Preparation and study of a capillary electrochromatographic column prepared by conjugating ß-CD COFs and gold-poly glycidyl methacrylate nanoparticles.

A new enantioselective open-tubular capillary electrochromatography (OT-CEC) was developed employing ß-cyclodextrin covalent organic frameworks (ß-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.

In situ growth of dual-responsive polymer as coating for open tubular capillary electrochromatographic separation of epimedins.

Recently, open tubular capillary electrochromatography (OT-CEC) has captured considerable interest; its efficient separation capability hinges on the interactions between analytes and polymer coatings. However, in situ growth of stimuli-responsive polymers as coatings has been rarely studied and is crucial for expanding the OT-CEC technique and its application. Herein, following poly(styrene-maleicanhydride) (PSM) chemically bonded onto the inner surface of the capillary, a dual pH/temperature stimuli-responsive block copolymer, P(SMN-COOH), was prepared by in situ polymerizing poly(N-isopropylacrylamide) carboxylic acid terminated [P(N-COOH)] in PSM. An OT-CEC protocol was first explored using the coated capillary for epimedins separation. As a proof of concept, the developed OT-CEC system facilitated hydrogen bonding and tuning the hydrophilic/hydrophobic interactions between the test analytes and the P(SMN-COOH) coating by varying buffer pH and environmental temperature. Four epimedins with similar chemical structures were baseline separated under 40 °C at pH 10.0, exhibiting dramatical improvement in separation efficiency in comparison to its performance under 25 °C at pH 4.0. In addition, the coated capillary showed good repeatability and reusability with relative standard deviations for migration time and peak area between 0.7 and 1.7% and between 2.9 and 4.6%, respectively, and no significant changes after six runs. This work introduces a paradigm for efficient OT-CEC separation of herbal medicines through adjusting the interactions between analytes and smart polymer coatings, addressing polymer coating design and OT-CEC challenges.

Effective enrichment and separation of three flavonoids from Ohwia caudata (Thunberg) H. Ohashi using magnetic layered double hydroxide/ZIF-8 composites and pCEC.

In this study, Fe3O4@ZnCr-layered double hydroxide/zeolitic imidazolate frameworks-8 (MLDH/ZIF-8) magnetically functionalized composites were synthesized by co-precipitation and in situ growth based on the advantages of LDHs and ZIF-8 using Fe3O4 nanoparticles as a magnetic substrate to obtain adsorbents with excellent performance. Moreover, the composite was used for the efficient enrichment of flavonoids in Chinese herbal medicines. The internal structures and surface properties were characterized by SEM, Fourier transform infrared spectroscopy, X-ray diffraction and so on. MLDH/ZIF-8 exhibited a large specific surface area and good paramagnetic properties. The MLDH/ZIF-8 magnetic composite was used as a magnetic solid-phase extraction (MSPE) adsorbent, and a MLDH/ZIF-8 MSPE-pressurized capillary electrochromatography coupling method was developed for the separation and detection of flavonoids (luteolin, kaempferol and apigenin) in a sample of the Chinese herb Ohwia caudata (Thunberg) H. Ohashi. The relevant parameters affecting the extraction efficiency were optimized to determine the ideal conditions for MSPE. 5 mg of adsorbent in sample solution at pH 6, vortex extraction for 5 min, elution with 1.5 mL of ethyl acetate for 15 min. The method showed good linearity in the concentration range of 3-50 µg mL-1 with correlation coefficients of 0.9934-0.9981, and displayed a relatively LODs of 0.07-0.09 µg mL-1. The spiked recoveries of all analytes ranged from 84.5% to 122.0% with RSDs (n=3) between 4.5% and 7.7%. This method is straightforward and efficient, with promising potential in the separation and analysis of active ingredients in various Chinese herbal medicines.

Covalent organic frameworks: spotlight on applications in the pharmaceutical arena.

Covalent organic frameworks (COFs) have much potential in the field of analytical separation research due to their distinctive characteristics, including easy modification, low densities, large specific surface areas and permanent porosity. This article provides a historical overview of the synthesis and broad perspectives on the applications of COFs. The use of COF-based membranes in gas separation, water treatment (desalination, heavy metals and dye removal), membrane filtration, photoconduction, sensing and fuel cells is also covered. However, these COFs also demonstrate great promise as solid-phase extraction sorbents and solid-phase microextraction coatings. In addition to various separation applications, this work aims to highlight important advancements in the synthesis of COFs for chiral and isomeric compounds.

[Box: see text].

Chiral hydroxyl-controlled covalent organic framework-modified stationary phase for chromatographic enantioseparation.

Chiral covalent organic frameworks (CCOFs) possess a superior chiral recognition environment, abundant pore configuration, and favorable physicochemical stability. In the post-synthetic chiral modification of COFs, research usually focused on increasing the density of chiral sites as much as possible, and little attention has been paid to the influence of the density of chiral sites on the spatial structure and chiral separation performance of CCOFs. In this article, 1,3,5-tris(4-aminophenyl) benzene (TPB), 2,5-dihydroxyterephthalaldehyde (DHTP), and 2,5-dimethoxyterephthalaldehyde (DMTP) served as the platform molecules to directly establish hydroxyl-controlled COFs through Schiff base condensation reactions. Then the novel chiral selectors 6-deoxy-6-[1-(2-aminoethyl)-3-(4-(4-isocyanatobenzyl)phenyl)urea]-ß-cyclodextrin (UB-ß-CD) were pended into the micropore structures of COFs via covalent bond for further construction the [UB-ß-CD]x-TPB-DMTP COFs (x represents the density of chiral sites). The chiral sites density on [UB-ß-CD]x-TPB-DMTP COFs was regulated by changing the construction proportion of DHTP to obtain a satisfactory CCOFs and significantly improve the ability of chiral separation. [UB-ß-CD]x-TPB-DMTP COFs were coated on the inner wall of a capillary via a covalently bonding strategy. The prepared open tubular capillary exhibited strong and broad enantioselectivity toward a variety of chiral analytes, including sixteen racemic amino acids and six model chiral drugs. By comparing the outcomes of chromatographic separation, we observed that the density of chiral sites in CCOFs was not positively correlated with their enantiomeric separation performance. The mechanism of chiral recognition [UB-ß-CD]x-TPB-DMTP COFs were further demonstrated by molecular docking simulation. This study not only introduces a new high-efficiency member of the COFs-based CSPs family but also demonstrates the enantioseparation potential of CCOFs constructed with traditional post-synthetic modification (PSM) strategy by utilizing the inherent characteristics of porous organic frameworks.

Enantiomeric analysis of chiral phenyl aromatic compounds by coated capillary electrochromatography based on a MOF-on-MOF stationary phase.

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 (NH2-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 NH2-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.

Chiral zeolite beta used as stationary phase for enantioseparation in miniaturized open tubular capillary electrochromatography with amperometric detection.

BACKGROUND: With the rapid growth of the demand for optically pure compounds in the fields of biology, medicine and stereospecific synthesis, it is of great importance to develop efficient, economical, simple enantioseparation and analysis methods. Open tubular capillary electrochromatography (OT-CEC) has attracted much attention in the field of chiral separation, but its column capacity and the sensitivity of common-used optical detection are relatively low. Zeolite beta nanomaterial is both enantioselective and size-selective, providing suitable chiral microenvironment for chiral recognition, and amperometric detection (AD) avoids the low sensitivity caused by the short optical path in optical detection to some extent. RESULTS: Zeolite beta nanomaterials with different particle sizes (25, 50 and 200 nm) were synthesized, and the morphology and structure were characterized by scanning electron microscopy and X-ray diffraction. Then, a novel chiral OT column was prepared by one-step method using zeolite beta nanomaterial as chiral stationary phase, and its separation performance was characterized by miniaturized CEC with AD (mini-CEC-AD) device. Under the optimum conditions, six groups of chiral drugs achieved baseline separation. Norepinephrine enantiomers were used for evaluating the inter-day, intra-day and inter-column reproducibility of the prepared open-tubular column. The relative standard deviations of migration time, peak area, resolution and selectivity factor were within 8.7 %. The limits of detection for norepinephrine enantiomers were 0.18 µg mL-1 (S/N = 3), and the average recoveries were in range of 96.7-105.0 %. This developed method has been successfully applied to the analysis of impurity enantiomer in potassium dichromate (+)-norepinephrine injection sample. SIGNIFICANCE: Zeolite beta nanomaterial was used as the stationary phase to prepare chiral OT columns for the first time, and this one-step preparation method is simple and easy. The introduction of zeolite beta enriches the types of chiral stationary phase materials in electrochromatographic columns, and mini-OT-CEC-AD system provides an alternative for fast enantioseparation of chiral compounds.

Multilayer coatings based on gold nanoparticles and polymers with bovine serum albumin as a functional layer for the chiral separation in capillary electrochromatography.

In this study, we developed physically adsorbed multi-layer coatings using poly-l-lysine or poly(diallyldimethylammonium chloride) and gold nanoparticles, which were functionalized with bovine serum albumin for the chiral separation in electrochromatography. The approach involves sequentially depositing positively charged polymers and negatively charged citrate-stabilized gold nanoparticles. By repeating this modification cycle, we created two- and four-layer coatings, which were sequentially functionalized with albumin forming three- and five-layer coatings that were finally applied for the separation of enantiomers of dl-tryptophan. The formed coatings exhibit stability across a pH range of 2-10 and feature a dense, uniform surface, as confirmed by scanning electron microscope images. The number of layers impacted nanoparticle deposition density, with five-layer coatings being denser than three-layer ones. Five-layer coatings enable baseline separation of dl-tryptophan enantiomers, whereas three-layer coatings require the presence of albumin in the background electrolyte for separation. Therefore, increasing the number of layers and gold nanoparticles density enhances albumin active center concentration on capillary walls, improving the separation of dl-tryptophan enantiomers. The five-layer coatings can be easily fabricated and possess good repeatability of analytes migration time.

Rapid and in-situ preparation COFs coated capillary by adsorption method for the separation and determination of phthalate ester using CEC.

As a novel class of stationary phase materials, covalent organic frameworks (COFs) have shown great promise in open-tubular capillary electrochromatography. However, the current preparation of COFs coating capillaries heavily relies on tedious and time-consuming covalent bond methods. In this work, a novel, simple and rapid adsorption method was developed for fabrication of TPB-DMTP COF (fabricated from 1,3,5-tris(4-aminophenyl)benzene (TPB) and 2,5-dimethoxyterephthalaldehyde (DMTP)) coated capillary. Due to the crystallization process of the COF is greatly shortened because pre-modification capillary does not require silane coupling agent, this method enables the rapid preparation of COFs-coated capillaries. The organic molecular building units only need 25 min to form a stable COFs coating on the inner wall of a capillary by this method. To our knowledge, this is the shortest method for preparing COFs coated capillary up to now. The performance of the TPB-DMTP COF coated capillary was evaluated by using phthalate esters as model analytes. The results demonstrated that the TPB-DMTP COF coated capillary has excellent repeatability and stability. The relative standard deviations (RSDs) of the analyte's retention time of intra-day, inter-day and column-to-column were in the range of 0.05 %-0.27 %, 0.31 %-0.63 % and 0.31 %-0.88 %, respectively. And, no significant changes were observed in separation efficiency and retention time after over 200 runs. Finally, the TPB-DMTP COF coated capillary was applied for the determination of phthalates in marketed plastic bag and the recovery ranged from 88.0 % to 114.0 %.

In situ growth of imine-based covalent organic framework as stationary phase for open-tubular capillary electrochromatographic separation.

Designing advanced stationary phases to improve separation efficiency is essential in capillary electrochromatography. Due to their outstanding performance, covalent organic frameworks have recently demonstrated considerable promise in the field of separation science. Herein, an open-tubular capillary electrochromatography method was reported using porous imine-based covalent organic framework with sufficiently available interaction sites as stationary phase. The imine-based covalent organic framework coated capillary was easily prepared via an in situ growth method at room temperature, and its separation performance was evaluated, indicating the high separation efficiency for three types of analytes, including herbicides, polybrominated dibenzofurans, and bisphenols. Moreover, the imine-based covalent organic framework coated capillary showed good reproducibility and stability, with intraday (n = 3), interday (n = 3), and column-to-column (n = 3) relative standard deviations of retention time and peak areas of less than 5%. The separation efficiency of the coated capillary remained unchanged even after 200 runs and the maximum theoretical plates reached up to 85 595 N/m for 4,4'-ethylidenebisphenol. It was predicted that the imine-based covalent organic framework stationary phase would be a strong contender for chromatographic separation with high efficiency.

Facile room-temperature synthesis of a spherical mesoporous covalent organic framework for capillary electrochromatography.

Herein, a spherical covalent organic framework COF TAPB-DMTP was facilely synthesized from 2,5-dimethoxyterephthalaldehyde (DMTP) and 1,3,5-tri-(4-aminophenyl)benzene (TAPB) as monomers. COF TAPB-DMTP with regular mesoporous and excellent mass transfer ability was first introduced into the capillary and immobilized on the inner wall of the capillary through a simple in situ growth method. Through various characterization results, COF TAPB-DMTP was successfully prepared and modified onto the capillary inner wall. The separation performance and potential of COF TAPB-DMTP modified capillary column was explored. The new developed COF modified column achieved a highly efficiency and selective separation between analytes with different properties, including halogeno benzenes, alkylbenzenes, phenols and sulfonamides. Satisfactory stability and reproducibility were observed on COF TAPB-DMTP modified columns. The intraday, interday and three batch columns relative standard deviations were all less than 1.85 % for the retention time. The separation performance of prepared column has no significant change after 90 continuous runs. Additionally, the COF TAPB-DMTP modified capillary column was successfully used for separation and detection of triazole antifungal drugs in human plasma, and the recoveries of three antifungal drugs (fluconazole, isavuconazole and posaconazole) in spiked samples were in the range of 98.6-100.8 %, 92.4-102.1 % and 99.9-107.5 %, respectively. This self-made column showed excellent application potential in chromatography separation science.

Recent developments in capillary and microchip electroseparations of peptides (2021-mid-2023).

This review article brings a comprehensive survey of developments and applications of high-performance capillary and microchip electromigration methods (zone electrophoresis in a free solution or in sieving media, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography, and electrochromatography) for analysis, micropreparation, and physicochemical characterization of peptides in the period from 2021 up to ca. the middle of 2023. Progress in the study of electromigration properties of peptides and various aspects of their analysis, such as sample preparation, adsorption suppression, electroosmotic flow regulation, and detection, are presented. New developments in the particular capillary electromigration methods are demonstrated, and several types of their applications are reported. They cover qualitative and quantitative analysis of synthetic or isolated peptides and determination of peptides in complex biomatrices, peptide profiling of biofluids and tissues, and monitoring of chemical and enzymatic reactions and physicochemical changes of peptides. They include also amino acid and sequence analysis of peptides, peptide mapping of proteins, separation of stereoisomers of peptides, and their chiral analyses. In addition, micropreparative separations and physicochemical characterization of peptides and their interactions with other (bio)molecules by the above CE methods are described.

Open tubular capillary electrochromatography with dual-responsive polymer as coating for separation of chromones.

Fabricating polymeric coatings that are responsive to multiple/dual stimuli is crucial and remains a major challenge in the development of highly efficient open tubular capillary electrochromatography (OT-CEC). In this study, a pH and temperature-responsive block copolymer, poly(styrene-maleic anhydride 2-dimethylamino ethyl methacrylate), P(St-MAn-DMAEMA), was designed and synthesized. Using P(St-MAn-DMAEMA) as the coating, an OT-CEC protocol was constructed for the analysis of chromones. The morphology and hydrophobicity-hydrophilicity of the polymeric coating could change via varying the environmental conditions, affecting the separation efficiency of OT-CEC. Interestingly, the best performance of OT-CEC was achieved at pH 9.7 and 45 °C via tuning the interactions between the coating and the analytes. Additionally, the proposed OT-CEC method exhibited a good linear range for the detection of the three test chromones from 10.0 to 100.0 µM, with all correlation coefficients (R2) >0.997. The coatings also had good stability and reusability. This work provides an approach for the preparation of new multiple-stimuli-responsive polymeric coatings for the establishment of OT-CEC systems.

[Recent advances in carbon dots-based chromatographic separation materials].

Chromatographic column is the core of chromatographic separation, and chromatographic separation material is considered the soul of the chromatographic column. The type and characteristics of the chromatographic separation material directly determine the separation mode and performance of chromatographic columns. The development and preparation of separation materials with novel structures and good separation performance is an ongoing hotspot in chromatography research. Given rapid developments in nanoscience and technology, nanomaterials with unique surface functional groups and large specific surface areas have attracted extensive attention and great interest from researchers in the field of separation science. Carbon dots (CDs), a new type of zero-dimensional fluorescent carbon nanomaterials, have been widely used in bioimaging, light-emitting diodes, sensing, catalysis, drug delivery, and other applications since they were first reported in 2004. These nanomaterials present several advantages over other types of separation materials, including a simple preparation process, low toxicity, easy functionalization, excellent biocompatibility, and photobleaching resistance. In addition, compared with traditional carbon nanomaterials such as graphene and carbon nanotubes, CDs have abundant surface functional groups, nanoscale sizes, and moderate adsorption properties. Hence, when CDs-based new materials are applied as a stationary phase for column chromatography, they can provide rich reaction sites and ensure the uniformity of the chromatographic packing process. The use of CDs can effectively avoid the peak-tailing phenomenon caused by the strong interaction of large π-conjugated systems with some analytes and improve the efficiency of the chromatographic column. As such, these nanomaterials show good application prospects in the field of chromatographic separation. In this review, the development history, classification, and synthesis strategies of CDs are briefly described. We then focus on the development of CDs-based chromatographic separation materials by systematically reviewing the recent advances in the use of CDs-based materials as a stationary phase for high-performance liquid chromatography (including hydrophilic interaction, reversed-phase, mixed-mode, and chiral chromatography), gas chromatography, and capillary electrochromatography, with special emphasis on the preparation methods and applications of various stationary phases. Finally, the development prospects of CDs and future research efforts on these materials are also analyzed and discussed. This review can provide guidance on the rational design and application of new CDs-based chromatographic separation materials.

[Preparation of porous organic cage and its use as chiral stationary phase for capillary electrochromatography].

Porous organic cages (POCs) are a unique type of microporous materials composed of discrete molecules with internal cavities that are accessible to various compounds. In this study, a prismatic chiral POC with good thermochemical stability was synthesized by condensing (1R,2R)-diaminocyclohexane and 3,3',5,5'-teturonic-4,4'-biphenediol via the Schiff base reaction and characterized by proton nuclear magnetic resonance spectroscopy, infrared (IR) spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy. The IR spectrum of the POC revealed a strong characteristic absorption peak at 1635 cm-1, indicating that it formed imine bonds (C=N). The absorption peak at 3425 cm-1 was attributed to the stretching vibrations of -OH, the absorption peaks at 2925 and 2858 cm-1 were attributed to the stretching vibrations of N=C-H and C-H, and the absorption peaks at 1446 and 1383 cm-1 were attributed to the stretching vibrations of C=C-H and C=C in the benzene ring. High-resolution mass spectral analysis of the POC showed a molecular ion peak at m/z 1363.7228, indicating its successful synthesis. TGA was performed from 25 to 800 ℃ at a rate of 10 ℃/min, and the results of this analysis showed that the POC was stable up to approximately 300 ℃. The POC was dissolved in dichloromethane and uniformly coated on the inner wall of a quartz capillary via the dynamic coating method to prepare a capillary electrochromatographic column. The experimental results revealed that the chiral electrochromatographic column could not only resolve ofloxacin, Troger's base, 2-amino-1-butanol, and 1-phenyl-1-amyl alcohol but also separate the isomers of o-, m-, and p-toluidine and o-, m-, and p-chloroaniline, indicating its good chiral separation ability. Investigation of the optimal separation conditions for ofloxacin, Troger's base, 2-amino-1-butanol, and 1-phenyl-1-amyl alcohol revealed that the voltage, buffer solution concentration, and pH significantly affected their separation degree. In particular, the optimal separation voltage for ofloxacin, Troger's base, and 2-amino-1-butanol was 15 kV, while that for 1-phenyl-1-amyl alcohol was 17 kV. The optimal buffer concentration and pH for ofloxacin, Troger's base, 2-amino-1-butanol, and 1-phenyl-1-amyl alcohol were 0.100 mol/L and 7.5. Under optimal chromatographic conditions, the resolution values for ofloxacin, Troger's base, 2-amino-1-butanol, and 1-phenyl-1-pentanol were 1.80, 3.33, 1.69, and 1.18, respectively. The results collectively demonstrate that the prepared POC may serve as a good chiral stationary phase for capillary electrochromatography with a certain chiral resolution ability and has good application prospects in chromatographic separation.

[Recent developments in the application of covalent organic frameworks in capillary electrochromatography].

Capillary electrochromatography (CEC) has received increased attention from the academic community because it combines the excellent selectivity of high performance liquid chromatography (HPLC) and the high efficiency of capillary electrophoresis (CE). Selecting the most appropriate stationary phase material is crucial to achieve better separation effects in CEC. In recent years, a considerable number of materials, such as graphene oxide, proteins, metal organic frameworks, and covalent organic frameworks (COFs), have been widely used as stationary phases in CEC to further improve its separation performance and extend its scope of potential applications. Among these materials, COFs have shown great application prospects in CEC owing to their unique properties, which include high porosity, large surface area, excellent stability, tunable pore size, and high designability of the framework structure. This review systematically summarizes published papers on the development and application of COFs in CEC from 2016 to 2023. First, two COF-based capillary columns (i. e., open-tube CEC columns and monolithic CEC columns) and their preparation methods are introduced. Second, the applications of CEC based on COF stationary phases in the separation of environmental endocrine disruptors, pesticides, aromatic compounds, amino acids, and drugs, particularly chiral drugs, are systematically summarized. The separation mechanism of CEC based on COF stationary phases is also introduced. At present, the good separation ability of COF-based CEC is mainly attributed to two factors: 1) The size exclusion effect of the pores of the COF stationary phase. Because of differences in the sizes of their organic molecular building units and side chains, COFs have varying pore sizes and topological structures. Thus, target analytes smaller than the pores of the COFs can enter the frameworks and interact with them during separation. On the other hand, target analytes larger than the pores of the COFs cannot enter the frameworks and interact with them during separation; thus, they can be separated. 2) The interactions between the target analytes and side chains (e. g., hydrophobic interactions, hydrogen bonding, π-π interactions, etc.) of the COFs. Since COFs usually contain alkyl side chains, aromatic structures, and oxygen and/or nitrogen atoms with high electronegativity, various interactions could occur between the COFs and target analytes. Finally, directions for the future development and strategic application of CEC based on COF stationary phases are proposed. We believe that future research in CEC based on COF stationary phases should focus on the following aspects: 1) The use of cheminformatics to design and construct COFs to improve the efficiency of COF capillary column preparation; 2) the development of milder methods to synthesize COFs that can meet the requirements of high performance COF capillary columns; and 3) in-depth research to explore the separation mechanism of CEC based on COF stationary phases to provide theoretical guidance for developing CEC methods suitable for the separation and analysis of complex samples.

Sulfonic acid functionalized monolithic column for high selectivity capillary electrochromatography separation.

A new nano-scale spherical vinyl-functionalized covalent organic polymer (TAPT-DVA-COP) with uniform sizes around 300 nm was initially constructed using 2,5-divinyl-1,4-benzaldehyde (DVA) and 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) as monomers. Then, a sulfonic acid (-SO3H) modified COP termed COP-SO3H was developed based on post-sythesis method employing TAPT-DVA-COP as precursor. Capillary electrochromatography (CEC) monolithic columns were fabricated using the physical doping technique to exhibit the application potential of TAPT-DVA-COP and COP-SO3H. Compared to the TAPT-DVA-COP monolithic column, the COP-SO3H monolithic column achieved a highly selective separation between analytes with different properties, including monosubstituted benzenes, alkylbenzenes, hydroxybenzoates, nucleoside bases, and biogenic amines. Non-covalent interaction (NCI) analysis and experimental data show that the synergism of the sulfonic acid group and aromatic moieties on COP-SO3H endows the new stationary phase with diverse interactions, including ion exchange, hydrophobic, π-π and hydrogen bonding. In addition, the COP-SO3H monolithic column exhibited good reproducibility and excellent potential for the determination of hydroxybenzoates in compact powders and alkylbenzenes in effluent samples.

Recent developments in electromigration techniques related to pharmaceutical and biomedical analysis - A review.

The analysis of pharmaceutical compounds is an important research topic as the use of different drugs affects people's daily life for the treatment of diseases. In addition to the widespread use of the internet, counterfeit drugs have appeared in the market. The development of modern analytical techniques, reliable, precise, sensitive, and rapid methods, has provided powerful means of analysis used in various fields such as drug production, quality control, determination of impurities and/or metabolites, biochemistry, pharmacokinetics, etc. Analytical techniques so far used in the pharmaceutical analysis include high-performance liquid chromatography (HPLC), gas chromatography (GC), super/sub-critical fluid chromatography (SFC), and capillary electromigration techniques such as capillary electrophoresis (CE) and rather rarely capillary electrochromatography (CEC). CE has some advantages over other techniques, e.g., very high efficiency, reduced costs (use of minute volumes of solvents and samples), the possibility to use different separation mechanisms, etc. In this review paper, the main features and limitations of the capillary electromigration techniques (especially CE) are discussed. Some selected applications of CE to the analysis of pharmaceutical compounds published in the period 2021-2023 (May) are reported.

Review of recent advances in development and applications of organic-silica hybrid monoliths.

Organic-silica hybrid monoliths attracted attention as an alternative to extensively researched organic polymer-based and silica-based counterparts. The development and applications of these materials as extraction and separation media in capillary liquid chromatography and capillary electrochromatography were previously reviewed in several manuscripts. In this review, we will concentrate on work published since mid-2016 focusing on advances in their development using sol-gel chemistry of tetra- and trialkoxysilanes and subsequent surface modification with organic monomers, and "one-pot" strategy incorporating sol-gel chemistry of alkoxysilanes and free-radical polymerization, ring-opening polymerization, or thiol-based click polymerization with organic monomers. Approaches adapted to the preparation of hybrid monoliths made with polyhedral oligomeric silsesquioxanes will be covered as well.

Enantioseparation by zeolitic imidazolate framework-8-silica hybrid monolithic column with sulfobutylether-ß-cyclodextrin as a chiral additive in capillary electrochromatography.

A zeolitic imidazolate framework (ZIF)-8-silica hybrid monolithic column was prepared by one-step sol-gel method. The stationary phase in the monolithic column was characterized by Fourier-transform infrared spectra, X-ray diffraction, thermogravimetric analysis, nitrogen adsorption/desorption, and zeta potential. The results showed that ZIF-8-silica hybrid monolithic materials had abundant functional groups, good crystallinity, large specific surface area, and good thermal stability. A capillary electrochromatography (CEC) chiral separation system was for the first time constructed with ZIF-8-silica hybrid monolithic column and sulfobutylether-ß-cyclodextrin (SBE-ß-CD) as a chiral additive and was applied to separate the selected single and mixed chiral compounds (13 natural amino acids and 5 chiral pesticides). Under the optimized CEC conditions, all the single analytes achieved baseline separation with resolution of 2.14-5.94 and selectivity factor of 1.06-1.49 in less than 6 min, and the mixed amino acids with similar properties were also simultaneously enantioseparated (Rs ≥ 1.82). Relative standard deviations (RSDs) of migration time and column efficiency were lower than 4.26% and did not change significantly after 200 runs, evidencing excellent reproducibility and stability. These results demonstrate that the application of SBE-ß-CD as a chiral additive for ZIF-8-silica hybrid monolithic columns is a promising method for the separation of chiral compounds.