Search

In recent years, artificial materials with double helix structure have attracted widespread attention due to their unique properties such as the DNA like double-helicity, intrinsic chirality and diverse functional groups. Developing novel chiral stationary phases (CSPs) for capillary electrochromatography enantioseparation is of intriguing interest. Herein, a novel homochiral zeolite-like metal-organic framework (ZMOF) JLU-Liu23 with unique DNA like double-helicity structure was firstly utilized as the CSP in open tubular capillary electrochromatography (OT-CEC) for enantioseparation of chiral monoamine neurotransmitters and analogues. Owing to the unique DNA like double-helicity structure of the homochiral ZMOF JLU-Liu23, the good enantioseparation of four monoamine neurotransmitters and analogues was achieved on the prepared homochiral ZMOF JLU-Liu23 coated capillary column. The relative standard deviations (RSDs) of the analytes migration time for intra-day, inter-day and column-to-column were in the range of 0.3-0.6%, 0.8-2.2% and 3.5-6.5%, respectively.

The popularity of novel nanoparticles coated capillary column has aroused widespread attention of researchers. Metal organic frameworks (MOFs) with special structure and chemical properties have received great interest in separation sciences. This work presents the investigation of HKUST-1 (Hong Kong University of Science and Technology-1, called Cu3(BTC)2 or MOF-199) nanoparticles as a new type of coating material for capillary electrochromatography. For the first time, three layers coating (3-LC), five layers coating (5-LC), ten layers coating (10-LC), fifteen layers coating (15-LC), twenty layers coating(20-LC) and twenty-five layers coating (25-LC) capillary columns coated with HKUST-1 nanoparticles were synthesized by covalent bond with in situ, layer-by-layer self-assembly approach. The results of scanning electron microscopy (SEM), X-ray diffraction (XRD) and plasma atomic emission spectrometry (ICP-AES) indicated that HKUST-1 was successfully grafted on the inner wall of the capillary. The separating performances of 3-LC, 5-LC, 10-LC, 15-LC, 20-LC and 25-LC open tubular (OT) capillary columns were studied with some neutral small organic molecules. The results indicated that the neutral small organic molecules were separated successfully with 10-LC, 15-LC and 20-LC OT capillary columns because of the size selectivity of lattice aperture and hydrophobicity of organic ligands. In addition, 10-LC and 15-LC OT capillary columns showed better performance for the separation of certain phenolic compounds. Furthermore, 10-LC, 15-LC and 20-LC OT capillary columns exhibited good intra-day repeatability with the relative standard deviations (RSDs; %) of migration time and peak areas lying in the range of 0.3-1.2% and 0.5-4.2%, respectively. For inter-day reproducibility, the RSDs of the three OT capillary columns were found to be lying in the range of 0.3-5.5% and 0.3-4.5% for migration time and peak area, respectively. The RSDs of retention times for column-to-column for three batches of 10-LC, 15-LC and 20-LC OT capillary columns were in the range from 2.3% to 7.2%. Moreover, the fabricated 10-LC, 15-LC and 20-LC OT capillary columns exhibited good repeatability and stability for separation, which could be used successively for more than 120 runs with no observable changes on the separation efficiency.

Covalent organic frameworks (COFs) have attracted much attention because of their permanent nanoscale porosity and higher surface area compared to zeolites as well as robustness. COFs have great potential in several fields such as hydrogen storage, gas separation, and catalysis. However, COFs have not yet been applied in capillary electrochromatography. Herein, covalent organic frameworks-LZU1 (COF-LZU1) was used as the stationary phase in open-tubular capillary electrochromatography for the first time. Compared to the monoliths used in electrochromatography, the preparation technique of a COF-LZU1-coated capillary was simple and practical. The baseline separation of model analytes including alkylbenzenes, polyaromatic hydrocarbons, and anilines by the COF-LZU1-coated capillary was achieved based on the size selectivity of COF-LZU1 porous structure and hydrophobic interactions between the model analytes and organic ligands of COF-LZU1. The load capacity of the COF-LZU1-coated capillary for naphthalene was 0.6mg/mL. For three consecutive runs, the intraday relative standard deviations (RSDs) were 1.4-2.6% for the migration time and 2.7-8.7% for the peak area. The interday RSDs were 1.3-3.9% for the migration time and 3.7-9.7% for the peak area. The column-to-column reproducibility of migration time was in the range 1.0-3.9%. Moreover, the coated capillary was used for >300 runs with no changes in the separation efficiency. Thus, COFs have great potential in capillary electrochromatography and may provide a new method for chromatographic separation.