by programming the composition of mobile phone. Monolithic columns have been regarded as the fourth generation separation medium and considered as the most suitable stationary phases for CEC, due to their simple preparation procedure, low backpressure, unique properties and no need for frits. In this study, hydrophilic interaction chromatography-based monolithic column was prepared and used for separation of polar and basic melamine, which is usually difficult to analyze by a reversed phase column.1. Fundamental aspects of CEC and pCEC as well as monolithic columns in both theory and practice were reviewed. 2. Methacrylatebased monolithic column was prepared in 100μm i.d. capillary column in situ using butylmethacrylate, ethylene dimethacrylate and 2-acrylamido-2-methylpropanesulfonic acid. In the study, the monolithic column with hydrophilic interaction mechanism was demonstrated. The applications of the column in pCEC, CEC and micro- high performance liquid chromatography (micro-HPLC) for separation of non-polar compounds has been carried out and the three separation modes were compared. The effects of composition of mobile phase pH value, concentration of the buffer, the flow rate of pump and voltage were investigated and optimized.3. Hydrophilic interaction monolithic column was prepared in 100μm i.d. capillary in situ using butylmethacrylate, ethylene dimethacrylate and 3-[Dimethyl-[2-(2-methylprop-2-enoyloxy)ethyl]azaniumyl]propane-1-sulfonate. In the study, the hydrophilic interaction behavior of the monolithic column was demonstrated. The application of the column in pressurized capillary electrochromatography (pCEC) for separation of melamine with ultraviolet detection has been studied. The effects of composition of mobile phase pH value, concentration of the buffer, the flow rate of pump and voltage were investigated. The optimum separation for melamine were achieved with a mobile phase of 0.01 mol/L phosphate buffer (pH 3.0) : acetonitrile (v/v=80:20), voltage at 3 kV and UV detection at 215 nm . The limits of detection (LODs) (S/N=3) for standard sample of melamine was 0.05μg/mL. The method is simple, accurate and works well without using the ion-pairing agent. The powdered milk and liquid milk were analyzed quantitatively by pCEC using hydrophilic interaction monolithic column. It is shown that this method is promising in the routine analysis of melamine.4. Melamine in milk was determined using the hydrophilic interaction column. Experimental conditions were optimized systematically. The results from pCEC analysis showed that this column is suitable for quantitative analysis of melamine in milk.
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