Separation of amino acid enantiomers by a capillary modified with a metal-organic framework

A type of homochiral metal-organic framework (MOF), [Zn-2(D-Cam)(2)(4,4'-bpy)](n) (D-Cam = D-(+)-camphoric acid; bpy = bipyridyl), was synthesized and utilized as the chiral stationary phase for capillary electrochromatography. X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Fourier-transform infrared spectroscopy (FTIR) were performed to characterize the MOF. The MOF particles were attached to the inner walls of the capillary columns through covalent linkages, and the MOF-modified capillary columns were characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Finally, the enantiomeric separation of phenylalanine and tyrosine was achieved in the MOF-modified capillary columns. The limit of detection (LOD) and the limit of quantitation (LOQ) were 0.1 mu g mL(-1) and 0.3 mu g mL(-1), respectively, for the four analytes. The linear range was 0.3-250 mu g mL(-1) for D-phenylalanine, 0.3-200 mu g mL(-1) for L-phenylalanine, 0.3-220 mu g mL(-1) for D-tyrosine and 0.3-180 mu g mL(-1) for L-tyrosine, all with an R-2 > 0.999. The stability of the MOF-modified columns was measured with RSDs. DL-Phenylalanine exhibits intraday, interday and column-to-column precisions of 0.57-12.13%, whereas the data for DL-tyrosine were 0.45-9.93%.