Polydopamine-based permanent coating capillary electrochromatography for auxin determination

A novel, simple, and economical method for the preparation of open-tubular capillary column using polydopamine coating was reported for the first time. After the capillary was filled with dopamine solution for 20 h, polydopamine was formed and deposited on the inner wall of capillary as permanent coating via the oxidation of dopamine by the oxygen dissolved in the solution. Moreover, the electroosmotic flow of the coated capillaries was measured to be dependent on the repetitive coating times. The performance of the polydopamine-coated capillary electrochromatography was validated by the analysis of four auxins, indole-3-butyric acid (IBA), 2,4-dichlorophenoxyacetic acid (dCPAA), indole-3-acetic acid (IAA), and phenoxyacetic acid (PAA). The precisions (RSD, n = 5) were in the range of 1.6–2.4% for migration time, 4.0–6.5% for peak area response, and 3.6–4.7% for peak height response for the four auxins at 1 μg mL−1 level. The detection limits were 0.185, 0.172, 0.177, and 0.259 μg/mL for IBA, dCPAA, IAA, and PAA, respectively. The method was successfully used to the determination of IAA in the culture media of IAA-producing bacteria.