Modulation of Electroosmotic Flow in Open Tubular Capillary Electrochromatography by Chitosan-Assisted Titanium Oxide Nanoparticles Liquid Phase Deposition

Abstract

Electroosmotic flow is one of the most important driving forces in capillary electrophoresis, which can control the migration velocity and direction of the target substance, thus affecting the separation efficiency and reproducibility of capillary electrophoresis. In this study, a facile method was developed for the preparation of TiO2/chitosan open tubular capillary electrochromatography for modulating electroosmotic flow in capillary electrophoresis. The magnitude and direction of electroosmotic flow were modulated by changing a series of coating preparation parameters, such as deposition time of (NH4)2TiF6 and H3BO3, the concentration of chitosan, and the concentration ratio of (NH4)2TiF6 and chitosan. The results showed that when the concentration of (NH4)2TiF6 was below 2 mg/mL, the surface of the capillary was not modified completely by phosphate ion by Lewis acid–base interaction, resulting in an anodic electroosmotic flow. Furthermore, the feasibility and stability of the column were assessed by separation of nucleotides and alkaloid compounds. With the TiO2/chitosan liquid phase deposition columns with the concentration ratio of 3:7 [(NH4)2TiF6:chitosan], alkaloids were baseline separated within 11 min. The baseline separation of the four nucleotides was achieved using the TiO2/chitosan-coated columns with the concentration ratio of 1.8:7 [(NH4)2TiF6:chitosan]. Furthermore, the relative standard deviations of migration times for inter-day, intra-day, and column-to-column repeatability of the TiO2/chitosan-coated columns with the concentration ratio of 3:7 [(NH4)2TiF6:chitosan] were all less than 5.8%. The strategy of liquid phase deposition of TiO2 nanoparticles provides a promising approach for modulation electroosmotic flow.