Capillary electrophoresis and open tubular capillary electrochromatography using a magnesia–zirconia coated capillary Original Research Article

A novel magnesia–zirconia coating was fabricated inside fused-silica capillaries. The capillaries coated with magnesia–zirconia exhibited switchable electro-osmotic flow (EOF) whose magnitude and direction can be manipulated by changing the pH of running electrolyte. In Tris electrolyte at high pH (>5.2), the direction was from anode toward cathode, whereas at low pH (<5.2), the direction of EOF was reversed. The magnesia–zirconia coated capillary can be modified by SO42− and alkylphosphonate easily based on strong Lewis acid–base interaction. The separations of six basic compounds were compared on magnesia–zirconia coated capillary and SO42− modified magnesia–zirconia coated capillary under different conditions. It was found that the SO42− modified magnesia–zirconia coated capillary with reversed EOF in Tris–methanol (80/20, v/v) at pH 2.5 was suitable for the separation of the six basic compounds. For the alkylphosphonate modified magnesia–zirconia coated capillary, the alkyl moiety on the inner wall enabled it to separate polycyclic aromatic hydrocarbon (PAH). Six PAHs were separated on the alkylphosphonate modified magnesia–zirconia coated capillary with CH3CN+20 mmol/l Tris (25/75, v/v) as the mobile phase within 13 min. The magnesia–zirconia coated capillary was stable over a wide pH range.