A novel in situ strategy for the preparation of a β‐cyclodextrin/polydopamine‐coated capillary column for capillary electrochromatography enantioseparations

Abstract

Inspired by the chiral recognition ability of β-cyclodextrin and the natural adhesive properties of polydopamine under alkaline conditions, in this study, a rapid and in situ modification strategy was developed to fabricate β-cyclodextrin/polydopamine composite material coated-capillary columns for open tubular capillary electrochromatography. The results of scanning electron microscopy, FTIR spectroscopy, streaming potential, and electro-osmotic flow studies indicated that β-cyclodextrin/polydopamine was successfully fixed on the inner wall of the capillary column. This coating can be achieved within 1 h affording a greatly reduced capillary preparation time. The performance of the β-cyclodextrin/polydopamine-coated capillary was validated by the analysis of seven pairs of chiral analytes, namely epinephrine, norepinephrine, isoprenaline, terbutaline, verapamil, tryptophane, carvedilol. Good enantioseparation efficiencies were achieved for all. For three consecutive runs, the relative standard deviations for the migration times of the analytes for intraday, interday, and column-to-column repeatability were in the range of 0.41-1.74, 1.03-4.18, and 1.66-8.24%, respectively. Moreover, the separation efficiency of the β-cyclodextrin/polydopamine-coated capillary column did not decrease obviously over 90 runs. The strategy should also be feasible to introduce and immobilize other chiral selectors on the inner walls surface of capillary columns.

Recent developments in open tubular capillary electrochromatography from 2016 to 2017

“…Scanning electron microscopy (SEM) has become an indispensable characterisation method for a visual confirmation of the surface morphology of coated surfaces. SEM images of successfully coated surfaces were described to show rough surfaces , hilly or bumpy surfaces , with distinct shapes of the embedded material , good layer density and homogeneity or uniformity , and more importantly significant layer thickness as opposed to the smooth surfaces seen in bare silica surfaces. Some SEM scans were performed on flat silica surfaces for detailed characterisation because of the inherent difficulty in successfully imaging wall coatings for a capillary format.…”

“…Fourier transform‐infra red spectroscopy (FT‐IR) has become requisite to ascertain formation of desired covalent bonds, verifying the chemical structure of the synthesised SP and to confirm actual attachment of the material onto the capillary . Two structural characterisations emerging as support to elucidate the chemical structures of embedded SP are X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS).…”

“…The separation was attributed to the chiral structure of the hybrid material and the high homogeneity resulting from the coating method. The employment of β‐cyclodextrin as SP material for enantioseparations is well known, whereby Guo and co‐workers developed a direct method of immobilisation on the capillary wall by forming a β‐CD/PDA composite utilising the adhesive properties of PDA . Separation performance was validated with good separations of seven pairs of chiral isomers with resolutions (R) from 1.23 (carvedilol enantiomers) to 3.45 (terbutaline enantiomers) and column efficiencies (number of theoretical plates, N) from 53 833 and 64 718 (tryptophan enantiomers) to 190 336 and 440 250 (epinephrine enantiomers).…”

“…Polydopamine (PDA) continues to be significantly employed as surface modifying agent to immobilise SP substrates onto capillary columns for OT‐CEC. Easily formed in situ through the self‐polymerisation of dopamine, this mussel‐inspired material exhibits strong adhesive quality while easily forming thin layer films on surfaces , allowing hydrophilic interactions to embed frameworks nanoparticles and biomaterials . An innovative approach was used by Zhang and co‐workers for the deposition of TiO 2 nanoparticles into a column by a liquid phase deposition (LPD) process .…”

Applications of polydopamine modifications in capillary electrophoretic analysis

“…The enantioselectivity of β‐cyclodextrin (β‐CD) was investigated by Guo et al. by employing β‐CD/PDA as stationary phase. The β‐CD/PDA hybrid coatings, introduced by physical adhesive method, were applied for individual analysis of seven pairs of chiral substances including chiral drugs, neurotransmitters, and amino acids.…”