Preparation of a β-Cyclodextrin-Based Open-Tubular Capillary Electrochromatography Column and Application for Enantioseparations of Ten Basic Drugs

Abstract

An open-tubular capillary electrochromatography column was prepared by chemically immobilized β-cyclodextrin modified gold nanoparticles onto new surface with the prederivatization of (3-mercaptopropyl)-trimethoxysilane. The synthesized nanoparticles and the prepared column were characterized by transmission electron microscopy, scanning electron microscopy, infrared spectroscopy and ultraviolet visible spectroscopy. When the column was employed as the chiral stationary phase, no enantioselectivity was observed for ten model basic drugs. So β-cyclodextrin was added to the background electrolyte as chiral additive to expect a possible synergistic effect occurring and resulting in a better separation. Fortunately, significant improvement in enantioselectivity was obtained for ten pairs of drug enantiomers. Then, the effects of β-cyclodextrin concentration and background electrolyte pH on the chiral separation were investigated. With the developed separation mode, all the enantiomers (except for venlafaxine) were baseline separated in resolutions of 4.49, 1.68, 1.88, 1.57, 2.52, 2.33, 3.24, 1.63 and 3.90 for zopiclone, chlorphenamine maleate, brompheniramine maleate, dioxopromethazine hydrochloride, carvedilol, homatropine hydrobromide, homatropine methylbromide, venlafaxine, sibutramine hydrochloride and terbutaline sulfate, respectively. Further, the possible separation mechanism involved was discussed.

Fig 1. The chemical structures of the ten chiral analytes.

Fig 2. (A) TEM micrograph of gold nanoparticles dispersed in hexane, on a carbon film 400-mesh copper grid; (B) Visible absorption spectrum of gold nanoparticles dispersed in hexane.

λ_max = 519 nm.

Fig 3. FT-IR spectra of (A) free SH-β-CD and (B) β-CD-GNPs based capillary; SEM photographs of (C) bare capillary and (D) etched β-CD-GNPs capillary.

Fig 4. The effect of pH on the EOF mobility.

BGE: pH 2.5, 25 mM Tris-H₃PO₄ buffer solution, 20kV. (a) blank capillary; (b) β-CD-GNPs based capillary. OTCEC conditions: 49 cm × 50 μm i.d., Sample: thiourea, Separation voltage, 20 kV.

Fig 5. Effect of pH (A) and β-CD concentration (B) on R_S of the 10 chiral analytes (1) zopiclone, (2) chlorphenamine maleate, (3) brompheniramine maleate, (4) dioxopromethazine hydrochloride, (5) carvedilol, (6) homatropine hydrobromide, (7) homatropine methylbromide, (8) venlafaxine, (9) sibutramine hydrochloride and (10) terbutaline sulfate.

Fig 6. Typical electropherograms of the 10 chiral analytes on (A) bare capillary and (B) etched capillary.

BGE: 20 kV, (A) 10 mM β-CD, pH 2.5, 30 mM Tris-H₃PO₄, (B) 5 mM β-CD, pH 2.5 (sibutramine hydrochloride, pH 2.0), 25 mM Tris-H₃PO₄. (the numbers of the drugs are the same as in Fig 5).

Fig 7. Illustration of chiral separation of positively charged analytes on β-CD-GNPs modified capillary.