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An in situ zeolite imidazole metal organic framework-90 (ZIF-90) modified capillary was prepared via the method of solvothermal synthesis. The coating of ZIF-90 was characterized by scanning electron microscopy, energy-dispersive X-ray spectrometry, and EOF. Capillary electrochromatography–based enantioseparation of the basic drugs propranolol (PRO), metoprolol (MET), atenolol (ATE), bisoprolol (BIS), and sotalol (SOT) was performed using lactobionic acid (LA) as the chiral selector. Compared with an uncoated silica capillary, the resolutions are greatly improved (PRO 1.40 → 3.23; MET 1.07 → 3.19; ATE 1.07 → 3.15; BIS 1.16 → 3.41; SOT 1.00 → 2.79). Effects of buffer pH values, proportion of organic additives, concentration of lactobionic acid, and applied voltage were investigated. Graphical abstract Schematic presentation of the preparation of zeolitic imidazolate framework-90 (ZIF-90) modified capillary (ZIF-90@capillary) for enantioseparation of drug enantiomers. The capillary was applied to construct capillary electrochromatography system with lactobionic acid for enantioseparation of basic chiral drugs.

A novel chiral porous column was fabricated by lipase immobilized MIL-100(Fe) biocomposites as chiral stationary phase through covalent coupling and applied to capillary electrochromatographic enantioseparation. MOF-based lipase biocomposites not only enhance stereoselective activities but also improve the stability and applicability of the enzyme. The functionalized porous columns were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and powder X-ray diffraction. The performance of the porous column was evaluated by enantioseparating amino acid enantiomers, affording high resolution over 2.0. Besides, the enantio-resolutions of phenylephrine, phenylsuccinic acid, chloroquine, and zopiclone were also greater than 2.0. The relative standard deviations of run-to-run, intra-, and inter-day repeatability were within 4.0% in terms of resolution and retention time, exhibiting excellent stability of the column. Conceivably, the results show that MOF-based lipase composites as chiral stationary phase offer a highly efficient means for enantioseparation in capillary electrochromatography, attributing to the enhanced enantioselective activities of lipase by highly ordered frameworks. Graphical Abstract

A new enantioselective open-tubular capillary electrochromatography (OT-CEC) was developed employing β-cyclodextrin covalent organic frameworks (β-CD COFs) conjugated gold-poly glycidyl methacrylate nanoparticles (Au-PGMA NPs) as a stationary phase. The resulting coating layer on the inner wall of the fabricated capillary column was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), energy dispersive spectroscopy (EDS), and electroosmotic flow (EOF) experiments. The performance of the fabricated capillary column was evaluated by CEC using enantiomers of seven model analytes, including two proton pump inhibitors (PPIs, omeprazole and tenatoprazole), three amino acids (AAs, tyrosine, phenylalanine, and tryptophan), and two fluoroquinolones (FQs, gatifloxacin and sparfloxacin). The influences of coating time, buffer concentration, buffer pH, and applied voltage on enantioseparation were investigated to obtain satisfactory enantioselectivity. In the optimum conditions, the enantiomers of seven analytes were fully resolved within 10 min with high resolutions of 3.03 to 5.25. The inter- to intra-day and column-to-column repeatabilities of the fabricated capillary column were lower than 4.26% RSD. Furthermore, molecular docking studies were performed based on the chiral fabricated column and as ligand isomers of analytes using Auto Dock Tools. The binding energies and interactions acquired from docking results of analytes supported the experimental data. Graphical Abstract

A fluorinated covalent organic framework composed of 2,3,5,6 -tetrafluoroterephthaldehyde (TFA) and 1,3,5 -tri(4-aminophenyl)benzene (TAPB) is proposed for electrochromatographic separation. TFA-TAPB is for the first time regarded as the stationary phase of capillary electrochromatography. The TFA-TAPB-coated capillary columns exhibited satisfactory separation (resolution values > 1.5) and good reproducibility towards fluoroquinolones. The intraday relative standard deviations (RSDs) of retention time and peak areas were 0.54–0.68% and 1.69–2.82%, respectively. The interday RSDs of retention time and peak areas were less than 1.79% and 2.30%, respectively. The column-to-column RSDs of retention time and peak areas were 0.22–0.73% and 0.74–1.86%, respectively. And, the inter-batch RSDs of retention time and peak areas were less than 0.39% and 1.67%, respectively. Moreover, the possible separation mechanism was discussed, and it was found that the π-π stacking effect, hydrophobic interaction, hydrogen bonding, and fluorous interactions were the main factors. Overall, these results demonstrated that TFA-TAPB has high prospect for CEC separation. Graphical abstract

A capillary coating column was prepared for capillary electrochromatography (CEC) using a novel nanomaterial synthesized by chiral metal–organic frameworks (CMOFs) (Co 2 (L-Trp)(INT) 2 (H 2 O) 2 (ClO 4 ) and chiral molecularly imprinted polymers (CMIPs) as the stationary phase for enantioseparation of amlodipine. The rigid skeleton of CMOFs can be used as a support to reduce the deformation and collapse of CMIPs pores, the high specific surface area of CMOFs can increase the loading of molecular imprinting, while the viscosity of CMIPs improves the stability of stationary phases connected to the inner wall of capillaries. Compared with the capillary-coated columns with CMOFs and CMIPs as stationary phases alone, the novel capillary-coated columns utilizing the synergistic effect of  CMIP@CMOF stationary phases showed a greatly improved chiral recognition (resolution: 0/0 → 5.79). The new nanomaterials synthesized by CMOFs and CMIPs as the stationary phase of CEC chiral resolution system show broad application prospects and potentials in the field of chiral drug/compound separation. Graphical Abstract

A covalent organic framework (COF) named TpPa-1 was designed and synthesized at ambient temperature by an ultrasound-assisted method from 1,3,5-triformylphloroglucinol (Tp) and 1,4-phenylenediamine (Pa-1). It was utilized as a stationary phase in open-tubular capillary electrochromatography (OT-CEC). The column was coated with TpPa-1 using a covalent bonding strategy. The coated capillary was characterized by morphology, crystallography, and mesoporous analysis to confirm the successful fabrication. The OT-CEC method was utilized for the analysis of tetracyclines, sulfonamides, cephalosporins and amino acids with high-resolution (Rs > 1.81) and good precision (RSD < 4.9%). It takes about 12 h from COF preparation to OT-CEC separation. Graphical abstract A covalent organic framework (COF) named TpPa-1 was synthesized at ambient temperature by an ultrasound-assisted method from 1,3,5-triformylphloroglucinol (Tp) and 1,4-phenylenediamine (Pa-1). COF-TpPa-1 modified capillary column was utilized for the analysis of tetracyclines, sulfonamides, cephalosporins and amino acids with high-resolution and good precision.

A novel kind of chiral open-tubular (OT) column was established with homochiral zeolitic imidazolate framework-8 nanomaterials using L-histidine as the chiral carbon center (L-His-ZIF-8). The morphologies of L-His-ZIF-8 nanoparticles and chiral OT column were characterized by scanning electron microscopy. The effects of L-His-ZIF-8 concentrations, pH values, and concentrations of the running buffer on the resolution of the selected chiral compounds were investigated based on miniaturized capillary electrochromatography with amperometric detection system (mini-CEC-AD), respectively. The separation performances of the prepared L-His-ZIF-8@OT chiral columns were explored under the optimal conditions, and the RSDs of run-to-run, day-to-day, and column-to-column reproducibility were less than 6.7% using salbutamol raceme as the model enantiomers. The prepared chiral OT columns have been successfully applied to the enantioseparation of one pair of amino acid enantiomers, two pairs of racemic drugs, and three pairs of neurotransmitter enantiomers. Under the optimum conditions, the prepared OT columns were applied to real-world sample analysis of salbutamol aerosol. The limits of detection of salbutamol raceme were 0.90 μg·mL −1 (S/N = 3), and the recovery was 80.4–82.7%. The assay results indicated that this kind of chiral OT column modified with homochiral L-His-ZIF-8 possesses good reproducibility and stability. This developed mini-OT-CEC-AD system has some attractive characteristics of sensitivity and low cost, providing a potential way for the separation of chiral compounds. Graphic Abstract

Dual-ligand metal–organic frameworks (MOFs) based on tryptophan and camphoric acid were designed and synthesized as the stationary phase of the capillary electrochromatography (CEC) system. This CEC system showed significantly improved enantioseparation ability for nine drugs, compared with the single-ligand MOF stationary phase. Characterization methods such as N 2 adsorption–desorption isotherms and scanning electron microscopy proved that the dual-ligand MOFs possessed excellent 3D spatial structures (ligand ratio is 1:1) which ensured the enantioseparation capability of the CEC system. The influence of ligand types on the chiral selectivity of MOFs was explored using racemic phenylalaninol and its single enantiomers as models. When the chiral type of the ligands is consistent, the enantioseparation ability of the CEC system is better. The chromatographic conditions such as buffer concentration, buffer pH, organic solvent addition ratio, and applied voltage were optimized, and satisfactory repeatability and stability of the CEC system were verified. Additionally, the enantioseparation mechanism of the CEC system was discussed through adsorption kinetic experiments, adsorption isotherm fitting, and thermodynamics. Graphical abstract

This work shows that the metal organic framework (MOF) HKUST-1 of type Cu 3 (BTC) 2 (also referred to as MOF-199; a face-centered-cubic MOF containing nanochannels) is a most viable coating for use in enantioseparation in capillary electrochromatography (CEC). A HKUST-1 modified capillary was prepared and characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectra, elemental analysis and thermogravimetric analysis. CEC-based enantioseparation of the basic drugs propranolol (PRO), esmolol (ESM), metoprolol (MET), amlodipine (AML) and sotalol (SOT) was performed by using carboxymethyl-β-cyclodextrin as the chiral selector. Compared with a fused-silica capillary, the resolutions are improved (ESM: 1.79; MET: 1.80; PRO: 4.35; SOT: 1.91; AML: 2.65). The concentration of chiral selector, buffer pH value, applied voltage and buffer concentration were optimized, and the reproducibilities of the migration times and R s values were evaluated. Graphical abstract Schematic presentation of the preparation of a HKUST-1@capillary for enantioseparation of racemic drugs. Cu(NO 3 ) 2 and 1,3,5-benzenetricarboxylic acid (BTC) were utilized to prepare the HKUST-1@capillary. Then the capillary was applied to construct capillary electrochromatography system with carboxymethyl-β-cyclodextrin (CM-β-CD) for separation of basic racemic drugs.

Chiral phenyl aromatic compounds (CPACs) are widely used in drug development, food/cosmetic production, and other organic synthesis processes, and their different enantiomers have distinct physiological activities and application differences. A double-layer metal–organic framework composite (MOF-on-MOF) was obtained by in situ synthesis of chiral metal–organic framework (CMOM-3S) on the surface of an iron-based metal–organic framework (NH 2 -MIL-101(Fe)). According to our investigation, MOF-on-MOF composite was for the first time applied to the stationary phase of capillary electrochromatography (CEC), and enantioseparations of eight CPACs were accomplished. Compared with single CMOM-3S, the enantioseparation performance of the coated capillary columns based on NH 2 -MIL-101(Fe)@CMOM-3S was improved by 34.07 ~ 720.0%. The R-/S-mandelic acid in actual sample (apricot leaves) was detected by the newly CEC system to be 0.0118 mg mL −1 and 0.0523 mg mL −1 , respectively. The spike recoveries were 96.60 ~ 104.7%, indicating its good stability and accuracy. In addition, the selective adsorption capacity of MOF-on-MOF composites was verified by adsorption experiments. Graphical Abstract