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

Wei-Bin Tseng ^a, Ming-Mu Hsieh ^b,*, Tai-Chia Chiu ^c,**, Po-Lin Yu ^b, Szu-Hua Chen ^b

^a Department of College of Ecology and Resource Engineering, Wuyi University, China

^b Department of Chemistry, National Kaohsiung Normal University, Taiwan

^c Department of Applied Science, National Taitung University, Taitung, Taiwan

This study developed a sensitive method involving capillary electrophoresis (CE) coupled with ultraviolet absorption for the simultaneous separation of chiral phenothiazine drugs at 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 background electrolyte 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 of the difference in viscosity between the PDDAC-containing background electrolyte and the sample solution, with almost no loss of resolution. The combination of a solid-phase extraction and PDDAC-mediated CE can efficiently improve the sensitivity of the phenothiazine enantiomers. Under optimal conditions, calibration graphs displayed the linear range between 6 and 1500 nM, with relative standard deviation values lower than 3.5% (n ¼ 5). Detection limit ranged from 2.1 to 6.3 nM for target analytes, and 607- to 1555-fold enhancement was achieved. The practicality of using the proposed method to determine five pairs of D,L-phenothiazines in urine is also validated, in which recoveries between recoveries of all phenothiazines from urine ranged from 89% to 101%.

Keywords: Capillary electrophoresis, Chiral separation, On-line concentration, Phenothiazine, Solid phase extraction