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In this work, a [Cu(mal)(bpy)]⋅H2O (mal, L-(-)-malic acid; bpy, 4,4'-bipyridyl) homochiral metal-organic frameworks (MOFs) was synthesized and used for modifying the inner walls of capillary columns by utilizing amido bonds to form covalent links between the MOFs particles and capillary inner wall. The synthesized [Cu(mal)(bpy)]⋅H2 O and MOFs-modified capillary column were characterized by X-ray diffraction, thermogravimetric analysis, particle size distribution analysis, nitrogen absorption characterization, FTIR spectroscopy, SEM, and energy-dispersive X-ray spectroscopy (EDX). The MOFs-modified capillary column was used for the stereoisomer separation of some drugs. The LODs and LOQs of six analytes were 0.1 and 0.25 μg/mL, respectively. The linear range was 0.25-250 μg/mL for ephedrine, 0.25-250 μg/mL for pseudoephedrine, 0.25-180 μg/mL for D-penicillamine, 0.25-120 μg/mL for L-penicillamine, 0.25-180 μg/mL for D-phenylalanine, and 0.25-160 μg/mL for L-phenylalanine, all with R(2) > 0.999. Finally, the MOFs-modified capillary column was applied for the analysis of active ingredients in a real sample of the traditional Chinese medicine ephedra.

Covalent bonding of homochiral metal–organic framework in capillaries for amino acid enantiomer separation by capillary electrochromatography.

A new capillary electrophoresis (CE) method was developed by using graphene oxide (GO) as a stationary phase for the separation of brucine and strychnine. The separation performance, reproducibility and stability of GO-coated capillary were investigated for the analysis of brucine and strychnine. After optimization of the separation conditions, a phosphate solution (40 mM, pH 7.0) containing 25% (v/v) acetonitrile was selected as the running buffer. Compared with uncoated capillary, higher separation efficiency was achieved by GO-coated capillary as a result of the increasing interactions between the analytes and the stationary phase of capillary. The linear ranges of these two alkaloids were 4.0-100.0 μg mL(-1) with a satisfied correlation coefficients (R > 0.9994), and this novel method provided an efficient separation of brucine and strychnine as well as a good reproducibility and stability. Finally, the developed method was successfully applied for the determination of these two alkaloids in a pharmaceutical formulation of traditional Chinese medicines.

& A novel approach was developed for the determination of four catechins, (-)-epigallocatechin gallate, (-)-epigallocatechin, (-)-gallocatechin gallate, and (-)-epicatechin, in tea by micellar electrokinetic chromatography (MEKC) using an acidic phosphate buffer (40 mM, 100 mM sodium dodecyl sulfate, and 30% methanol, pH 3.0). The linear dynamic ranges for the catechins were between 25 and 250 lg=mL, and the graphene oxide-coated capillary offered satisfactory accuracy, precision, and limits of detection. The developed method was employed for the determination of catechins in tea.

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