Combination of poly(diallyldimethylammonium chloride) and hydroxypropyl-γ-cyclodextrin for high-speed enantioseparation of phenothiazines by capillary electrophoresis

Abstract

High-speed capillary electrophoresis (CE) enables the simple, rapid, and inexpensive analysis of large sets of chiral samples in the pharmaceutical industry. Hence, we developed a novel method for separating enantiomers of d,l-phenothiazines simply and rapidly, based on using poly(diallyldimethylammonium chloride) (PDDAC) as an additive and hydroxypropyl-γ-cyclodextrin (Hp-γ-CD) as a chiral selector in capillary electrophoresis. Adding 0.9% PDDAC to the background electrolyte generated a stable, high, and reversed electroosmotic flow (EOF). Hp-γ-CD not only worked as a complexing agent to increase the chiral resolution between d,l-phenothiazines but also decreased the effective electrophoretic mobility of these drugs. Combining PDDAC and Hp-γ-CD as buffer additives enabled CE to achieve a high-speed enantioseparation of five pairs of d,l-phenothiazines. A decrease in capillary length and an increase in the intensity of the electric field further shortened the separation time. When the background electrolyte contained 0.9% PDDAC, 5mM Hp-γ-CD, and 75mM formic acid (pH 3.0), enantioseparation of the d,l-phenothiazines was attained within 230s by applying a capillary length of 32.5cm and an electric field of 292Vcm−1. The limit of detection (LOD) of the d,l-phenothiazines at a signal-to-noise ratio of 3 ranged from 2 to 8μM. We demonstrated the feasibility of this method by detecting the five pairs of d,l-phenothiazines in urine samples.