Determination of 13--Retinoic Acid and Its Metabolites in Plasma by Micellar Electrokinetic Chromatography Using Cyclodextrin-Assisted Sweeping for Sample Preconcentration.

The online preconcentration technique, cyclodextrin-assisted sweeping (CD-sweeping), coupled with micellar electrokinetic chromatography (MEKC) was established to determine 13-cis-retinoic acid (13--RA), all--retinoic acid (all--RA) and 4-oxo-13--retinoic acid (4-oxo-13--RA) in human plasma. A CD-sweeping buffer (45 mM borate (pH 9.2), containing 80 mM sodium dodecyl sulfate (SDS) and 22 mM hydroxypropyl β-CD (HP-β-CD) was introduced into the capillary and, then, the sample dissolved in 70 mM borate (pH 9.2): methanol = 9:1 () was injected into capillary by pressure. The separation voltage was 23 kV. Compared to the conventional cyclodextrin-micellar electrokinetic chromatography (CD-MEKC) method, the new technique achieved 224-257-fold sensitivity enrichment of analytes. The limits of detection of 13--RA, all--RA were 1 ng/mL, whereas that of 4-oxo-13--RA was 25 ng/mL in plasma. The linear ranges of 13--RA, all--RA were between 15 and 1000 ng/mL, whereas that of 4-oxo-13--RA was between 75 and 1500 ng/mL. The coefficient of correlation between the concentration of analytes and peak area ratio of analytes and internal standard (2, 4-dihydroxy-benzophenone) for intra-day ( = 3) and inter-day ( = 5) analyses were both greater than 0.999. The optimized experimental conditions were successfully applied to determine 13--retinoic acid and its metabolites in plasma samples from a patient during the administration of 13--RA for treating acne.