Capillary electrophoresis and open tubular capillary electrochromatography using a magnesia-zirconia coated capillary

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+20mmol/l Tris (25/75, v/v) as the mobile phase within 13min. The magnesiazirconia coated capillary was stable over a wide pH range.