Enantioseparation of phenothiazines through capillary electrophoresis with solid phase extraction and polymer based stacking

This study developed a sensitive method involving capillary electrophoresis (CE) coupledwith ultraviolet absorption for the simultaneous separation of chiral phenothiazine drugsat nanomolar concentration levels. The method consists of hydroxypropyl-g-cyclodextrin(Hp-g-CD) as a chiral selector and poly (diallyldimethylammonium chloride) (PDDAC)-based CE. Five pairs of D,L-phenothiazines were baseline separated using a backgroundelectrolyte containing 0.9% PDDAC, 5 mM Hp-g-CD, and 100 mM tris(hydroxymethyl)aminomethane(Tris)-formate (pH 3.0). The five pairs were successfully stacked on the basis ofthe difference in viscosity between the PDDAC-containing background electrolyte and thesample solution, with almost no loss of resolution. The combination of a solid-phaseextraction and PDDAC-mediated CE can efficiently improve the sensitivity of the phenothiazineenantiomers. Under optimal conditions, calibration graphs displayed the linearrange between 6 and 1500 nM, with relative standard deviation values lower than 3.5%(n = 5). Detection limit ranged from 2.1 to 6.3 nM for target analytes, and 607- to 1555-foldenhancement was achieved. The practicality of using the proposed method to determinefive pairs of D,L-phenothiazines in urine is also validated, in which recoveries betweenrecoveries of all phenothiazines from urine ranged from 89% to 101%.