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Background: The objective of this study was to determine the features of fragment length for circulating cell-free DNA (cfDNA) from plasma and serum samples. Methods: Plasma and serum samples from different sources were randomly collected. Circulating cfDNA was extracted and purified by a precipitation-enriched and spin-column-based kit. The concentration of the purified DNA was immediately measured by a highly sensitive dsDNA quantitative assay, and then the fragment length was analyzed by capillary electrophoresis. The abundance of a specific fragment was estimated by the area under curve (AUC) for the fragment peak in the capillary electrophoresis. Results: A total of 199 plasma and 117 serum samples were extracted and analyzed. The average yield of cfDNA from the serum samples (131.67 ng/mL) was significantly higher than that from the plasma samples (32.78 ng/mL, p < 0.001). The average abundance of the 20–400 bp fragments in plasma cfDNA (84.4%) was significantly higher than that of serum cfDNA (51.9%, p < 0.001). Fragment peaks in serum cfDNA always presented in regions around 190 bp, 430 bp, and 630 bp, but plasma cfDNA generally showed a sharp peak in the 165–190 bp region and a much lower peak in the 300

Metal-organic cages (MOCs) are a novel kind of porous materials which have three dimensional structures with perpetual and well-defined holes. They have attracted wide consideration for relatively simple synthesis and potential applications such as separation, sensing, microreactor and catalysis etc. In this study, a homochiral MOC [Zn 3 L 2 ] was prepared as a novel stereoselective stationary phase and added into poly (ionic liquid- co -ethylene dimethacrylate) (Zn 3 L 2 @poly(IL- co -EDMA)) monolith for capillary electrochromatography (CEC). The chiral analytes comprising mandelic acid, benzoin and furoin enantiomer were separated perfectly using the monolithic column Zn 3 L 2 @poly(IL- co -EDMA), and the effects of buffer pH, acetonitrile percentage and buffer concentration on enantiomers separation were confirmed. Moreover, incorporation of MOC [Zn 3 L 2 ] into IL polymer monolith strengthened obviously the stereoselective isolation of some positional isomers (such as nitrophenols, nitrotoluenes, xylenes, and ionones). The relative standard deviations (RSDs) of the retention time for intra-day (n = 5) and inter-day (n = 3) and column-to-column (n = 3) enantioseparations were all below 5.0%. This novel monolithic column combined distinct features of the stereoselective materials with the eminent traits of ionic liquid matrix, it has great application potential in CEC. Image 1 • Homochiral MOC [Zn 3 L 2 ] was first used as novel stationary phases for CEC. • The Zn 3 L 2 @poly(IL- co -EDMA) monolith was successfully prepared by one-step copolymerization. • The monolithic column showed good separation selectivity for isomers and enantiomers. • The Zn 3 L 2 @poly(IL- co -EDMA) monoliths exhibited excellent reproducibility and stability. [ABSTRACT FROM AUTHOR]

This review critically discusses the developments on open-tubular liquid chromatography (OT-LC) and open-tubular capillary electrochromatography (OT-CEC) during 2014–2018. An appropriate Scopus search revealed 5 reviews, 4 theoretical papers on open-tubular format chromatography, 29 OT-LC articles, 68 OT-CEC articles and 4 OT-LC/OT-CEC articles, indicating a sustained interest in these areas. The open-tubular format typically uses a capillary column with inner walls that are coated with an ample layer or coating of solid stationary phase material. The ratio between the capillary internal diameter and coating thickness (CID/CT) is ideally ≤ 100 for appropriate chromatographic retention. We, therefore, approximated the CID/CT ratios and found that 22 OT-LC papers have CID/CT ratios ≤100. The other 7 OT-LC papers have CID/CT ratio >100 but have clearly demonstrated chromatographic retention. These 29 papers utilised reversed phase or ion exchange mechanisms using known or innovative solid stationary phase materials (e.g. metal organic frameworks), stationary pseudophases from ionic surfactants or porous supports. On the other hand, we found that 68 OT-CEC papers, 7 OT-LC papers and 4 OT-LC & OT-CEC papers have CID/CT ratios >100. Notably, 44 papers (42 OT-CEC and 2 OT-LC & OT-CEC) did not report the retention factor and/or effective electrophoretic mobility of analytes. Considering all covered papers, the most popular activity was on the development of new chromatographic materials as coatings. However, we encourage OT-CEC researchers to not only characterise changes in the electroosmotic flow but also verify the interaction of the analytes with the coating. In addition, the articles reported were largely driven by stationary phase or support development and not by practical applications. Image 1 • Developments in OT-LC and OT-CEC during 2014–2018 were critically reviewed. • Appropriate coating thickness inside narrow capillaries were implemented in OT-LC. • Lack of rigour in reporting the chromatographic effect of coatings in OT-CEC. • OT-LC and OT-CEC are still in the exploratory or research phase. • Focus was on development of innovative stationary phase materials and supports. [ABSTRACT FROM AUTHOR]

Surfactant bilayers or admicelles at the solid surface-liquid interface inside 50–200 μm inner diameter (i.d.) open-tube fused-silica capillaries were developed as 'soft' stationary pseudophases for the liquid chromatographic (LC) separations of neutral and charged analytes. Admicelles were formed in-situ from buffered aqueous mobile phases with cetytrimethylammonium bromide at concentrations between the critical surface aggregation concentration and critical micelle concentration, which were determined by electroosmotic flow measurements using capillary electrophoresis. There were no micelles in the mobile phase solution. Also, there was no solid phase that is classically required in LC. Pressure and voltage driven modes or open-tubular admicellar liquid chromatography (OT-AMLC) and electrochromatography, respectively were proposed based on the separation of neutral analytes. The parameters (i.e., pH, concentration of surfactant, salt, and methanol in the mobile phase and capillary i.d.) that affected the surprising chromatographic effect of admicelles at the interface were investigated. The analytical performance of OT-AMLC for small molecules were found acceptable. Applications to environmental water and biological (HepG cell line metabolism media) samples analysis with appropriate sample preparation procedures were also conducted. The use of pseudophases at the solid surface-liquid interface could be a viable solution to problems associated with the use of solid stationary or support materials in nano- and micro-liquid chromatography and electrochromatography. Image 1 • Open-tubular chromatography and electrochromatography without a solid stationary phase or support. • CTAB admicelles at the inner fused silica capillary surface-liquid interface. • Admicelles as stationary pseudophase in chromatography and electrochromatography. • Separation of neutral and charged analytes. • Potential for applications to environmental and biological sample analysis. [ABSTRACT FROM AUTHOR]

• Multi-particles serve as frits for packed columns based on keystone effect. • Multi-particle frits are short, permeable and of easy preparation. • Multi-particle fritting is feasible for CEC columns of various inter diameters. • Good over-run and over-column reproducibilities were obtained. Further development of capillary electrochromatography (CEC) is to some extent restricted by column technology. Packed capillary columns are most commonly used in CEC because of higher sample capacity and higher sensitivity than open tubular columns, and better reproducibility and uniformity than monolithic columns. Fritting is the core component for the fabrication of packed capillary columns. Therefore various fritting technologies attract continuous attention from analytical community. A convenient fritting method was developed in this study. In contrast to the reported single-particle fritting, this method applies a multi-particle fritting technology to hold stationary phase in capillary columns. Several large porous particles smaller than the column internal diameter were tapped in and immobilized in inlet and outlet of the packing material bed due to direct and indirect keystone effect. Except the smallest permeability by the sintered frit and the lowest breaking pressure by the single-particle frit, EOF mobility and peak dispersion of the multi-particle frit were at the same levels with the formers. In addition, all the three frits avoided bubble formation. It demonstrated that the multi-particle frits met the general requirements of permeability, mechanical resistance and efficiency for packing capillary microcolumns as well as the sintered frits and the single-particle frits. Thus, peak efficiency around 4.3 μm plate height (approximately 232,560 plates per meter) was obtained by multi-particle fritted capillary columns with electrokinetic packing, compared to 6.5 μm plate height by single-particle fritted columns with slurry pressure packing. In particular, the multi-particle fritting was simpler, faster, and more reproducible than the sintered fritting, and the multi-particle fritting was suitable to pack capillary columns of various capillary bore sizes owing to rich commercial resources of fritting particles of various diameters. Multi-particle fritted columns offered satisfactory run-to-run and column-to-column reproducibilities for retention factor, plate height and peak area (precisions of 4.1–9.3% for 10 replicated columns, and precisions of 0.9–3.1% for 30 replicated trials). They also had consistent CEC performance (differences of 1.1–3.9% between the first and 31 st day) during a lifetime more than one month. Application examples in packing capillary columns of 75 and 100 μm i.d. and CEC analysis of sixteen polycyclic aromatic hydrocarbons prove the diversity and reliability of the multi-particle fritting in column technology. [ABSTRACT FROM AUTHOR]

Concepts leading to single enantiomers of chiral molecules are of crucial importance for many applications, including pharmacology and biotechnology. Recently, mesoporous metal phases encoded with chiral information have been developed. Fine‐tuning of the enantioaffinity of such structures by imposing an electric potential is proposed, which can influence the electrostatic interactions between the chiral metal and the target enantiomer. This allows the binding affinity between the chiral metal and the target enantiomer to be increased, and thus, the discrimination between two enantiomers to be improved. The concept is illustrated by generating chiral encoded metals in a microfluidic channel by reduction of a platinum salt in the presence of a liquid crystal and l‐tryptophan as a chiral model template. After removal of the template molecules, the modified microchannel retains a pronounced chiral character. The chiral recognition efficiency of the microchannel can be fine‐tuned by applying a suitable potential to the metal phase. This enables the separation of both components of a racemate flowing through the channel. The approach constitutes a promising and complementary strategy in the frame of chiral discrimination technologies. In for a shock: The electric potential of a mesoporous chiral platinum phase can be tuned to allow quantitative separation of the enantiomers in a tryptophan racemate. An applied potential influences the electrostatic interactions, and thereby the enantioaffinity, between the chiral metal and the target enantiomer. [ABSTRACT FROM AUTHOR]

Core-shell particle is a new generation high performance packing material for liquid chromatography. Through comparison with a classical totally porous silica phase of the same particle size, we studied Ascentis Express 5 μm core-shell particle's electrochromatographic behavior, in terms of voltage-current property, electroosmotic flow (EOF) and van Deemter curve. It was found, due to the nonpermeable solid core, the core-shell particle presented a diminished EOF and efficiency than the totally porous paricle. This on the other hand proved that the intra-particle pore flow extensively exists and plays an important role in electrochromatography on totally porous material. The core-shell particle's high retentivity led to an enhanced resolution for weakly retained hydrophilic peptides, which were poorly retained and co-eluted on totally porous particles. Further exploration has shown the core-shell material can achieve efficient electrochromatography of protein digests, excellent performance in terms of resolution, reproducibility and long term stability have been observed. The results indicate that the core-shell structure may suggest a reasonable design of stationary phase for bioelectrochromatography of peptides and proteins. [ABSTRACT FROM AUTHOR]

A carbamoylated clarithromycin‐incorporated zirconia hybrid monolith (CLA‐ZHM) was prepared in a fused silica capillary via an in situ sol–gel process. The CLA‐ZHM capillary column was employed for enantiomer separation of acidic chiral compounds by capillary electrochromatography in eluents consisting of acetonitrile, methanol, and acetic acid and triethylamine as electrolytes. Influences of the composition of eluent and applied voltage on enantiomer separation were investigated. Baseline resolutions were achieved for 10 acidic compounds in an eluent consisting of 70/30 acetonitrile/methanol with 255 mM acetic acid and 17.4 mM triethylamine at an applied voltage of −10 kV and capillary temperature of 25 °C. Relative standard deviation values in resolution parameters for column to column and batch to batch repeatability were less than 2.7% (for n = 3) under the optimal separation settings, indicating that stability of the ZHM columns and reproducibility of the column preparation method are acceptable. [ABSTRACT FROM AUTHOR]

Bacteria, the microorganism with intrinsic chirality, have numerous fascinating chiral phenomena such as various chirality-triggered biological processes and behaviors. Herein, bacteria were firstly explored as novel chiral stationary phases in open-tubular capillary electrochromatography (OT-CEC) for enantioseparation of fluoroquinolone enantiomers and simultaneous separation of six fluoroquinolone antibiotics. The model strain, i.e. non-pathogenic Escherichia coli ( E. coli ) DH5α, was adhered onto the inner surface of positively charged polyethyleneimine (PEI) modified capillaries based on the bacterial adhesion characteristics and strong electrostatic interaction. The morphology and thickness of the bacteria adhesive coatings in the capillary were characterized by field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). Baseline separation of ofloxacin and partial separation of lomefloxacin enantiomers could be achieved by the E. coli coated columns. The preparation parameters including the coating time and concentration of bacteria that affecting the chiral resolution were intensively investigated. The electrophoretic parameters, including pH, buffer concentration and applied voltage, were also optimized. The developed method was validated (linearity, LOD, LOQ, intra-day, inter-day and column-to-column repeatability and recovery) and successfully utilized for the quantitative analysis of ofloxacin enantiomers in the ofloxacin tablets. Moreover, only a slight decrease in the separation efficiency was observed after 90 consecutive runs on the E. coli @capillary. These results demonstrated that bacteria are promising stationary phases for chiral separation in CEC. [ABSTRACT FROM AUTHOR]

The orthogonal pressurized planar electrochromatography (OPPEC) is an example of 2-D separation technique, in which two simultaneous and orthogonal processes of electrophoresis and chromatography are involved in the separation mechanism. In the case of preparative separation of substances characterized by different electrophoretic mobility, such separation system can be constantly fed with the sample solution and the separated components can be constantly collected at its outlet. In the paper, as opposed to the previous studies, we discuss the capabilities of OPPEC technique for preparative separation of substances characterized by the same electrophoretic mobility. According to the proposed solution, the separation system can be periodically fed with the sample solution and separated components can be collected alternately at its outlet. The advantages of this new approach over the column chromatography with regard to the separation of complex mixtures have been signaled. [ABSTRACT FROM AUTHOR]

Carboxylated single-walled carbon nanotubes (c-SWNTs) were incorporated into poly(glycidylmethacrylate-co-ethylene glycol dimethacrylate) [poly(GMA-co-EDMA)] monoliths to develop a novel monolithic stationary phase for capillary electrochromatography. The prepared monoliths were characterized by scanning electron microscopy and nitrogen adsorption. Additionally, pepsin, which is a chiral selector, was bonded to the c-SWNT-incorporated monoliths via epoxide groups as reactive sites and glutaraldehyde as the spacer. The effects of the c-SWNT concentration on chiral separation were investigated, and the results suggested that the c-SWNTs played a significant role in improving the separation efficiency, although pepsin was the dominant element in determining the chiral recognition ability of the monolith. Moreover, the influences of buffer pH, operating voltage and sample volume were also studied with (±)-nefopam as a model drug. Under the optimized conditions, the pepsin-modified poly(GMA-c-SWNTs-EDMA) monolith exhibited excellent enantioseparation performance for ten pairs of basic chiral drugs and extended the scope of chiral separation of drug enantiomers. [ABSTRACT FROM AUTHOR]

Fabricating metal-organic frameworks (MOFs) with the use of nucleating agents in the microenvironment have attracted increasing attention recently. Herein, a simple and rapid synthesis method was developed to in situ fabricate homochiral MOF [Zn(s-nip)2]n in the capillary inner wall by using ZnO nanoparticles as efficient nucleating agents for open tubular capillary electrochromatography (OT-CEC) separation of monoamine neurotransmitters enantiomers of epinephrine, isoprenaline and synephrine, the diastereoisomers of ephedrine and pseudoephedrine, the isomers of nitrophenols and analogues of bisphenols with good resolution. The relative standard deviations (RSDs) for the analytes migration time of intra-day, inter-day and column-to-column were in the range of 0.8-2.1% (n = 10), 0.3-3.2% (n = 3) and 3.2-9.3% (n = 3), respectively. Additionally, the homochiral MOF [Zn(s-nip)2]n coated capillary column could be successively used over 260 runs without observable change in the separation efficiency. [ABSTRACT FROM AUTHOR]

Orthogonal pressurized planar electrochromatography (OPPEC) is the new separation technique, in which two simultaneous and orthogonal processes of electrochromatography/electrophoresis and chromatography proceed under external pressure. It means in the OPPEC separation system a mobile phase solution hydrodynamically flows against adsorbent layer of the chromatographic plate and electric field is orthogonally applied to it. This technique can be applied to analytical and preparative separations. In the paper we report influence of some operating variables on continuous preparative OPPEC separation of test dyes in system with HPTLC RP-18W plates from Merck and methanol–buffer mobile phase. The following operation variables are discussed: external pressure exerted on the adsorbent layer, mobile phase flow velocity, and the ratio of flow velocities of the mobile phase to the sample solution, voltage applied to electrodes, modifier concentration in the mobile phase, concentration and pH of buffer. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants which can reach the environment and food in different ways. Because of their high toxicity, two international regulatory institutions, the US Environmental Protection Agency and the European Food Safety Authority, have classified PAHs as priority pollutants, generating an important demand for the detection and identification of PAHs. Thus, sensitive, fast, and cheap methods for the analysis of PAHs in environmental and food samples are urgently needed. Within this context, electrophoresis, in capillary or microchip format, displays attractive features. This review presents and critically discusses the published literature on the different approaches to capillary and microchip electrophoresis analysis of PAHs. [ABSTRACT FROM AUTHOR]

This review covers various approaches now available to enhance the surface area of stationary phases fabricated in the porous layer open tubular (PLOT) format for use in liquid-phase-based separation techniques and catalytic applications. We focus attention on the preparation of porous polymers (monoliths), since many procedures have already been described related to the production of PLOT columns with distinctive properties and coatings at the column wall. We discuss advantages and limitations of these methodologies with regard to materials used and the demonstrated application. [ABSTRACT FROM AUTHOR]

This manuscript is intended to summarize strategies developed to chemically functionalize the surface of porous polymeric materials using the so-called click reactions with the general aim of developing chromatographic stationary phases with well-defined interfacial characteristics. The preparation pathway starts with the synthesis of polymeric materials with micrometre-sized channel-like pores providing enhanced permeability and fast mass transfer. Such monolithic structure is obtained by solvent-induced phase separation occurring in the course of the free radical polymerization of functional monomers and crosslinkers mixture. The presence of functional groups on the monolith surface allows its further functionalization through click chemistry. Herein, implementation of Huisgen, thiol-ene, thiol-yne and diels--alder click-type reactions is discussed for the grafting of molecular and oligomeric selectors. This work undoubtedly highlights click-surface chemistry as a powerful surface modification strategy for tuning, at the molecular level, the chemical nature of pores surface. [ABSTRACT FROM AUTHOR]

Duplex capillary columns, the standard for electrochromatography using optical detection, consist of a packed and an open section. Normally, optical detection is performed in an on-column manner, i.e. at a point right after the packed section. It was deemed that band broadening may take place when an analyte band travels from the packed bed, through the frit and down to the open section. In this study, without using any sintering steps for fritting or window creation, robust packed capillary columns were prepared using transparent capillaries based on single particle fritting technology. The detection point could be easily shifted by simply sliding the transparent column against the ultraviolet (UV) beam. In this way, the band broadening effect was directly evaluated as a function of the detection point, which was positioned before or after the end frit. The consistent van Deemter curves recorded indicate that there was no efficiency difference between the positions investigated. The result proved that the significant band broadening effect previously observed via on-column detection should be caused by the sintered frit used, while the single particle frit made through a purely physical process did not lead to efficiency degradation. The conservative separation performance recorded at different positions around the column's end also suggests the applicability of on-line tandem detection strategy, e.g. UV followed by mass spectrometry (MS), on the same capillary column, which should be a promising approach to mining multiplex detection information from a single microseparation process. [ABSTRACT FROM AUTHOR]

A novel chiral stationary phase consisting of an amidopropyltrimethylammonium chloride divinylbenzene (APAT-DVB) polymer containing the chiral selector heptakis(2,3-di-O-acetyl-6-O-sulfo)-β-cyclodextrin (HSβCD) has been employed in porous layer open tubular (PLOT) capillary column format with various conditions evaluated to optimize the polymerization and chiral selector immobilization. Scanning electron microscopy demonstrated a near homogenous longitudinal open path in the column with a polymer film of uniform thickness. IR spectroscopy characterized the functional groups of the polymer and energy-dispersive X-ray spectroscopy provided further evidence of the successful polymer modification with HSβCD. Optimum electrochromatographic separation conditions were elaborated with respect to organic solvent content and pH of the background electrolyte. Colum-to-column and long-term reproducibility was excellent. The effectiveness of the new capillary column was demonstrated with the successful separation of d-and l-aspartic acid, d- and l-tyrosine and d-and l-lysine. [ABSTRACT FROM AUTHOR]

Highlights: [•] Simplex column configuration with an essentially fully packed bed was introduced. [•] Single particle fritting technology enabled fabrication of robust simplex columns. [•] Simplex column has uniform electric field distribution and higher efficiency. [•] Simplex column configuration should enable regulation of electroseparation speed. [•] Bidirectional electrochromatography was demonstrated using a simplex column. [Copyright &y& Elsevier]

Highlights: [•] We propose and optimize a new procedure to form silica end frits in capillary columns. [•] The method is based on thermal sintering of particles using axial transfer of heat. [•] The method is robust, reproducible and save the polyimide coatings. [•] The obtained frits are short, permeable, resistant, efficient and do not form bubbles. [ABSTRACT FROM AUTHOR]

Highlights: [•] Overpressured layer chromatography (OPLC). [•] Pressurized planar electrochromatography (PPEC). [•] Two dimensional orthogonal combination of OPLC and PPEC into simultaneous process. [•] Orthogonal pressurized planar electrochromatography (OPPEC). [•] Application of OPPEC to preliminary analytical and micro-preparative separations. [Copyright &y& Elsevier]

Highlights: [•] Monolithic phases are prepared with different hydrophobic and fluorous fraction. [•] Phase selectivity is probed using different fluorous and hydrophobic analytes. [•] The strength of different fluorous interactions is determined with CEC migration data. [•] Hypothetical water percentage describes monolithic fluorous/hydrophobic character. [ABSTRACT FROM AUTHOR]

Metal organic frameworks (MOFs), as a novel separation medium s , have in recent years attracted wide consideration in capillary electrochromatography (CEC). However, the instability of frameworks limited the application of the MOF-based chiral separation capillary. Herein, Iron-based γ-cyclodextrin metal-organic framework (Fe-CD-MOF) with mesoporous was developed as the chiral stationary phase in open tubular capillary electrochromatography column (OT-CEC) for the stereoisomer separation of fourteen chiral drugs and one chiral alcohol. The capillary column with MOF coating exhibited the best performance (resolution value: 17.07) for anisodamine in any MOF-based capillary column that has never been reported. Moreover, the effect of pH, buffer concentration, and methanol content has been investigated. The novel coated capillary was also applied for the quantitative analysis of a real sample. The Fe-CD-MOF coated capillary showed outstanding repeatability and stability, with the satisfactory relative standard deviations (RSDs) for intra-day, inter-day, and column-to-column. Finally, the enantioseparation mechanism of the Fe-CD-MOF coated capillary was evaluated by adsorption kinetic experiments. In summary, this work indicated the novel and renewable Fe-CD-MOF was a potential chiral stationary phase in CEC chiral separation. • Fe-based γ-CD-MOF was first utilized as the chiral stationary phase in CEC. • A novel homochiral Fe-CD-MOF coated column was developed. • The coated capillary exhibited outstanding stereoisomer separation ability. • The enantioselectivity of Fe-CD-MOF was proved by adsorption kinetic experiments. [ABSTRACT FROM AUTHOR]

A method of simultaneous separation of water- and fat-soluble vitamins using pressure-assisted CEC with a methacrylate-based capillary monolithic column was developed. In the proposed method, water-soluble vitamins were mainly separated electrophoretically, while fat soluble-ones were separated chromatographically by the interaction with a methacrylate-based monolith. A mixture of six water-soluble and four fat-soluble vitamins was separated simultaneously within 20 min with an isocratic elution using 1 M formic acid (pH 1.9)/acetonitrile (30:70, v/v) containing 10 mM ammonium formate as a mobile phase. When the method was applied to a commercial multivitamin tablet and a spiked one, the vitamins were successfully analyzed, and no influence of the matrix contained in the tablet was observed. [ABSTRACT FROM AUTHOR]

Abstract: Development of capillary electrochromatography (CEC) largely depends on column technology. The past ten years or so have seen a great number of CEC works performed on monolithic columns, due to simplicity and robustness in column fabrication. Monolithic columns eliminate the issue of column fritting, which conventionally made particle-packed capillary columns fragile and introduced nonuniformity to the chromatographic bed. The particulate packing material, however, is still a popular type of stationary phase widely used in CEC, as the rich library of HPLC packing material provides a wide range of choices for chromatographic separations performed in electrodriven mode. In this study, we investigated a purely physical fritting method, single particle fritting technology, to immobilize particulate chromatographic material inside capillary tube in a sinter-free manner to produce robust capillary columns. Single particle fritted columns present significantly improved column-to-column reproducibility (n =10) in peak efficiency, retention factor, peak area and asymmetry (%RSD=5.4, 7.7, 6.2 and 6.1, respectively, at 26kV), enabling their practical application in high throughput parallel analysis using multiple columns. [Copyright &y& Elsevier]

Abstract: This paper details a method for the separation and identification of fourteen organic compounds commonly found as constituents in commercial smokeless powders using a hexyl acrylate-based porous monolith. Capillary electrochromatography (CEC) coupled to UV and time of flight-mass spectrometry (TOF-MS) methods were both explored. The CEC–UV method provides an effective and efficient method for the detection of all components in the additive package of the powder. The TOF-MS procedure provides better sensitivity and selectivity allowing an additional confirmation of the presence of the subset of those compounds, which are detectable via positive and/or negative ion electrospray ionization mass spectrometry. Both methods were used for the analysis of smokeless powder components in a mixed standard as well as in the determination of the composition of the additive package of individual powders. [Copyright &y& Elsevier]

A porous crosslinked organic polymer based on N-acryloxysuccinimide (NAS) and ethylene dimethacrylate (EDMA) was prepared inside 75 µm i.d. fused silica capillary as functionalizable monolithic stationary phase for electrochromatographic applications. Succinimide groups on the monolith surface provide reactive sites able to react readily through standard electrophile-nucleophile chemistry. Propargylamine was used to prepare alkyne functionalized poly(NAS-co-EDMA). Onto this thiol-reactive polymer surface was grafted adamantane units via a photochemically-driven addition reaction. Chemical characterization was performed in situ after each synthetic step by means of Raman spectroscopy and grafting kinetics was investigated to ensure quantitative grafting of 1-adamantanethiol. The as-designed monolithic stationary phase exhibited typical reversed-phase separation mechanism as evidenced by the linear increase of the logarithm of retention factor of neutral aromatic solutes with the increase of the aqueous buffer content in the mobile phase. [ABSTRACT FROM AUTHOR]

Abstract: This work reports the preparation of monolithic zirconia chiral columns for separation of enantiomeric compounds by capillary electrochromatography (CEC). Using sol–gel technology, a porous monolith having interconnected globular-like structure with through-pores is synthesized in the capillary column as a first step in the synthesis of monolithic zirconia chiral capillary columns. In the second step, the surface of the monolith is modified by coating with cellulose tris(3,5-dimethylphenylcarbamate) (CDMPC) as the chiral stationary phase to obtain a chiral column (CDMPCZM). The process of the preparation of the zirconia monolithic capillary column was investigated by varying the concentrations of the components of the sol solution including polyethylene glycol, water and acetic acid. CDMPCZM is mechanically stable and no bubble formation was detected with the applied current of up to 30μA. The enantioseparation behavior of the CDMPCZM columns was investigated by separating a set of 10 representative chiral compounds by varying the applied voltage and pH and organic composition of the aqueous organic mobile phases. [Copyright &y& Elsevier]

Abstract: A chloropropyl-functionalized silica (CP-silica) hybrid monolithic column was synthesized within the confines of a capillary via the sol–gel process using tetramethoxysilane (TMOS) and (3-chloropropyl)-trimethoxysilane (CPTMS) as the precursors. The resulting CP-silica hybrid monolith inside the capillary showed homogeneous macroporous morphology and was well attached to the inner wall of the capillary. The obtained CP-silica hybrid monolithic capillary column demonstrated the inherent hydrophobic property and could be applied as a reversed-phase stationary phase in CEC directly. Due to the great chemical reactivity of the incorporated chloro groups on the hybrid silica monolithic matrix, the chloropropyl moieties on the surface of the hybrid silica monolith matrix could be conveniently further modified by a tertiary amine of N,N-dimethyl-N-dodecylamine (DMDA) via the nucleophilic substitution reaction at 70°C to introduce a dodecyl groups (C12) onto the CP-silica hybrid monolithic matrix. The resulting C12-silica hybrid monolithic column not only demonstrated the significantly enhanced hydrophobic property in the separation of alkylbenzenes in reversed-phase capillary electrochromatography (RP-CEC), but also the strong electroosmotic flow (EOF) in a wide pH range. Five alkylbenzenes could be baseline separated in 3min with column efficiency ranging from 189700 to 221000N/m with a 70% ACN running buffer in CEC. [Copyright &y& Elsevier]

A refractive index sensor has been fabricated in silicon oxynitride by standard UV lithography and dry etching processes. The refractive index sensor consists of a 1D photonic crystal (PhC) embedded in a microfluidic channel addressed by fiber-terminated planar waveguides. Experimental demonstrations performed with several ethanol solutions ranging from a purity of 96.00% (n = 1.36356) to 95.04% (n = 1.36377) yielded a sensitivity ( / n) of 836 nm/RIU and a limit of detection (LOD) of 6 × 10-5 RIU, which is, however, still one order of magnitude higher than the theoretical lower limit of the limit of detection 1.3 × 10-6 RIU. [ABSTRACT FROM AUTHOR]

Abstract: Fabrication of porous frits to retain stationary phases is a critical issue in column preparation for capillary electrochromatography (CEC). In this work, porous frits were prepared by applying an external magnetic field to magnetically responsive particles placed inside a fused-silica capillary. Three batches of uniform magnetite spheres with particle diameters of 0.3, 0.4, and 0.6μm and saturation magnetization values of 73.03, 74.41, and 77.83emu/g, respectively, were used as frit particles and octadecyl- and phenyl-bonded silica gels were packed successfully into frit-containing capillaries. The performance of the resulting magnetically immobilized frits and packed columns was evaluated. The electroosmotic mobilities in capillaries containing outlet frit only were found to be reduced by 2–4% whereas the plate heights of an unretained marker increased by 30–50% as compared to those in open capillaries. These variations are believed to be associated with the inhomogeneities of the packed structure of the frits. The magnetically immobilized frits showed adequate mechanical strength to withstand the flow drag force, allowing separation in capillaries packed with 5-μm stationary phases up to 10–15cm, thus rendering column efficiency and reproducibility comparable with those obtained with sintered frits. Taken together, retaining frits made of uniform magnetite particles serves as a viable alternative to sintered frits for column preparation, which offers several distinct advantages such as ease of preparation, improved durability as compared to sintered frits where the removal of the polyimide coating makes the packed column susceptible to breakage, and use of large-bore capillaries for semipreparative separations. [Copyright &y& Elsevier]

Abstract: Four anion-exchangers of different ion-exchange capacities (21–129μmol/mL) were prepared by coupling diethylaminoethyl to Sepharose 6FF. The adsorbents were used to study the dynamic protein adsorption in ion-exchange electrochromatography with an oscillatory transverse electric field perpendicular to the mobile-phase flow (IEEC). The static adsorption capacity of bovine serum albumin (BSA) increased from 67 to 186mg/mL in the ionic capacity range, but the effective pore diffusion coefficient of the protein decreased from 10.9×10−12 to 1.85×10−12 m2/s with increasing the ionic capacity due to the hindrance effect of the bound protein molecules at the pore entrance. So, the dynamic binding capacity (DBC) of protein in ion-exchange chromatography decreased with increasing the ionic capacity. By applying an electric field of 30mA, the DBC in IEEC packed with ion-exchangers of high ionic capacities (53 and 129μmol/mL) increased significantly (over 30% and 100%, respectively). This was because the high surface charge density led to high electroosmotic flow that enhanced intraparticle mass transfer in IEEC. In comparison, the DBC in IEEC packed with ion-exchangers of low ionic capacities (21 and 35μmol/mL) increased only slightly (ca. 10%) under the same condition. The results indicated the minor effect of electrophoretic mobility on the intraparticle mass transfer. Hence, it is beneficial to use ion-exchangers of high ionic capacity for high-capacity purification of proteins by IEEC. [Copyright &y& Elsevier]

• Lateral electrochromatography (LEC) allows for continuous enantio-separation. • Derived algebraic expressions determine the slopes of concentration trajectories. • Algebraic expressions may assist to optimize LEC for continuous separation. • Separation efficiency depends on the binding selectivity of the stationary phase. • Results of the simulations offer basic designing rules for LEC systems. The separation of enantiomers in a continuous manner represents a nontrivial task. Identical physical properties of an enantiomeric pair render the standard separation methods unusable, and its separation traditionally relies on the use of a chiral environment. Here, we theoretically analyze lateral electrochromatography as a potential method for continuous steady-state enantiomer separation. The developed mathematical model of a lateral electrochromatography device (LEC) treats the stationary (selective) phase as a pseudo-homogeneous environment. The intensity of the solute transport in that phase is given by an effective diffusion coefficient which depends on the degree of solute-stationary phase interactions. Under the assumptions of phase equilibrium and neglected diffusion/dispersion transport, we derived simplified algebraic expressions determining the slopes (deflections) of solute concentration trajectories allowing the solute separation. These expressions may assist in optimizing the LEC geometry and setting the control parameters such as the applied voltage or pressure difference. Numerical simulations on spatially two- and three-dimensional domains are in good agreement with both simplified algebraic predictions and available experimental observations. We show that LEC can separate enantiomers continuously in a steady-state regime under optimized operating conditions. However, the separation efficiency strongly depends on the enantioselectivity of the stationary phase. The results of the simulations also offer basic designing rules for a LEC that is compatible with continuous synthesis and separation of pharmaceuticals and other special chemicals. [ABSTRACT FROM AUTHOR]

Joule heating caused by electric currents is a major problem in scale-up electrochromatography. Here, to predict the temperature effects of lateral electric field electrochromatography and the process conditions required, a mathematical heat transfer model was established, which took into account the physical characteristics, including the electrical conductivity, of the porous medium and the ceramic plate in the gel chamber. The temperatures calculated using this model were within 4 °C of the experimentally measured results. For the lateral enlargement simulation of short columns (4 cm), it was found that when the width was enlarged to > 3 cm, the outlet temperature on the center line did not increase with increasing width. The electric field strength of 1700 V/m was maintained by increasing current strength according to the column size; further, when the gel chamber was enlarged to 0.075 × 0.075 × 0.1 m3, its internal temperature can be controlled within 16 °C under certain operating conditions, and an electric field strength of 1700 V/m can be obtained in the gel chamber. • Electrochromatography in a transverse electric field was mathematically modelled. • Use of a transverse electric field leads to less Joule heating than an axial field. • Scale-up electrochromatography was successfully performed using the model. [ABSTRACT FROM AUTHOR]

A porous monolithic sol-gel column with the solution of methacryloxypropyltrimethoxysilane in toluene with an acid catalyst was quickly prepared using microwave irradiation. Three typical silica based capillary monolithic columns prepared were used to evaluate the separation of some typical model compounds in the modes of CEC, pressure assisted CEC, and low pressure driven separation. Baseline separation of the analytes including thiourea, benzene, toluene, ethyl benzene, biphenyl, and naphthalene could be obtained by the polymer with a length of 10 cm. A scanning electron micrograph of a cross section of the capillary column showed that the gel took the form of a spherical particle aggregate and adhered to the column inner wall. [ABSTRACT FROM AUTHOR]

Abstract: Photopolymerized sol–gel monolithic columns for use in capillary electrochromatography were prepared in 125μm i.d. polyacrylate-coated fused-silica capillaries. The polyacrylate-coating, unlike the polyimide one, is transparent to the radiation used (≈370nm), and thus, no coating removal is necessary. This is a very important particularity since intrinsic capillary column characteristics, such as flexibility and mechanical resistance, are unchanged. A mixture containing metacryloxypropyltrimethoxysilane (MPTMS) as the polymeric precursor, hydrochloric acid as the catalyst, toluene as the porogen and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (Irgacure 819) as the photoinitiator was irradiated at 370nm for 20min inside the capillaries to prepare the columns through sol–gel approach. The versatility and viability of the use of polyacrilate as a new capillary external coating were shown through preparation of two columns under different conditions, which were tested in electrochromatography for separation of standard mixture containing thiourea (marker compound), propylbenzene, phenanthrene and pyrene. [Copyright &y& Elsevier]

Abstract: The use of a phenylalanine (Phe) functionalized tentacle-type polymer coated capillary column for protein separation by open tubular capillary electrochromatography (OTCEC) was demonstrated in this work. The tentacle-type stationary phase was prepared from silanized fused-silica capillaries of 50μm I.D. by glycidyl methacrylate graft polymerization and subsequent Phe functionalization. Due to the amphoteric functional groups of the Phe bonded on the tentacle-type polymer stationary phase, protein separation in the prepared column can be performed under both cathodic and anodic electroosmotic flow (EOF) by varying the pH values of the mobile phase. Model proteins including ribonuclease A (RNase A), myoglobin, transferrin, insulin were baseline separated under cathodic EOF with a mobile phase of pH 8.8. Comparison between the separation result of the four proteins under conditions of OTCEC and capillary zone electrophoresis indicates that the migration behavior of the four proteins in the prepared column was the result of the interplay of chromatographic retention and electrophoretic migration. Besides, three basic proteins including RNase A, cytochrome c (Cyt-c) and lysozyme (Lys) were fully resolved under anodic EOF with an acidic running buffer (pH 2.5). The elution order was the same as the isoelectric point values of the proteins (RNase A

Abstract: A novel preparative electrochromatographic column with seven compartments was developed. The design gave promise to provide transverse, longitudinal or two-dimensional (2D) electric field on the column. The central gel compartment of 2mL was packed with dye–ligand affinity adsorbent. Bovine serum albumin (BSA) was used as a model protein to investigate the dynamic adsorption behavior in the electrochromatography. The effects of various operating variables indicated that the electroosmotic flow on the charged adsorbent surface could promote the intraparticle mass transport of the protein, leading to the increase of its dynamic binding capacity (DBC). Moreover, it was confirmed that the 2D electric field promoted the mass transport more efficiently than a 1D electric filed. Hence, the DBC of BSA was 4.5 times increased with the 2D electric filed as compared to the 2.4 times increase in a 1D electric field. The results have proven that the 2D electrochromatography is promising for high capacity protein adsorption. [Copyright &y& Elsevier]

A novel approach is introduced and evaluated for the preparation of silica-based monoliths by a sol–gel technique where in situ polymerization was carried out by γ-ray irradiation within the capillary. The γ-radiation-initiated synthesis generated radicals directly on the monomer, thereby avoiding use of any initiator. The chromatographic behavior of the capillary monolithic columns was studied in the modes of CEC, p-CEC and low pressure-driven separation, all of which exhibited reversed-phase character. Various operational parameters, such as column temperature, separation voltage, acetonitrile content and buffer pH, were varied to assess their influence on column performance in the separation of a series of neutral compounds including thiourea, benzene, toluene, ethyl benzene, biphenyl and naphthalene. A scanning electron micrograph of a cross-section of the capillary column showed that the gel took the form of a spherical particle aggregate and adhered to the column inner wall. It provided a viable alternative to either thermally initiated or photo polymerization for the preparation of monolithic columns. [ABSTRACT FROM AUTHOR]

Abstract: This review briefly summarizes the present state of the preparation and use of capillary monolithic columns for liquid chromatography (LC) and electrochromatography (EC). Most important approaches to the preparation of monolithic stationary phases based on organic polymers are outlined and the properties of the monoliths obtained are compared with those of classical particulate phases. A few selected applications of monolithic columns are shown to demonstrate the most important advantages of monolithic capillary columns. It is concluded that both the monolithic and particulate capillary columns are important and that judicious choice of the type suitable for a particular application requires careful consideration of the purpose of the separation and the properties of the solutes to be separated. Monolithic columns are substantially younger than packed ones and thus will require further theoretical and experimental study to further improve their preparation and to enable reliable prediction of their properties and applicability; nevertheless, they are very promising for the future. [Copyright &y& Elsevier]

Abstract: Acrylate-based monolithic capillary columns were prepared from fused-silica capillaries using UV photopolymerization. The effect of the pretreatment of the capillary wall surface before polymerization was investigated and several procedures were compared. The columns were characterization by van Deemter curves and SEM imaging. The results indicated that a pre-silanization of the capillary wall in order to introduce methacrylate groups at the wall surface gave similar efficiencies but more homogeneous structures than when the silanization agent was introduced in the polymerization mixture. The conditioning of the capillary before silanization, especially the conditions of basic rinsing was also an important factor. The effect of the dose of UV light that was applied for the polymerization had also been investigated. The results demonstrated that the irradiation energy is a critical parameter. The minimum energy threshold required to obtain a suitable monolith was 3J/cm2 and the maximum was around 12J/cm2. A higher energy destroys the monolith. Within the convenient range of energy, the columns had the same efficiency and a good structure as seen by SEM imaging. Using the optimized procedure for the pretreatment and an adequate energy, the column-to-column repeatability was found good (n =12). The repeatability was obtained for the plate height at two velocity values, the retention factor and the electroosmotic mobility with RSD values below 10. [Copyright &y& Elsevier]

Abstract: The development of the systematic evolution of ligands by exponential enrichment (SELEX) process has allowed the isolation of oligonucleotide sequences (referred as aptamers) with the capacity to recognize various classes of target molecules with high affinity and specificity. At the present time, various analytical aptamer-based formats have been developed as suitable tools for the detection and quantification of numerous targets, possessing many potential advantages over the most popular antibody technology. In this review, the aptamer applicability to the separation, purification and quantification of various analytes by liquid chromatography, capillary electrophoresis and electrochromatography is addressed. [Copyright &y& Elsevier]

This review gives the basic principle of affinity capillary electrophoresis (ACE) and examines its utilization in bioscience on microchips. ACE on chip is used as a separation tool as well as for study of molecular interactions. MEKC and chiral separations on microfluidic systems are described. Applications for measuring bioaffinity are focused on enzyme assay and immunoassay that demonstrate a further development of classical ACE in capillaries. [ABSTRACT FROM AUTHOR]

Abstract: Monolithic supports are a new generation of stationary phases which are typically prepared using a simple molding process carried out within the confines of the capillary. They provide high rates of mass transfer at lower pressure drops, enable much faster separations and the nature of the pores allows easy permeability for large molecules. This review summarizes the current achievements and application of organic polymer-based monolithic columns, silica-based monolithic columns and their application in bioaffinity processing, modern biotechnology, determination of microorganisms and chiral separations. Special attention is paid to microfabricated devices with monolithic supports because their fabrication of particles directly in the channel eliminates the need for a frit and also creates a unique homogeneity of packing. [Copyright &y& Elsevier]

Abstract: We have investigated the basic dependence of electroosmotic flow (EOF) velocity and hydrodynamic dispersion in capillary electrochromatography (CEC) on the variation of applied field and mobile phase ionic strengths employing silica-based particulate and monolithic fixed beds. These porous media have a hierarchical structure characterized by discrete intraparticle (intraskeleton) mesoporous and interparticle (interskeleton) macroporous spatial domains. While the macroporous domains contain quasi-electroneutral electrolyte solution, the ion-permselectivity (charge-selectivity) of the mesoporous domains determines the co-ion exclusion and counter-ion enrichment at electrochemical equilibrium (without superimposed electrical field) which depends on mesopore-scale electrical double layer (EDL) overlap and surface charge density. This adjustable, locally charge-selective transport realized under most general conditions forms the basis for concentration polarization (CP) induced by electrical fields superimposed in CEC. CP characterizes the formation of convective diffusion boundary layers with reduced (depleted CP zone) and increased (enriched CP zone) electrolyte concentration, respectively, at the anodic and cathodic interfaces in fixed beds containing the cation-selective, silica-based particles (or monolith skeleton). CP originates in the electrical field-induced coupled mass and charge transport normal to the charge-selective interfaces and has consequences for the EOF dynamics, hydrodynamic dispersion, and analyte retention in CEC. A secondary EDL with mobile counter-ionic space charge can be induced in the depleted CP zone leading to induced-charge EOF in the macroporous domains. It is characterized by a nonlinear dependence of the average EOF velocities on applied field strength and strong local velocity components tangential to the surface which enhance lateral pore-scale dispersion, thereby decreasing (axial) zone spreading. Differences in the pore space morphology of random-close sphere packings and monoliths criticially affect the intensity of CP and induced-charge EOF in these materials. CP is identified as a key phenomenon in CEC which also influences effective migration and the retention of charged analytes because the local intensity of CP inherently depends on applied field and mobile phase ionic strengths. [Copyright &y& Elsevier]

Abstract: The application of voltage in micro-high performance liquid chromatography (micro-HPLC) creates a system where separation is governed by a hybrid differential migration process, which entails the features of both HPLC and capillary zone electrophoresis (CZE), i.e., chromatographic retention and electrophoretic migration. In this paper, we use our previously published approach to decouple these two mechanisms via analysis of the input data for estimation of electrokinetic parameters, such as conductivity, equivalent lengths, mobilities and velocities. Separation of weakly retained, charged analytes was performed via voltage-assisted micro-HPLC. Contrary to conclusions from data analysis using the conventional definitions of the retention factor, it is shown that our approach allows us to isolate the “chromatographic retention” component and thus, investigate the “modification” of the retention process upon application of voltage in micro-HPLC. It is shown that the traditional approaches of calculating retention factor would erroneously lead to conclusion that the retention behavior of these analytes changes upon application of voltage. However, the approach suggested here demonstrates that under the conditions investigated, most of the charged analytes do not show any significant retention on the columns and that all the changes in their retention times can be attributed to their electrophoretic migration. [Copyright &y& Elsevier]

Abstract: The separation mechanism in capillary electrochromatography (CEC) is a hybrid differential migration process, which entails the features of both high-performance liquid chromatography (HPLC) and capillary zone electrophoresis (CZE), i.e., chromatographic retention and electrophoretic migration. The focus of this paper is on the use of electrokinetic data, such as current, electroosmotic flow (EOF) and column efficiency measurements, that are readily available, for an improved understanding of CEC separations. A framework is presented here for the use of this data for evaluation of a variety of performance parameters including, conductivity ratio, interstitial EOF mobility, porosity, and zeta potential. This framework is applied for characterization of two monolithic columns with different chemistry that were manufactured in-house. The above-mentioned performance parameters were calculated for the two columns and it is found that the poly(VBC–EGDMA–SWNT) monolithic column with the GPTMS–PEI coating offers a significantly improved flow distribution in comparison to the poly(VBC–EGDMA) monolithic column. This observation is confirmed by performing separation of peptides on the two columns and height equivalent of a theoretical plate (HETP) measurements on the resulting peaks. It is shown that following our approach leads to an improved understanding of the separations achieved with the columns and to better column design. [Copyright &y& Elsevier]

Abstract: Different techniques and methods of electrochromatography on “lab on a chip” devices are reviewed. Described approaches include open-channel microchip electrochromatography relying on C8, C18 and novel gold nanoparticle (GNP) coating of microchannel wall; packed-channel microchip electrochromatography with new ways of automated loading and unloading of conventional octadecylsilica beads; monolith-based microchip electrochromatography with tailored casting of stationary phase at the specific places of microfluidic network and novel photolitographically fabricated collocated monolithic structures. Specific issues related to the microchip electrochromatography, i.e. importance of high aspect ratio of the microchannels in the open-channel electrochromatography or approaches eliminating the wall effect in the monolith-based electrochromatography, are discussed. Various applications for environmental, pharmacological, genomic and proteomic analysis are described. The operation parameters of reviewed microsystems are summarized in easy-to-read tables. [Copyright &y& Elsevier]

Abstract: A capacitively coupled contactless conductivity detection (CCD) system has been applied for the detection of neutral synthetic polymers in capillary size-exclusion electrokinetic chromatography (SEEC). Polystyrene standards, that were used as a model compounds, were separated on a capillary column packed with porous 10μm silica particles with an electrokinetically driven mobile phase, and detected by CCD and UV detection simultaneously. Mass-calibration curves for polystyrene were constructed. Satisfactory results were obtained for the linearity, the run-to-run repeatability (&#60;0.2% for the relative retention and &#60;4% for the peak area) and the robustness of the detector. One of the major issues in this preliminary study was to investigate the origin of the peaks observed for the polystyrene standards. The effect of the molar mass of the polystyrenes on the sensitivity was small. Therefore, the signals obtained could not be explained as the result of an increased viscosity and a decreased solution conductivity of the solute zone. An alternative hypothesis is suggested, and recommendations for further research are given. [Copyright &y& Elsevier]