Capillary Electrochromatography Mode Research Articles

Recent Trends in Graphene-Based Sorbents for LC Analysis of Food and Environmental Water Samples.

This review provides an overview of recent advancements in applying graphene-based materials as sorbents for liquid chromatography (LC) analysis. Graphene-based materials are promising for analytical chemistry, including applications as sorbents in liquid chromatography. These sorbents can be functionalized to produce unique extraction or stationary phases. Additionally, graphene-based sorbents can be supported in various materials and have consequently been applied to produce various devices for sample preparation. Graphene-based sorbents are employed in diverse applications, including food and environmental LC analysis. This review summarizes the application of graphene-based materials in food and environmental water analysis in the last five years (2019 to 2023). Offline and online sample preparation methods, such as dispersive solid phase microextraction, stir bar sorptive extraction, pipette tip solid phase extraction, in-tube solid-phase microextraction, and others, are reviewed. The review also summarizes the application of the columns produced with graphene-based materials in separating food and water components and contaminants. Graphene-based materials have been reported as stationary phases for LC columns. Graphene-based stationary phases have been reported in packed, monolithic, and open tubular columns and have been used in LC and capillary electrochromatography modes.

Enantioseparation of selected chiral agrochemicals by using nano-liquid chromatography and capillary electrochromatography with amylose tris(3‑chloro-5-methylphenylcarbamate) covalently immobilized onto silica

In this paper enantiomers of selected chiral agrochemicals representing various structural classes were separated by using nano-liquid chromatography (nano-LC) and capillary electrochromatography (CEC) employing a capillary column packed with silica particles containing immobilized amylose tris(3‑chloro-5-methylphenylcarbamate) (i-ADMPC) as a chiral selector (CS). Special attention was paid to peak dispersion in nano-LC and CEC instruments used in order to make comparison between these two techniques more reliable. Enantioseparations were studied utilizing methanol (MeOH) or acetonitrile-water (ACNH2O), both containing 5 mM of ammonium acetate as the mobile phases (MPs). The tested chiral stationary phase (CSP), containing 20% (w/w) of the neutral CS onto native silica, allowed the generation of sufficiently strong electroosmotic flow (EOF) to observe separation of enantiomers of studied agrochemicals in a reasonable time also in CEC mode. Modestly higher efficiencies and enantioresolutions were obtained in CEC than in nano-LC. Just a moderate preference of CEC over nano-LC in this particular study can be explained with a significant mass transfer resistance through the CSP that is caused due to high content of the CS in CSP.

MIL-53-based homochiral metal-organic framework as a stationary phase for open-tubular capillary electrochromatography

Homochiral metal-organic frameworks (MOFs) have attracted considerable attention in many fields of research, such as chiral catalysis and chiral chromatography. However, only few homochiral MOFs can be effectively used in capillary electrochromatography (CEC) and their performances are far from adequate. In this study, we successfully synthesized achiral nanocrystalline MIL-53. A facile post-synthetic modification strategy was then implemented to functionalize the product, yielding a homochiral MOF: l-His-NH-MIL-53. This MOF was then employed as a chiral coating in open-tubular CEC mode (OT-CEC), and, as such, it exhibited high enantioselectivities for several racemic drugs. The homochiral MOF and the fabricated capillary coating were systematically characterized using transmission electron microscopy, scanning electron microscopy (with energy-dispersive X-ray spectrometry), Fourier-transform infrared spectroscopy, X-ray diffractometry, thermogravimetric analysis, circular dichroism spectroscopy, Brunauer-Emmett-Teller surface area measurements, and X-ray photoelectron spectroscopy. This study is expected to provide a new strategy for the design and establishment of MOF-based chiral OT-CEC systems.

Bilayer capillary coatings based on nanosized ion-exchangers for the capillary electrochromatography analyses of biogenic amines and amino acids

Nanoparticles are widely used in capillary electrophoresis as stationary phases adsorbed on the internal capillary walls for the separation and concentration of analytes in capillary electrochromatography. The fastest and simplest approach for the formation of coatings is a physical adsorption of nanoparticles. Nevertheless, the formed coatings frequently possess low stability. The layer-by-layer approach for the formation of stabile and dense coating of internal capillary walls based on negatively charged nanosized cation-exchanger was proposed. The method included the sequential alteration of appositively charged layers of nanosized ion-exchangers. The proposed “anion-exchanger – cation-exchanger” bilayer coating possesses high stability in wide pH range (2-10) and provides up to 120 analyses without the need of re-coating. The coating was applied for the separation and on-line concentration of catecholamines and amino acids in capillary electrochromatography mode. High efficiencies were achieved (N = 450-720 th. t.p./m and N = 400-520 th. t.p./m for cathecholamies and amino acids, respectively), while the analysis time was significantly decreased. It was established, that high concentration of negatively charged functional groups on the capillary surface led to the increase of stacking efficiency factors due to the interactions between analytes and functional groups of the modifier on the capillary walls. It contributed to the 2-4 times reduced detection limits (LODs) of analytes compared to the mono-layer coatings (LODs of catecholamines = 3-4 ng/mL, LODs of amino acids = 40-100 ng/mL).

Preparation of a two-dimensional azine-linked covalent organic framework-coated capillary and its application to the separation of nitrophenol environmental endocrine disruptors by open-tubular capillary electrochromatography

As a class of new porous crystalline materials, covalent organic frameworks (COFs) are attracting the attention of a large number of scientists. Because of their large specific surface area, low density, high stability, and tunable pore size, COFs have been widely applied in many fields, including analytical chemistry. Open-tubular capillary electrochromatography (OT-CEC) is a mode of capillary electrochromatography. In recent years, a variety of materials such as porous organic frameworks have been used as the stationary phase for OT-CEC to overcome the disadvantages of low phase ratio and column capacity, thereby improving the separation efficiency. However, there are a few reports on the use of COFs as the stationary phase to improve the separation efficiency of OT-CEC. Environmental endocrine disruptors (EEDs) are a large class of exogenous chemicals that can disturb the effect of the normal endocrine substances and adversely affect the endocrine and reproductive systems of human beings. Considering the widespread existence of EEDs and the disadvantages of existing detection methods (e. g., gas chromatography-mass spectrometry and high performance liquid chromatography-mass spectrometry), such as complicated operation and large sample consumption, it is necessary to develop new methods for the separation and determination of EEDs in complex samples. OT-CEC is a good choice in this regard because of its low sample dosage, simple operation, and high analytical speed. Accordingly, a two-dimensional azine-linked covalent organic framework (ACOF-1) with a large surface area and small pore size was synthesized according to the reference method. Then, an ACOF-1-coated capillary was fabricated using ACOF-1 as the stationary phase, via covalent bonding, and used as the separation channel to establish a new OT-CEC method for the separation and detection of nitrophenol EEDs. X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM) were used to characterize the synthesized ACOF-1 and the ACOF-1-coated capillary. The peak pattern in the XRD spectrum confirmed the successful synthesis of ACOF-1. The absorption peaks in the FT-IR spectrum and the morphology of the inner wall seen in the SEM images also demonstrated that the ACOF-1-coated capillary was fabricated successfully. A series of experiments were carried out to investigate the effects of the organic additive (methanol) content, pH, and concentration of the borate buffer on the resolution, migration time, and peak shape. Based on the results, the optimal separation conditions for the four nitrophenol analytes were 15 mmol/L borate (pH 9.20) with 10% (v/v) methanol. Under the optimum conditions, 2-nitrophenol (2-NP), 4-nitrophenol (4-NP), 2,4-dinitrophenol (DNP), and 2,4,6-trinitrophenol (TNP) could be baseline separated within 20 min by the established OT-CEC method. The linear range for 2-NP and 4-NP was 10-500 mg/L, while that for DNP and TNP was 20-1000 mg/L. The determination coefficients (R2) were greater than 0.99. For the four analytes, the limits of detection and limits of quantitation were in the ranges of 0.13-0.23 mg/L and 0.45-0.60 mg/L, respectively. The intraday, interday, and column-to-column relative standard deviations (RSDs) of the migration time and peak area were less than 9.4%. These results revealed that the established method has good repeatability and high stability, thus being suitable for the separation and detection of nitrophenol EEDs. The mechanism studies revealed that the pore size of ACOF-1 was the main factor influencing the separation behavior of each analyte. This work demonstrated the feasibility of using capillary electrochromatography with COFs as the stationary phase for the separation and detection of EEDs. Future research will continue to focus on the preparation of COF-coated capillaries and their application to OT-CEC separation and determination of EEDs.

Front cover: Performance of laterally elongated pillar array columns in capillary electrochromatography mode

Front cover: Performance of laterally elongated pillar array columns in capillary electrochromatography mode

Performance of laterally elongated pillar array columns in capillary electrochromatography mode.

In the present study, cylindrical and laterally elongated pillar array columns were investigated for use in capillary electrochromatography. Minimal theoretical plate heights of H = 1.90 and 1.46μm (in absence of sidewall effect) were obtained for coumarin C440 under unretained conditions for cylindrical and rectangular (laterally elongated, aspect ratio 4) pillar array columns, respectively. By comparing dispersion at the entire channel width to that at the central zone only, it appears that sidewall related dispersion significantly contributes to overall dispersion. A 40% reduction of the plate height was observed by taking into account only the central channel zone. A kinetic plot analysis was performed to evaluate the potential of the studied geometries by considering a maximum operating voltage of 20kV as limiting parameter. It was demonstrated that rectangular radially elongated pillars produce a higher efficiency than cylindrical pillars and other microfabricated column structures for microchip capillary electrochromatography previously studied.

A monolithic capillary modified with a copoplymer prepared from the ionic liquid 1-vinyl-3-octylimidazolium bromide and styrene for electrochromatography of alkylbenzenes, polycyclic aromatic hydrocarbons, proteins and amino acids.

A monolithic capillary column was prepared by single-step copolymerization of the ionic liquid 1-vinyl-3-octylimidazolium bromide (VOI) and styrene. The VOI and styrene monomers were introduced to provide multiple interaction sites and increase hydrophobicity and aromaticity of the monolithic column, respectively. The effect of porogen ratio, monomer ratio and reaction temperature on permeability was investigated. The resulting column was characterized by scanning electron microscopy, and the results suggest that the column possesses high porosity and good homogeneity. A relatively strong anodic electroosmotic flow was generated over a wide range of pH values (pH2.0-10.0), and this facilitates the rapid separation of analytes within 12min. Alkylbenzenes, polycyclic aromatic hydrocarbons (PAHs), proteins and amino acids were used to evaluate the performance of the monolithic column under capillary electrochromatography mode by UV detection. Mixed-mode retention mechanisms including hydrophobic interaction, π-stacking, ion-exclusion interaction were observed. The monolithic column exhibits high column efficiency (8.72 × 104 plates∙m-1) and satisfying separation capability (the resolution of four alkylbenzenes: 2.54, 2.86 and 4.62, four PAHs: 2.79, 4.83 and 4.77, three proteins: 4.35 and 2.86, two amino acids: 3.34). Graphical abstractSchematic representation of capillary electrochromatography (CEC) systems with ionic liquid and styrene based organic polymer monolithic column for separation of alkylbenzenes, polycyclic aromatic hydrocarbons, proteins and amino acids.

Temperature effects on retention and efficiency of butyl and lauryl acrylate porous polymer monoliths in capillary electrochromatography.

The development of organic porous polymer monoliths represents an alternative approach to stationary phase design. The use of these materials has helped to rekindle interest in capillary electrochromatography. Although a large number of investigations have explored different monolith recipes, polymerization conditions, and application challenges, few investigations have addressed the fundamentals of this separation mode with this type of material. This study addresses the thermodynamics of the reversed phase retention mechanism on 100% butyl acrylate and 1:3 butyl:lauryl acrylate (volume/volume ratio) porous polymer monoliths used in a capillary electrochromatography mode. Linear van't Hoff plots yield enthalpies of retention of -3.9 to -14.3kJ/mol on two different, but related columns for five selected hydrophobic analytes across a thirty degree temperature range. Minimum plate heights were only moderately impacted over this temperature range.

Comparative study on enantiomer resolving ability of amylose tris(3-chloro-5-methylphenylcarbamate) covalently immobilized onto silica in nano-liquid chromatography and capillary electrochromatography

In the present study separation of enantiomers of some chiral neutral and weakly acidic analytes was investigated on the chiral stationary phase (CSP) made by covalent immobilization of amylose tris(3-chloro-5-methylphenylcarbamate) onto silica in nano-liquid chromatography (nano-LC) and capillary electrochromatography (CEC) in acetonitrile and aqueous acetonitrile. Few comparisons were made also between the enantioseparations in nano-LC and high-performance liquid chromatography (HPLC) with the chiral column of 4.6 × 250 mm dimension. Slightly better separation of enantiomers was observed in HPLC mode compared to nano-LC mode. It was shown that in the capillary columns packed with the CSP containing about 20% (w/w) of a covalently immobilized neutral chiral selector, amylose tris(3-chloro-5-methylphenylcarbamate), sufficient electroosmotic flow has been generated and enantioseparations with reasonable analysis time were performed also in CEC mode. It was shown once again that CEC offers a clear advantage over nano-LC from the viewpoint of plate numbers and peak resolution.

Open tubular capillary column of 50μm internal diameter with a very high separation efficiency for the separation of peptides in CEC and LC.

A specially designed long open tubular capillary column (50μm internal diameter and 112cm effective length) was prepared by fabrication of a thin three-component co-polymer layer on the inner surface of silica capillary. A pretreated silica capillary was reacted with 4-(chloromethyl)phenyl isocyanate in the presence of dibutyltin dichloride as catalyst followed by sodium diethyl dithiocarbamate. Then a thin polymer layer was made on the inner surface of capillary by reversible addition-fragmentation transfer polymerization of styrene, N-phenylacrylamide, and methacrylic acid. A carefully adjusted formulation of reaction mixture and elaborated procedures were adopted to secure formation of the co-polymer layer of enhanced separation performance. The co-polymer immobilized open tubular capillary column was used for the separation of a synthetic mixture of five peptides and excellent separation efficiency (over 1.7 million per column) was obtained in the capillary electrochromatography mode. Such excellent separation efficiencies of ca. 1m column have not been obtained in the isocratic elution mode so far. The column was also used for separation of the peptides in the liquid chromatography mode to show very good separation efficiency (average 286 700 per column).

Development of Amine Capillary Column Applied to the Analysis of Basic Compounds by Electrochromatography

An amine capillary column was developed in a fused-silica capillary as stationary phase and applied to separation of basic compounds by capillary electrochromatography (CEC). The functionalized capillary was prepared by inmobilization of 3-Aminopropyl)triethoxysilane (APTES). The CEC conditions including APTES and buffer concentration, pH and applied voltage were investigated to obtain the optimal CEC system for the separation of three anesthetics as basic test molecules. The capillary column provided an efficiency of up to 20,000 plates/m. Lidocaine, ketamine and xilacine were baseline separated under the running conditions with 10 mM Na2HPO4 pH 9.0 as BGE. The applied voltage was 5 kV temperature was set at 25oC and UV detection was performed. The resolutions were 4.97 and 1.53 for ketamine, lidocaine and xilacine, respectively. The column used in CEC mode showed better separation of the anesthetics compared with those used in the capillary zone mode. The comparison with reversed stationary phases used in HPLC in terms of resolution (Rs), sensitivity (LOD), efficiency (N), precision (RSD), asymmetry (T) was also performed. This study provided an alternative way for the CEC separation of basic compounds and demonstrated the improvement in the chromatographic parameters.

Supermacroporous polymer monolith prepared with polymeric porogens via viscoelastic phase separation for capillary electrochromatography

Supermacroporous poly(methacrylic acid-butyl methacrylate-ethylene glycol dimethacrylate) monoliths with the pore size up to 5–10μm were successfully prepared in a ternary polymeric porogens utilizing viscoelastic effect. High concentration (over 20mg/mL) of polystyrene (PS) in porogen was used to achieve the desirable characteristics of the monolithic capillary. Modification of the co-porogen composition, i.e., the content of dimethyl sulfoxide and isooctane, enabled tailoring of the supermacropore structure with a wide range of pore size. The effects of the amount of polymer porogen and molecular weights of PS on the formation of supermacropore were also studied. In preliminary applications, the separations of alkyl phenones and alkylbenzenes were achieved on the supermacropore columns using a mode of capillary electrochromatography. The study demonstrated successfully the ability of polymer porogen to form supermacropore monolith via viscoelastic phase separation

Facile preparation of organic-inorganic hybrid polymeric ionic liquid monolithic column with a one-pot process for protein separation in capillary electrochromatography.

An organic-inorganic hybrid monolithic column based on 1-vinyl-3-dodecylimidazolium bromide (VC12Im(+)Br(-)) has been prepared in a single step by combining radical copolymerization with a non-hydrolytic sol-gel (NHSG) process. The NHSG process was significantly shortened to 6h by using formic acid as catalyst. For comparison, we also prepared polymeric ionic liquid (PIL) monolithic columns by hydrolytic sol-gel and organic polymeric process, respectively. The resulting monolithic columns were characterized by Fourier transform infrared spectra, scanning electron microscopy, and Brunauer-Emmett-Teller. Under the capillary electrochromatography mode, these columns were applied to separate alkylbenzenes, anilines, and proteins, respectively. The results indicated that the NHSG-based hybrid PIL monolithic column exhibited the highest column efficiency among the three types of columns; organic solvent, commonly required by the traditional columns to achieve satisfactory separation efficiency for proteins, was absent in the NHSG-based hybrid PIL monolithic column because of the biocompatibility of the VC12Im(+)Br(-), which was beneficial to analysis of protein containing samples. In order to demonstrate its application potential, the developed NHSG-based hybrid PIL monolithic column was also employed to separate egg white sample.

Polymethacrylate monoliths with immobilized poly-3-mercaptopropyl methylsiloxane film for high-coverage surface functionalization by thiol-ene click reaction

In this work, new polythiol-functionalized macroporous monolithic polymethacrylate-polysiloxane composite materials are presented which can be useful substrates for highly efficient immobilization of (chiral) catalysts, chromatographic ligands, and other functional moieties by thiol-ene click reaction. Poly(glycidyl methacrylate-co-ethylene dimethacrylate) (poly(GMA-co-EDMA)) monoliths were coated with a poly-3-mercaptopropyl methylsiloxane (PMPMS) film and subsequently the polymer was covalently immobilized by formation of crosslinks via nucleophilic substitution reaction with pendent 2,3-epoxypropyl groups on the monolith surface. This monolith, though, showed similar levels of surface coverage as a reference monolith obtained by opening of the epoxide groups with sodium hydrogen sulfide. However, a 3-step functionalization by amination of the epoxy monolith, followed by its vinylation with allylglycidyl ether and subsequent thiolation by coating of a thin polythiol (PMPMS) film and crosslinking by click reaction furnished a monolith with more than 2-fold elevated thiol coverage. Its further functionalization with a clickable chiral quinine carbamate selector clearly documented the benefit of highly dense thiol surfaces for such reactions and synthesis of functional materials with proper ligand loadings. The new monoliths were chromatographically tested in capillary electrochromatography mode using N-3,5-dinitrobenzoyl-leucine as chiral probe and the capillary column with the monolith having the highest selector coverage, produced from the precursor with the most thiols on the surface, showed the largest separation factor. By performic acid oxidation the surface characteristic could be tuned and strongly altered due to a delicate balance of enantioselective and non-specific interactions.

Monolithic Column and Coating Capillary Based on Molecularly Imprinted Polymers for Separation of Organic Compounds in Capillary Electrochromatography

Molecular imprinting is a powerful technique to form a synthetic polymer receptor with tailor-made binding sites. This article gives a short overview of the application of the principle of molecularly imprinted polymers (MIPs) in capillary electrochromatography (CEC). Some new developments of monolithic column and coating based on MIPs in CEC mode are presented. Lastly, the review also discusses their applications for separation of organic compounds and future perspectives in this field. Keywords: Molecularly imprinted polymers, Capillary electrochromatography, Monolithic column, Coating.

Poly(triallyl isocyanurate–co-ethylene dimethacrylate–co-alkyl methacrylate) stationary phases in the chromatographic separation of hydrophilic solutes

This study describes the ability of triallyl isocyanurate (TAIC)–co-methacrylate ester polymer monoliths as stationary phases for the separation of hydrophilic compounds (phenolic acids, amino acids and catecholamines) in capillary electrochromatography (CEC) and ultra high pressure liquid chromatography (UHPLC). Several TAIC–co-methacrylate ester polymer monoliths prepared by single-step in situ copolymerization of TAIC, ethylene dimethacrylate (EDMA) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS), with or without alkyl methacrylates were characterized by examining the SEM image, surface area, contact angle, and the thermal decomposition temperature. Compared to the conventional methacrylate ester-based monoliths, these proposed monoliths possessed hydrophilic character thus increased wettability which improved chromatographic separation selectivity of polar phenolic acids. Among the proposed TAIC–co-methacrylate monoliths, poly(TAIC–co-EDMA–AMPS–co-stearyl methacrylate (SMA)) showed separation selectivity with an increased analyte resolution from 0.0 to 0.92 for 4-hydroxybenzoic acid and vanillic acid, which were consistently difficult to resolve in the reversed-phase chromatographic mechanism of these monoliths in aqueous mobile phases. Moreover, stable ionization efficiencies were observed when this monolith was combined with ESI-MS detector possibly because an organic solvent-rich sheath liquid was used in the CEC–MS. This study demonstrates the potentiality of novel TAIC–co-methacrylate polymer monoliths in hydrophilic solute separation either in CEC or UHPLC mode.

Molecularly imprinted nanoparticles with nontailing peaks in capillary electrochromatography

The combination of microparticles of molecularly imprinted polymers (MIPs) with partial filling capillary electrochromatography (CEC) has previously been demonstrated for the enantiomer separation. In this paper, precipitation polymerization was used to prepare d-zopiclone imprinted nanoparticles (50–80nm) by a strategy of the dilution of pre-polymerization mixtures. The influence of some important parameters on the preparation of MIPs nanoparticles, including template to monomer ratio, type and amount of cross-linking monomer, and functional monomer composition ratio were investigated. In addition, the effect of separation condition, e.g., organic modifier content, pH value and salt concentration of buffer, on the electrochromatographic behavior of the MIP nanoparticles were studied. In spite of lower selectivity factor (1.11), high column performance (theoretical plates 41,400) of template was obtained and the resolution of enantiomers separation was 4.75 under the optimized conditions. Compared to the previously reported MIP microparticles, the MIP nanoparticles showed good peak symmetry and an ability of high speed separation (<15min) in CEC mode.

Polymethacrylate-based monolithic capillary column with weak cation exchange functionalities for capillary electrochromatography

Polymethacrylate-based monolith with weak cation exchange functionalities was prepared in capillary column (i.d. 100 μm, o.d. 375 μm) by in situ polymerization of butyl methacrylate, ethylene dimethacrylate and N-methacryloyl-L-glutamic acid in presence of porogens. The porogen mixture included N,N-dimethyl formamide and phosphate buffer. The preparation procedure of stationary phase contained the synthesis of monomer, silanization of capillary inner wall and in situ polymerization. The use of amino acid based monomer for the monolith synthesis is one of the originalities of this novel approach. N-methacryloyl-L-glutamic acid has two carboxyl functionalities. The separation of the solutes were performed at different acetonitrile/phosphate buffer and acetonitrile/sodium hydroxide contents. The applied voltage for the alkyl benzenes was changed between +5 and +30 kV. CEC separations of alkyl benzenes, acidic, basic, phenolic and some polycylic aromatic compounds were succesfully performed under capillary-electrochromatography mode with cathodic electroosmotic flow.

Preparation and evaluation of ionic liquid-gold nanoparticles functionalized silica monolithic column for capillary electrochromatography

This paper describes the development of silica monolithic column modified with ionic liquids-gold nanoparticles (ILs-GNPs) for capillary electrochromatography (CEC). The novel ILs (1-methyl-2-mercapto-3-butylimidazolium bromide) were synthesized and used to modify GNPs functionalized silica monolithic column via the formation of a Au-S bond. The morphology of the GNPs and ILs-GNPs functionalized silica (ILs-GNPs-silica) monolithic column were characterized by transmission electron microscopy and scanning electron microscope, respectively. A cathodic electroosmotic flow was observed at pH above 6.4 on ILs-GNPs-silica monolithic column, which was reversed at acidic pH. The electrochromatographic performance of ILs-GNPs-silica monolithic column was evaluated by separation of different kinds of analytes such as hydrophobic, polar and basic compounds. The ILs-GNPs-silica monolithic column displayed enhanced hydrophobic retention characteristics in the separation of five hydrophobic n-alkylbenzenes when compared to the ILs bonded silica monolithic column. The column efficiencies for the n-alkylbenzenes were from 62,000 to 110,000 N m(-1). The ILs-GNPs-silica monolithic column exhibited reversed-phase electrochromatographic behavior toward neutral solutes. Separation of polar compounds was demonstrated on ILs-GNPs-silica monolithic column in reversed-phase CEC mode using high aqueous mobile phases. The relatively good peak shape and high separation efficiency on ILs-GNPs-silica monolithic column was obtained for basic solutes when compared to silica monolithic column modified GNPs.