Electrochromatographic Separation Research Articles

Rapid polymerization of polyhedral oligomeric siloxane-based zwitterionic sulfoalkylbetaine monolithic column in ionic liquid for hydrophilic interaction capillary electrochromatography

A novel polyhedral oligomeric siloxane (POSS)-based zwitterionic monolithic capillary column was prepared via one-pot polymerization in ionic liquid porogen, using N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropyl)ammonium betaine (DMMSA) and methacrylic ethyl trimethylammonium chloride (META) as binary functional monomers, and methacryl substituted POSS as cross-linker. The pore structure, permeability and homogeneity were well tuned by optimizing the polymerization conditions. The resultant monolith was characterized by scanning electron microscopy, nitrogen adsorption/desorption isotherm and Fourier transform infrared spectroscopy. The incorporation of zwitterionic ligand (DMMSA), quaternary amine group (META) and rigid POSS skeleton endows the hybrid organic-silica monolith with high hydrophilicity, electrostatic interaction and good mechanical stability, as well as a tunable electroosmotic flow over wide pH range. A close investigation of capillary electrochromatographic separations of different types of polar compounds such as bases, nucleosides and benzoic acids on such stationary phase exhibited a retention independent column efficiency up to 118,000 plates/m (thiourea), as well as a mixed-mode hydrophilic interaction chromatography (HILIC) retention mechanism including weak electrostatic interaction, hydrophobic interaction and anion exchange.

A stationary pseudophase semi-permanent coating for open-tubular capillary liquid chromatography and electrochromatography

We describe the chromatographic and electrochromatographic separation of small neutral and charged analytes using a fused silica capillary with a stationary pseudophase semi-permanent coating of didodecyldimethyl ammonium bromide (DDAB) aggregates. The coating was prepared by flushing the capillary with a DDAB solution that was rinsed out with the mobile phase. Our studies (i.e., electroosmotic flow measurements by capillary electrophoresis, chromatographic retention of a neutral probe and atomic force microscopy) suggested the formation of DDAB patchy admicelle, complete admicelle, or larger aggregates at the solid surface - liquid interface inside the capillary, depending on the concentration of DDAB used in coating the capillary. The analytical figures of merit for open tubular liquid chromatography (OT-LC, pressure driven) and open tubular capillary electrochromatography (OT-CEC, voltage driven) using a capillary coated with 0.5 mM DDAB and mobile phase/background solution of 25 mM borate buffer at pH 9.5 with 10% MeOH were the following: LOD = 3.0–5.0 µg/mL (OT-LC) and 2.5–5.0 µg/mL (OT-CEC); linearity R2 > 0.99 (peak area (OT-LC) and corrected peak area (OT-CEC)), intraday and interday repeatability%RSD < 5% (n = 12) for retention/migration time, peak area (OT-LC) and corrected peak area (OT-CEC). The reversed-phase and anion-exchange property of the stationary pseudophase was studied by the addition of organic solvents and sodium chloride to the mobile phase, respectively. We also demonstrate the increase in the ks of the tested analytes by implementing successive multiple ionic layer (SMIL) coating strategies with DDAB in combination with a cationic and/or anionic polyelectrolyte. The use of a stationary pseudophase coating is potentially an easy alternative way to conduct open-tubular liquid chromatography and electrochromatography.

High-Efficiency and Versatile Approach To Fabricate Diverse Metal-Organic Framework Coatings on a Support Surface as Stationary Phases for Electrochromatographic Separation.

A large number of metal-organic frameworks (MOFs) have exhibited increasingly wide utilization in the field of chromatographic separation owing to their intrinsic fascinating properties. However, the previous studies on supported MOF coating-based chromatographic separation focused only on the synthesis and chromatographic performance of a certain kind of supported MOF coatings as stationary phases using the multiple-step, complicated, and time-consuming modification methods, which severely impeded the widespread application of MOFs in separation science. Herein, a high-efficiency and versatile methodology toward diverse supported MOF coating-based stationary phases to achieve high-efficiency chromatographic separation was first reported based on the immobilized cysteine (Cys)-triggered in situ growth (ICISG) strategy. As a proof-of-concept demonstration, four types of MOF crystals consisting of different ligands and metal ions (Zn2+, Cu2+, Fe3+, and Zr4+) were conveniently and firmly grown on a Cys-modified capillary using the ICISG strategy and employed as the functional stationary phase for electrochromatographic separation. A broad variety of neutral, acidic, and basic compounds were all separated in a highly efficient manner on the developed four MOF-coated columns. The maximum theoretical plate number for Cys-MIL-100(Fe)@capillary was close to 1.0 × 105 plates/m, and the intraday, interday, and column-to-column repeatabilities of retention times for the four MOF-modified columns were all less than 5.25%. More interestingly, the diversified separation performance of the developed MOF-coated columns indicated that the preparation strategy and the skeletal structure of the MOF coating-based stationary phases have a significant influence on the electrochromatographic separation performance and column capacity. Benefiting from the strong universality and high applicability of the developed ICISG strategy, the present study provides an effective route to facilitate the design and fabrication of novel functional MOF-based chromatographic stationary phases.

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.

Dendritic Mesoporous Silica Nanospheres: Toward the Ultimate Minimum Particle Size for Ultraefficient Liquid Chromatographic Separation.

Use of smaller particle size of packing materials in liquid chromatography leads to faster separation and higher efficiency. This basic law has driven the evolution of packing materials for several generations. However, the use of nanoscale packing materials has been severely hampered by extremely high back pressure. Here, we report a new possibility of solving this issue via introducing novel nanomaterials with highly favorable structures. n-Octyl-modified monodispersed dendritic mesoporous silica nanospheres (DMSNs) with an unprecedentedly small diameter (ca. 170 nm) and appropriate pore size (5.6 nm) were controllably synthesized and demonstrated to be a practically applicable packing material offering ultrahigh efficiency. The center-radial centrosymmetric mesopore channels significantly improved the permeability of packed capillaries, enabling column packing and capillary electrochromatographic separation on regular instruments. Due to the unique morphology, very tiny particle size, and highly uniform packing, the packed column exhibited ultrahigh efficiency up to 3 500 000 plates/m. Powerful separation capability was demonstrated with glycan profiling of cancerous and normal cells, which revealed that cancerous cells exhibited characteristic N-glycans. Because DMSNs with tunable particle size and mesopores can be controllably prepared, DMSNs hold great potential to be a new record toward the ultimate generation of packing materials for ultraefficient liquid chromatographic separation.

Facile synthesis and immobilization of functionalized covalent organic framework-1 for electrochromatographic separation

Inspired by the outstanding functions of 3-aminopropyltriethoxysilane (APTES), which can be used for functionalization of both covalent organic frameworks (COFs) and substrate surfaces, herein, a proof-of-concept demonstration was carried out by one-step synthesis and immobilization of COF-1 in capillary. COF-1 was grown on the inner wall of capillary using APTES, which played a triple role of catalyst, stabilizer, and connecting arm during the process. The immobilization of COF-1 on silicon surface was confirmed by scanning electron microscopy. Moreover, COF-1 modified capillary (COF-1@capillary) column exhibited excellent performance in the electrochromatographic separation of amino acids. High resolution and separation efficiency (225,378 plates/m for 4-methylbiphenyl) were successfully achieved. Separation of methylbenzene, styrene, ethylbenzene, chlorobenzene, 1,2-dichlorobenzene, 1,2,4-trichlorobenzene, 4-methylbiphenyl, naphthalene, and 4-vinylbipheny in the electro-driven mode confirmed the successful growth of COF-1 on the inner wall of capillary. The developed facile method for the immobilization of COF-1 may pave the way for further application prospects of boron-based COFs.

Nanoscale Hierarchically Micro- and Mesoporous Metal-Organic Frameworks for High-Resolution and High-Efficiency Capillary Electrochromatographic Separation.

Metal-organic frameworks (MOFs) have been widely applied in a variety of fields. However, most of the developed MOFs are micrometer scale in crystal size and contain only micropores, which will limit the mass transport and diffusion of various analytes into their internal interaction sites, severely restricting the potential of MOFs in separation science. Herein, nanoscale hierarchically porous MOFs (NHP-MOFs) were first explored as a novel MOF-based stationary phase with excellent mass transfer performance and abundant accessible interaction sites for high-performance chromatographic separation. As a proof-of-concept demonstration, the nanoscale hierarchically micro- and mesoporous UiO-66 (NHP-UiO-66) was firmly immobilized on the capillary inner surface and utilized as the porous stationary phase for high-resolution and high-efficiency electrochromatographic separation. A wide range of low-, medium-, and high-molecular-weight analytes, including substituted benzenes, chlorobenzenes, polycyclic aromatic hydrocarbons, nucleosides, polypeptides, and proteins were all separated well on a NHP-UiO-66-coated column with excellent resolution and repeatability, exhibiting significantly improved column efficiency and separation ability compared to those of a microporous UiO-66-modified column. The maximum column efficiencies for all the six kinds of analytes reached up to 1.2 × 105 plates/m, and the relative standard deviations of the migration times of substituted benzenes for intraday, interday, and column-to-column were all lower than 5.8%. These results reveal that NHP-MOFs can effectively combine the advantages of the high specific surface area of microporous MOFs and the excellent mass transfer performance and abundant accessible interaction sites of NHP materials, possessing great prospect for high-performance chromatographic separation.

β-Cyclodextrin covalent organic framework–modified organic polymer monolith as a stationary phase for combined hydrophilic and hydrophobic aqueous capillary electrochromatographic separation of small molecules

Aβ-Cyclodextrin covalent organic framework (β-CD COF) was successfully prepared under ambienttemperature with a mild chemistry strategy from heptakis(6-amino-6-deoxy)-β-cyclodextrin and terephthalaldehyde. It was embedded into the poly[(glycidyl methacrylate)-co-(ethylene dimethacrylate)] [poly(GMA-co-EDMA)] monolith and served as the β-CD COF material-incorporated monolith. The synthetic materials were characterized by field emission scanning electron microscopy, energy-dispersive X-ray mapping analysis, transmission electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and N2 adsorption-desorption isotherm. The β-CD COF material-incorporated monolith achieved baseline separation in capillary electrochromatographic separationof three amides, three amino acids, three nucleosides, four aromatic acids, and three positional isomers (withresolutionvalues of three amides, 1.75 and 1.54; three amino acids, 5.24 and 1.75; three nucleosides, 2.56 and 1.77; four aromatic acids, 6.96, 2.74, and 1.64; three positional isomers, 1.61 and 1.50). In comparison with the original monolith, the β-CD COF material-incorporated monolith shows significantly enhanced resolution for mixed molecules. The effect ofpH and concentration of buffer and applied voltage were discussed in detail. The fabricated monolith showed good stability and reproducibility (relative standard deviation (RSD) < 6.9%). Molecular modeling illuminated the interactions between the small molecules and stationary phase, and provided a sufficient theoretical basis for experimental data. Graphical abstract Schematic presentation of the preparation of β-cyclodextrin covalent organic framework (β-CD COF) material-incorporated organic polymer monolith for separating the amides, amino acids, nucleosides, aromatic acids, and positional isomers. β-CD COF materials were synthesized and incorporated into the monolith as the stationary phase. Then, the incorporated monolith was applied in the capillary electrochromatography system for separating small molecules.

Fluoro-functionalized stationary phases for electrochromatographic separation of organic fluorides

Fluorous affinity means remarkably specific interaction between highly organic fluorides. This work aims to explore the potential of fluoro-functionalized stationary phase for the separation of organic fluorides by means of fluorous-fluorous interaction. Here, by using the Michael addition strategy between 1H,1H,2H,2H-perfluorodecanethiol (PFDT) and polydopamine (PD), a novel fluoro-functionalized stationary phase was synthesized for open-tubular capillary electrochromatography (OT-CEC). The PFDT@PD was characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and X-ray Photoelectron Spectrometer (XPS). The PFDT@PD@capillary exhibited outstanding separation performance towards neutral compounds (such as alkylbenzenes and chlorobenzenes) and organic fluorides (such as fluorobenzenes and perfluoroalkyl methacrylates etc.) with high resolution and high separation efficiency by hydrophobic interaction and fluorous-fluorous interaction. In addition, the column shows good stability and reproducibility. The relative standard deviations (RSDs) of the retention time for intra-day (n = 5) and inter-day (n = 3) runs and between columns (n = 3) are less than 0.39%, 1.22% and 3.87%, respectively. This novel type of fluoro-functionalized stationary phase represents a great application potential in organic fluorides separation field.

γ-Cyclodextrin metal-organic framework supported by polydopamine as stationary phases for electrochromatographic enantioseparation

Metal-organic frameworks (MOFs) are a novel class of porous nanomaterials composed of metals and organic linkers that have been used in many fields. A novel stereoselective stationary phase for capillary electrochromatography (CEC) has been developed in this work by employing a biodegradable, easier-to-prepare and green homochiral MOFs (Cu-SD), which composed of octakis-[6-deoxy-6-(3-mercaptopropanoic sodium)]-γ-cyclodextrin (SD, sugammadex) and transition metal ion (Cu2+) supported by polydopamine as linker. The modified capillary was characterized by scanning electron microscopy (SEM), X-ray spectrometry (XRD), energy dispersive (EDS) and Fourier transform infrared spectroscopy (FT-IR). The Cu-SD modified capillary column exhibited outstanding chiral recognition separation for five Dns-DL-amino acids (the DL-forms of phenylalanine, leucine, valine, threonine, serine). In addition, the modified column showed excellent stability and reproducibility. The relative standard deviations (RSDs) of the retention time for intra-day (n = 5) and inter-day (n = 3) and between columns (n = 3) enantioseparations were less than 0.27, 1.45 and 4.88%, respectively. Conceivably, this new-type of γ-CD-MOF represents a useful chiral stationary phase in electrochromatographic separations, and it has great potential in chiral separation field.

Electrochromatographic separation of hydrophobic amino acid enantiomers by molecularly imprinted capillary columns

In the present study, the enantiomeric forms of hydrophobic amino acids (l-tryptophan, l-tyrosine, and l-phenylalanine) were separated by molecularly imprinted capillary columns (MICC) via Capillary Electrochromatography (CEC) for the first time. The monomer ratio, crosslinker ratio, template molecule ratio, the porogen ratio and type, polymerization time, and also the effect of temperature were examined to increase the permeability properties of MICC. FTIR, SEM and BET analyses were realized for the characterization of MICC. The effect of the electric field, organic solvent ratio, and pressure were carried out experimentally to determine the optimum conditions. The separation performances of MICC and the non-imprinted capillary columns (NICC) were compared electrochromatographically.

Porous polymeric monoliths: design and preparation towards environmental applications

Polymeric monoliths are porous substrates comprised of suitable monomer(s) beside a crosslinking agent and a radical initiator. The polymerization reaction may be thermally or radiation initiated in a mold. They take the shape of continuous rods or columns upon preparation. These materials are porous substrates used to overcome some deficiencies that arose from using the corresponding traditional monoliths such as ceramic and metallic ones. Increasing the efficiency of the monolith can be achieved via grafting the surface. Functional groups on the monolithic surface can be introduced to boost the performance of the monolith. Immobilizing nanoparticles; mainly the metallic ones onto the surface of the polymeric monolith enhances the efficiency of these columns and expands their application fields. Depositing the metal nanoparticles takes place via in-situ reduction of metal nanoparticles from their precursor salts or via ex-situ loading of previously prepared nanoparticles. There are various applications for polymeric monoliths; separation of proteins, small and large molecules can be mentioned. Monoliths are used in chromatographic separation applications beside catalytic implications. These monoliths represent the stationary phase. For expanding the separation application, polymeric monoliths can be applied in electrochromatographic separations. Besides, catalytic reactions can take place inside these monolithic rods.

Polydopamine-assisted immobilization of a zinc(II)-derived metal-organic cage as a stationary phase for open-tubular capillary electrochromatography.

A capillary column was modified with a soluble zinc(II)-derived metal-organic cage (MOC) [Zn2L] as the stationary phase to obtain a new coating layer for use in open-tubular capillary electrochromatography. The inner surface of the capillary was first coated with a layer of polydopamine. Then, a solution of the MOC in dichloromethane was introduced into the capillary upon which it is bonded both covalently and non-covalently. The resulting coating layer on the capillary was characterized by scanning electron microscopy and Fourier transform infrared spectroscopy. The results demonstrated the successful formation of the [Zn2L] modified open-tubular column. The column showed good separation performance towards neutral compounds (such as methylbenzene, ethylbenzene, n-propylbenzene and n-butylbenzene), acidic drugs (such as ibuprofen, ketoprofen, flurbiprofen and diclofenac sodium), food additives (such as parabens, vanillin and related phenolic compounds) and small biomolecules (such as nucleosides and nucleotide bases) by π-interaction and hydrophobic interaction. It also exhibited good precision, the relative standard deviations of the retention time for intra-day, inter-day runs and column-to-column being <1.6%, 2.8%, and 4.0%, respectively. Graphical abstract Schematic presentation of the open-tubular column modified with zinc(II)-derived metal-organic cage by polydopamine-assisted strategy onto the inner wall of capillary for electrochromatographic separations.

In-situ growth of a metal organic framework composed of zinc(II), adeninate and biphenyldicarboxylate as a stationary phase for open-tubular capillary electrochromatography.

This work reportson the in-situ growth of a metal organic framework (MOF) composed of zinc(II), adeninate and biphenyldicarboxylate on the inner wall of a capillary, and theuse of this MOF as a stationary phases in open-tubular capillary electrochromatography. The inner wall of a fused-silica capillary was first modified with 3-aminopropyltriethoxysilane to create surface amino sites, and then the MOF was synthesized by in-situ growth. The modified capillary was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. The results proved the successful growth of the MOF. The resultant open-tubular column showed good separation selectivity towards neutral compounds, acidic and basic compounds including nonsteroidal anti-inflammatory drugs, sulfa drugs and small biomolecules. In addition, the modified column is stable and repeatable. The precisions (expressed as RSDs) of the retention time for intra-day (n= 5) and inter-day (n = 5) separations and between columns (n= 3) are less than 0.5, 1.6 and 4.7%, respectively. Conceivably, this new kind of MOF represents a most useful novel stationary phase in electrochromatographic separations. Graphical abstract Schematic presentation of the open-tubular column modified with bio-MOF-1 by in situ hydrothermal reaction with adeninate, Zn(II) and biphenyldicarboxylate for capillary electrochromatographic separations.

An innovative reversed-phase monolithic column modified with 4-vinylbiphenyl and ionic liquid stationary phases for capillary electrochromatography

A poly(VBP-co-EDMA-co-IL) monolithic column was used for electrochromatographic separation.

Covalent organic framework TpPa-1 as stationary phase for capillary electrochromatographic separation of drugs and food additives.

Because of unique properties like permanent porosity, low density and large surface area, covalent organic frameworks are attractive microporous materials as stationary phase for CEC. Among them, COF-TpPa-1 possesses extraordinary chemical stability and common features of covalent organic frameworks. So, COF-TpPa-1 could be a promising material as stationary phase to enhance separation selectivity and tolerate the acid or alkaline electrochromatographic separation conditions. Here, we report the preparation of COF-TpPa-1 modified capillary column by in situ growth for electrochromatographic separation. The immobilization of COF-TpPa-1 on the inner wall of capillary column was confirmed by Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray diffraction. The fabricated COF-TpPa-1 modified capillary column indicated good resolution for the separation of neutral analytes, nonsteroidal anti-inflammatory drugs and food additives in open-tubular CEC mode. Compared with bare capillary column, the COF-TpPa-1 modified capillary column improved separation selectivity remarkably for tested analytes, including hydrophobic, π-π and hydrogen bond interactions. Besides, the prepared capillary column showed excellent repeatability and stability. The intraday, interday and column-to-column relative standard deviations of migration time for neutral analytes were less than 3.54%. This work shows enamine-linked covalent organic frameworks have great potential as stationary phases in CEC.

Ultrafast preparation of a polyhedral oligomeric silsesquioxane-based ionic liquid hybrid monolith via photoinitiated polymerization, and its application to capillary electrochromatography of aromatic compounds.

An ionic liquid hybrid monolithic capillary column was prepared within 7min via photoinitiated free-radical polymerization of an ionic liquid monomer (1-butyl-3-vinylimidazolium-bis[(trifluoromethyl)sulfonyl]imide); VBIMNTF2) and a methacryl substituted polyhedral oligomeric silsesquioxane (POSS-MA) acting as a cross-linker. The effects of composition of prepolymerization solution and initiation time on the porous structure and electroosmotic flow (EOF) of monolithic column were investigated. The hybrid monolith was characterized by scanning electron microscopy and FTIR. Owing to the introduction of a rigid nanosized POSS silica core and ionic liquids with multiple interaction sites, the monolithic column has a well-defined 3D skeleton morphology, good mechanical stability, and a stable anodic electroosmotic flow. The hybrid monolithic stationary phase was applied to the capillary electrochromatographic separation of various alkylbenzenes, phenols, anilines and polycyclic aromatic hydrocarbons (PAHs). The column efficiency is highest (98,000 plates/m) in case of alkylbenzenes. Mixed-mode retention mechanisms including hydrophobic interactions, π-π stacking, electrostatic interaction and electrophoretic mobility can be observed. This indicates the potential of this material in terms of efficient separation of analytes of different structural type. Graphical Abstract Preparation of a mixed-mode ionic liquid hybrid monolithic column via photoinitiated polymerization of methacryl substituted polyhedral oligomeric silsesquioxane (POSS-MA) and 1-butyl-3-vinylimidazolium-bis[(trifluoromethyl)sulfonyl]imide (VBIMNTF2) ionic liquid for use in capillary electrochromatography.

Preparation of β-cyclodextrin-gold nanoparticles modified open tubular column for capillary electrochromatographic separation of chiral drugs.

In this paper, β-cyclodextrin (β-CD) modified gold nanoparticles (AuNPs) coated open tubular column (OT column) was prepared for capillary electrochromatography. The open tubular column was constructed through self-assembly of gold nanoparticles on 3-mercaptopropyl-trimethoxysilane (MPTMS) prederivatized capillary and subsequent modification of thiols β-cyclodextrin (SH-β-CD). Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and ultraviolet visible spectroscopy were carried out to characterize the prepared open tubular column and synthesized gold nanoparticles. By comparing different coating times of gold nanoparticles and thiols β-cyclodextrin, we got the optimal conditions for preparing the open tubular column. Also, the separation parameters were optimized including buffer pH, buffer concentration and applied voltage. Separation effectiveness of open tubular column was verified by the separation of four pairs of drug enantiomers including bifonazole, fexofenadine, omeprazole and lansoprazole, and satisfactory separation results were achieved for these analytes studied. In addition, the column showed good stability and repeatability. The relative standard deviation values less than 5% were obtained through intra-day, inter-day, and column-to-column investigations.

Recent highlights in electro-driven separations- selected applications of alkylthiol gold nanoparticles in capillary electrophoresis and capillary electro-chromatography.

To date, alkylthiol gold nanoparticles (AuNPs) have been widely used in electro-chromatographic separation techniques as a viable alternative to traditional stationary phases. This is mainly due to their stability, chemical inertness, ease of functionality, increased phase ratio, ability to form self-assembled monolayers. They also yield versatile stationary phases with highly specific targeted functionalities. At the nanoscale region, the chemical and physical properties of a molecule display different attributes to that of the parent molecules or material, hence these features can be harnessed in electro-driven chromatographic separations. Application areas illustrating the use of AuNPs in separation science continue to grow and expand to cover many different kinds of analysis. The last decade has witnessed a successful trend in miniaturisation of chemical separation systems toward the micro and nanoscale ranges. Nanoparticle-based stationary phases fit well with performing chemical separations on microfluidic and capillary platforms. In this review the theory of the use of alkylthiol gold nanoparticles in electro-chromatographic driven separation methods will be discussed. This will be followed by details of recent and selected applications showing alkylthiol gold nanoparticles in capillary electrophoretic and open-tubular electro-chromatographic separations. This review will focus solely on alkylthiol based gold nanoparticles, therefore other kinds of chemical moieties bonded to gold nanoparticles are outside the scope of this review. Finally the future outlook of this exciting technology will be outlined in some detail in the final section.

Preparation of a Sulfoalkylbetaine-Based Zwitterionic Monolith with Enhanced Hydrophilicity for Capillary Electrochromatography Separation Applications

A novel monolithic stationary phase based on in situ copolymerization of zwitterionic monomer N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropyl) ammonium betaine (DMMSA), pentaerythritol triacrylate (PETA), either methacrylatoethyl trimethyl ammonium chloride (META) or sodium 2-methylpropene-1-sulfonate (MPS) was designed as a multifunctional separation column for hydrophilic interaction capillary electrochromatography (HI-CEC). A significantly enhanced hydrophilicity was obtained on the poly(DMMSA-co-PETA-co-META or MPS) monolith, which was contributed by the high percentage of DMMSA in the polymerization mixture. A column efficiency of 200,000 plates/m was obtained and the monolithic column also displayed a satisfactory repeatability in terms of migration time with RSD values less than 1.1% (intra-day, n = 5) and 2.0% (inter-day, n = 3). Most importantly, the column was successfully applied to separation of a pool of neurotransmitters which are not well separated on commercial HILIC packing materials. A baseline separation of the 12 model components was obtained with good selectivity, symmetrical peak shape and high column efficiency with BGE consisting of 20 mM ammonium formate (pH 3.0) in ACN/H2O (80/20, v/v).