Chen-Hsing Lin

Determination of enantiomerization barrier of thioridazine by dynamic capillary electrophoresis using sulfated cyclodextrins as chiral selectors

The enantiomerization of thioridazine (THD) using sulfated β‐CDs (S‐β‐CDs) as chiral selectors in a citrate buffer at pH 3.0 was investigated by dynamic CE. The enantiomers of THD were well separated with dual CD systems consisting of S‐β‐CD and a neutral CD. The electropherograms featuring a plateau formation, which indicated the occurrence of the enantiomerization of THD were obtained. The unified equation implemented in the software program DCXplorer was employed to evaluate elution profiles and to determine rate constants of the enantiomerization of THD. Activation parameters were evaluated from temperature‐dependent measurements between 15 and 25°C with an increment of 2°C. The enantiomerization barriers of THD in two different electrophoretic systems were determined. Comparative studies on enantioseparation of THD using S‐β‐CDs with different degree of substitution and positions of sulfate substituent, such as randomly sulfate‐substituted β‐CD, 18‐sulfate‐substituted β‐CD and heptakis(2,3‐dihydroxy‐6‐O‐sulfo)‐β‐CD reveal that the interactions between chiral selectors and THD plays an important role in the enantioseparation and enantiomerization of THD.

Optimization of separation and migration behavior of chloropyridines in micellar electrokinetic chromatography

The separation and migration behavior of pyridine and eight chloropyridines, including three monochloropyridines, four dichloropyridines, and 2,3,5-trichloropyridine were investigated by micellar electrokinetic chromatography using either sodium dodecyl sulfate (SDS) as an anionic surfactant or SDS-Brij 35 mixed micelles. Various parameters such as buffer pH, SDS concentration, Brij 35 concentration and methanol content that affect the separation were optimized. Complete separation of these chloropyridines was optimally achieved with a phosphate buffer containing SDS (30 mM) and methanol (10%, v/v) at pH 7.0. The resolution and selectivity of analytes could be considerably affected by the addition of methanol and/or Brij 35 to the background electrolyte. The migration order of these chloropyridines depends primarily on their hydrophobicity. However, electrostatic interactions may also play a significant role in the determination of the migration order of the positional isomers of chloropyridines.