In situ fabrication of 3D COF-300 in a capillary for separation of aromatic compounds by open-tubular capillary electrochromatography

Asymmetric catalytic synthesis of chiral covalent organic framework composite (S)-DTP-COF@SiO2 for HPLC enantioseparations by normal-phase and reversed-phase chromatographic modes

A novel CCOF core-shell composite material (S)-DTP-COF@SiO2 was prepared via asymmetric catalytic and in situ growth strategy. The prepared (S)-DTP-COF@SiO2 was utilized as separation medium for HPLC enantioseparation using normal-phase and reversed-phase chromatographic modes, which displays excellent chiral separation performance for alcohols, esters, ketones, and epoxides, etc. Compared with chiral commercial chromatographic columns (Chiralpak AD-H and Chiralcel OD-H columns) and some previously reported chiral CCOF@SiO2 (CC-MP CCTF@SiO2 and MDI-β-CD-modified COF@SiO2)-packed columns, there are 4, 3, 13, and 15 tested racemic compounds that could not be resolved on the Chiralpak AD-H column, Chiralcel OD-H column, CC-MP CCTF@SiO2 column, and MDI-β-CD-modified COF@SiO2 column, respectively, which indicates that the resolution effect of (S)-DTP-COF@SiO2-packed column can be complementary to the other ones. The effects of the analyte mass, column temperature, and mobile phase composition on the enantiomeric separation were investigated. The chiral column exhibits good reproducibility after multiple consecutive injections. The RSDs (n = 5) of the peak area and retention time were less than 1.5% for repetitive separation of 2-methoxy-2-phenylethanol and 1-phenyl-1-pentanol. The chiral core-shell composite (S)-DTP-COF@SiO2 exhibited good enantiomeric separation performance, which not only demonstrates its potential as a novel CSP material in HPLC but also expands the range of applications for chiral COFs.

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 %.

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.

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.

Three-dimensional fluorinated covalent organic frameworks coated capillary for the separation of fluoroquinolones by capillary electrochromatography

In this work, a three-dimensional fluorinated covalent organic frameworks (3D FCOFs) JUC-515 was synthesized from tetra(4-aminophenyl)methane (TAM) and 2,3,5,6-tetrafluoroterephthalol (TFA) by an ionic liquid method. JUC-515 was introduced into the capillary column and bonded to the inner wall of the capillary column by chemical bonding. Through a variety of characterization results, JUC-515 was successfully synthesized and introduced into the capillary column. The effects of buffer solution concentration, organic additive content and pH of the buffer solution on the separation of fluoroquinolones (FQs) were investigated in detail. The JUC-515-coated capillary column showed good resolution (>1.5) and reproducibility. The relative standard deviations (RSDs) of the retention time for intraday, interday, column-to-column and interbatch precision were less than 0.88%, 2.45%, 2.74% and 3.32%, respectively. The RSDs of the peak area for intraday, interday, column-to-column and interbatch precision were less than 3.79%, 4.31%, 3.33% and 5.62%, respectively. The JUC-515-coated capillary column could be used no less than 150 times. The results showed that the JUC-515-coated capillary column had good separation performance. In addition, by separating fluorinated β-phenylalanine analogs, β-phenylalanine and trifluoromethyl β-phenylalanine analogs, the separation mechanism based on fluorine interactions was discussed. In conclusion, JUC-515 had good potential as a stationary phase for capillary electrochromatography.

Adsorption Performance of Magnetic Covalent Organic Framework Composites for Bisphenol A and Ibuprofen

As typical environmental endocrine disruptors and nonsteroidal anti-inflammatory drugs, bisphenol A and ibuprofen in water supplies can cause great harm to the ecological environment and human health. In this study, magnetic covalent organic framework composites Fe₃O₄@COF-300 were synthesized by the hydrothermal method and used to remove bisphenol A and ibuprofen from water. Fe₃O₄@COF-300 could be rapidly separated from the matrix by external magnetic fields, and could selectively adsorb bisphenol A and ibuprofen in the presence of coexisting compounds such as phenol, Congo red, and amino black 10B. The removal efficiency of ibuprofen was 96.12-98.52% at pH in the range of 2-4 and that of bisphenol A was 92.18-95.62% at pH in the range of 2-10. The adsorption of bisphenol A and ibuprofen followed a pseudo-second-order kinetic and Langmuir model, and was a spontaneous endothermic process with the maximum adsorption amounts of 173.31 and 303.03 mg∙g^-1, respectively. The material presented favorable stability and reusability, and the removal efficiency of bisphenol A and ibuprofen after 5 cycles was still over 92.15% and 89.29%, respectively. Therefore, the prepared composite Fe₃O₄@COF-300 exhibited good performance in the adsorption of bisphenol A and ibuprofen in water.

In situ growth of imine-based covalent organic framework as stationary phase for high-efficiency electrochromatographic separation

Design of the smart stationary phases, which can improve the separation efficiency is an essential work in the capillary electrochromatography (CEC). Owing to good excellent properties, covalent organic frameworks (COFs) have showed promising potential in the area of separation science. Here, a micro- and mesoporous COF TAPB-BTCA with adequate available interaction sites and outstanding mass transfer performance was first exploited as a stationary phase for high-efficiency in capillary electrochromatography. Through in situ growth approach, the COF TAPB-BTCA coated capillary column was facilely prepared at room temperature. The separation ability of the COF TAPB-BTCA coated capillary column was studied. The fabricated column showed high efficiency for the separation of six types of small molecular compounds, including alkylbenzenes, chlorobenzenes, phenols, parabens, vanillin and related phenolic compounds, and non-steroidal anti-inflammatory drugs (NSAIDs). The maximum theoretical plates reached up to 293,363 N/m for phloroglucinol, showing significantly improved column efficiency in comparison to previous reported COFs-based columns. In addition, the mass loadability for methylbenzene was achieved to 1.44 mg/mL. Also, excellent reproducibility and stability were obtained on the COF TAPB-BTCA coated columns. The relative standard deviations of intra-day (n = 3), inter-day (n = 3) and three batch tubes were all less than 2%, and no obvious change was presented in separation performance after the column was used 120 runs. This COF TAPB-BTCA-based stationary phase would be a promising candidate for high-efficiency chromatographic separation.

Recent applications and chiral separation developments based on stationary phases in open tubular capillary electrochromatography (2019–2022)

Capillary electrochromatography (CEC) plays a significant role in chiral separation via the double separation principle, partition coefficient difference between the two phases, and electroosmotic flow-driven separation. Given the distinct properties of the inner wall stationary phase (SP), the separation ability of each SP differs from one another. Particularly, it provides large room for promising applications of open tubular capillary electrochromatography (OT-CEC). We divided the OT-CEC SPs developed over the past four years into six types: ionic liquids, nanoparticle materials, microporous materials, biomaterials, non-nanopolymers, and others, to mainly introduce their characteristics in chiral drug separation. There also added a few classic SPs that occurred within ten years as supplements to enrich the features of each SP. Additionally, we discuss their applications in metabolomics, food, cosmetics, environment, and biology as analytes in addition to chiral drugs. OT-CEC plays an increasingly significant role in chiral separation and may promote the development of capillary electrophoresis (CE) combined with other instruments in recent years, such as CE with mass spectrometry (CE/MS) and CE with ultraviolet light detector (CE/UV).

Three-Dimensional Covalent Organic Frameworks: From Synthesis to Applications

Three-dimensional covalent organic frameworks (3D COFs) with spatially periodic networks demonstrate significant advantages over their 2D counterparts, including enhanced specific surface areas, interconnected channels, and more sufficiently exposed active sites. Nevertheless, research on these materials has met an impasse due to serious problems in crystallization and stability, which must be solved for practical applications. In this Minireview, we first summarize some strategies for preparing functional 3D COFs, including crystallization techniques and functionalization methods. Hereafter, applications of these functional materials are presented, covering adsorption, separation, catalysis, fluorescence, sensing, and batteries. Finally, the future challenges and perspectives for the development of 3D COFs are discussed.

β-Cyclodextrin covalent organic framework supported by polydopamine as stationary phases for electrochromatographic enantioseparation

In this work, a new open-tubular capillary electrochromatography (OT-CEC) column was prepared using β-cyclodextrin covalent organic framework (β-CD COF) as a stationary phase. Polydopamine was used to assist fabrication of β-CD COF on an inner wall of a fused-silica capillary. The coating layer on the capillary was characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Electroosmotic flow (EOF) was also studied to evaluate the variation of the inner wall of immobilized columns. Furthermore, the chiral separation effectiveness of the fabricated capillary column was evaluated by CEC using enantiomers of several related proton pump inhibitors as model analytes, including omeprazole, lansoprazole, pantoprazole and tenatoprazole. The effects of bonding time and concentration of β-CD COF, the type, concentration and pH of buffer, applied voltage were investigated to obtain satisfactory enantioselectivity. In the optimum conditions, the enantiomers of four analytes were resolved within 15 min with resolutions of 1.63-2.62. The relative standard deviation values for migration times and resolutions of the analytes representing intraday and interday were less than 6.75% and 4.24%, respectively. The results reveal that β-CD COF has great potential as chiral-stationary phases for enantioseparation in CEC.

Open Tubular Column Immobilized with Covalent Organic Frameworks for Rapid Separation of Small Molecular Compounds by Capillary Electrochromatography

Preparation of a novel TpBD (synthesized from phloroglucinol and benzidine) covalent organic framework (COF) immobilized open-tubular (OT) capillary is described by in situ growth strategy. The stationary phase in the column was characterized by Fourier transform infrared (FTIR) spectra, X-ray diffraction (XRD), thermogravimetric analysis (TGA), nitrogen adsorption–desorption isotherms, scanning electron microscope (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectrum (EDS). Several families of compounds with different properties (alkylbenzenes, parabens, sulfonamides and benzoic acids) were selected to evaluate the performance of the TpBD COF immobilized capillary. The results showed that the stationary phase was uniform with about 6.0 μm thickness under the optimal preparation conditions, and the relative standard deviations (RSDs) were no more than 3.13% of alkylbenzenes on the TpBD COF immobilized capillary for 11 consecutive runs, which exhibited its excellent reproducibility and stability. A rapid baseline separation of each family of the analytes (neutral parabens, amphoteric sulfonamides and acidic benzoic acids) was obtained in less than 6 min with a resolution (Rs) of 2.79~9.30, which sufficiently verified the rapid separation, high resolution and wide application range of the TpBD COF immobilized capillary, and further revealed this strategy of fabricating COF to capillary column to show great promise in capillary electrochromatography.

Single-Crystalline Covalent Organic Frameworks as High-Performance Liquid Chromatographic Stationary Phases for Positional Isomer Separation

Vigorously developing new stationary phases to meet the requirements for the separation of positional isomers that have similar physicochemical properties is still an urgent topic in separation science. Herein, a single-crystalline covalent organic framework (COF-300) packed column for the separation of positional isomers in high-performance liquid chromatography (HPLC) was reported for the first time. Benefitting from its regular shape, excellent chemical and thermal stability, microporous feature, and strong hydrophobicity of single-crystalline COF-300, the single-crystalline COF-300-packed column showed excellent resolution for the separation of positional isomers, including nitroaniline, dichlorobenzene, dibromobenzene, diiodobenzene, diethylbenzene, chloronitrobenzene, bromonitrobenzene, and iodonitrobenzene isomers, which cannot be all separated on commercial columns and a polycrystalline COF-300-packed column. Especially, the resolution values for m-/p-diiodobenzene and o-/m-diiodobenzene were 4.45 and 2.53. Moreover, the alkylbenzene, monosubstituted aromatics, polycyclic aromatic hydrocarbons, and the mixture of ethylbenzene and styrene were also baseline separated on the single-crystalline COF-300-packed column. This successful application not only confirmed the great potential of single-crystalline COFs in HPLC separation of positional isomers but also pioneered the utilization of single-crystalline COFs in separation science.

A covalent organic framework for chiral capillary electrochromatography using a cyclodextrin mobile phase additive

Covalent organic frameworks (COFs) have been recognized as promising solid phases in capillary electrochromatography (CEC). Imine-based COF-coated open-tubular CEC column (COF TpBD-coated OT column) was prepared and characterized by X-ray diffraction (XRD), Fourier-transform infrared (FT-IR) spectra, thermogravimetric analysis (TGA), nitrogen adsorption/desorption (Brunauer-Emmett-Teller [BET]), and scanning electron microscopy (SEM). The results showed that the column efficiency was up to 26,776 plate/m, and the thickness of stationary phase was about 6.00 μm for the column prepared under the optimal conditions. Enantioseparation of 15 kinds of the single chiral compounds (histidine, arginine, lysine, leucine, threonine, methionine, valine, aspartic acid and glutamic acid, fipronil, diclofop, imazamox, quizalofop-p, imazethapyr, and acephate) and 3 kinds of mixed amino acids racemaces (valine, methionine, and glutamic acid) were performed with three methods: capillary electrochromatography with COF TpBD-coated OT column (Method 1), CEC with COF TpBD-coated OT column as the separation channels, and capillary electrophoresis (CE) with HP-β-CD as the chiral mobile phase additive (Method 2) and CE with HP-β-CD as the chiral mobile phase additive (Method 3). Separation efficiency and chiral selectivity of Method 2 was best among the three methods. Under the optimal separation conditions of Method 2, all the enantiomers reached the baseline separation regardless of the single chiral compounds or the mixed amino acids. Relative standard deviation (RSDs) of the mean column efficiency for reproducibility and stability was in the range of 0.46-1.49%. This combination of CEC and CE has great potential for use in chiral separation.

Synthesis of a covalent organic framework with hydrazine linkages and its application in open-tubular capillary electrochromatography

Recently, covalent organic frameworks (COFs), owning to their excellent and unique properties, are attracting the attention of numerous researchers in some areas, especially the domain of chromatographic separation. However, the application of hydrazine linkages COFs in open-tubular capillary electrochromatography (OT-CEC) lies in the early stage at present. Herein, a well-crystallized hydrazine-linked COF (Tf-DHzOH) was synthesized successfully from 2,5-dihydroxyterephtalohydrazide and 1,3,5-triformyl-benzene. Tf-DHzOH was firstly regarded as a stationary phase material to prepare the Tf-DHzOH coated capillaries with different coating thickness by covalent bonding in this work. The characterization results showed that Tf-DHzOH was successfully synthesized. The separation performance and stability of the Tf-DHzOH coated capillary were evaluated by considering amino acids, sulfonamides, tetracyclines and benzene compounds as analytes. The relative standard deviations (RSDs) of separation time in the intra-day (n = 9), inter-day (n = 6), column-to-column (n = 3) and batch-to-batch (n = 3) were 0.76-4.97%, 1.59-5.94%1.78-8.72% and 1.66%-8.23%, respectively, the RSDs of peak areas were 1.90-5.16%, 1.73-5.24%, 1.26-7.33% and 3.77%-11.24%, respectively. It was confirmed that there was no visible change of separation efficiency after the Tf-DHzOH-coated capillary was used more than 200 runs. The results make clear that 2D hydrazine-linked COF (Tf-DHzOH) has superior potential as the stationary phase in OT-CEC for chromatographic separation.

Capillary coated with three-dimensional covalent organic frameworks for separation of fluoroquinolones by open-tubular capillary electrochromatography

The Schiff-base reaction of 1,3,5-triformylphloroglucinol (Tp) and tetra(4-aminophenyl)methane (TAM) was performed for the synthesis of a three-dimensional covalent organic framework named 3D TpTAM, which was obtained by an ultrasound-assisted method for the first time. The morphology and structure of the synthesized TpTAM were characterized through various methods. Then, TpTAM-coated capillary columns were subsequently prepared by a covalent bonding method within a short time and applied for the separation of fluoroquinolones by capillary electrochromatography (CEC) with good resolution and reproducibility. The intraday relative standard deviations (RSDs) of the retention time and peak areas were 0.88%-0.95% and 2.27%-3.81%, respectively. The interday RSDs of retention time and peak areas were 0.71%-0.89% and 0.88%-3.60%, respectively. The column-to-column RSDs of retention time and peak areas were less than 1.90% and 13.56%, respectively. The interbatch RSDs of retention time and peak areas were less than 3.48% and 3.89%, respectively. The TpTAM-coated capillary columns could be used for no less than 100 runs with no observable changes in the separation efficiency. The separation mechanism was also studied, which indicated that π-π stacking effects, hydrophobic interactions and hydrogen bonding were the main factors. The results revealed that 3D TpTAM should have superior potential as the stationary phase in CEC for chromatographic separation.

In-situ growth of a spherical vinyl-functionalized covalent organic framework as stationary phase for capillary electrochromatography-mass spectrometry analysis

Column technology is an important part in capillary electrochromatographic science. Developing novel stationary phase with high separation efficiency and high loading capacity is an essential work. In this work, a novel spherical vinyl-functionalized covalent-organic framework (COF-V) was synthesized at room temperature and firstly employed as stationary phase for CEC-MS analysis. The COF-V based CEC column was characterized by scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The results proved the successful modification of COF-V. The COF-V based column possesses the advantages like strong electroosmotic flow, high separation efficiency and high loading capacity. The CEC column showed powerful separation selectivity to several kinds of compounds, and the highest column efficiency (theoretical plates, N) was over 1.4 × 10⁵ plates·m^-1 for methylbenzene. Besides, the COF-V modified column exhibited excellent repeatability and stability. The relative standard deviations (RSDs) of retention times for intra-day (n = 5), inter-day (n = 3) runs and column-to-column (n = 3) were all less than 2.1%. Hence, the COF-V modified column was successfully applied in CEC-MS for determination of antiepileptic drug, triazine herbicides and active ingredients in traditional Chinese medicine.

Theoretical electronic circular dichroism investigations of chiral amino acids and development of separation and identification methods independent of standards

Through an appropriate computational protocol and environmental simulation, a satisfactory fit was observed for the theoretical electronic circular dichroism (ECD) spectra of 19 chiral amino acids (AAs), which correspondeds to the forms of the AAs in aqueous solution. Methods for enantioseparation of these chiral AAs by capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC) were developed. Combining ECD with chromatographic separation methods, enantiomers were identified and quantified independent of a single enantiomer standard.

In situ room-temperature preparation of a covalent organic framework as stationary phase for high-efficiency capillary electrochromatographic separation

Covalent organic frameworks (COFs), considered as a series of newly emerging porous organic materials, have been widely utilized in separation fields. Herein, a novel COF (TFPB-BD) was first employed as stationary phase for high-efficiency capillary electrochromatographic separation. Benzidine (BD) and 1,3,5-Tris-(4-formylphenyl)benzene (TFPB) were selected as organic linkers and then introduced into the aldehyde group modified capillary for the in situ growth of TFPB-BD onto the capillary inner wall at room temperature. The morphology and formation of TFPB coated capillary column were confirmed by a variety of tools including Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDS). It's interesting that the TFPB globular crystals with nanoscale were uniformly and densely modified on the capillary inner surface. Hence, the prepared column exhibited prominent separation performance for the test analytes including alkylbenzenes, chlorobenzenes and phenolic compounds with high efficiency and high resolution. The maximum column efficiency can reach about 1.8 × 10⁵ plates•m^-1. Additionally, the high resolutions of anilines, amino acids and parabens were also achieved on the TFPB modified capillary. The precisions (RSDs) of the retention times of alkylbenzenes of intra-day runs (n = 3), inter-day runs (n = 3) and parallel columns (n = 3) were all less than 2.83%. This innovative COF-based stationary phase gives great promise for the chromatographic separation field.

In situ controllable synthesis of Schiff base networks porous polymer coatings for open-tubular capillary electrochromatography

A uniform Schiff base network (SNW) film was synthesized in situ in a controllable way through continuous flow of reactants inside the capillary. The properties and application of the as-prepared capillary was investigated in capillary electrochromatography. The effects of reaction monomer concentration and reaction time on coating thickness were studied by SEM. The results show that the reaction condition has a significant influence on the morphology and thickness of the SNW films. The thickness of the film can be controlled by changing the concentration of reaction solution and reaction time. Capillaries coated under different conditions were employed to separate four nucleotides by capillary electrochromatography, which demonstrated significant variation of migration time, peak order, and separation efficiency. Analytes containing nitrogen heterocycle structures, such as nucleotides, methylimidazole isomers, and β-lactam antibiotics, were successfully separated with the prepared open-tubular columns. Under the selected separation conditions, theoretical plate number of four nucleotides is in a range 45,237-104,505 plates·m^-1, and the resolutions are 1.98-8.07. A resolution of 1.75 is obtained for methylimidazole isomers. The nucleotides in a real sample, chicken essence seasoning, were determined using the prepared capillary column with satisfactory recoveries in the range 95 to 105%.