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Electroosmotic flow significantly impacts the resolution of separations in capillary electrophoresis and its modification is often necessary. Coating of the inner capillary surface either dynamically or permanently offers a way to alter the electroosmotic flow, potentially reducing the adsorption of analytes, in our case liposomes, to the capillary wall. At first, we measured fluorescently labeled liposomes in an uncoated capillary by capillary electrophoresis with laser-induced fluorescence detection. We used a special procedure of the electrophoretic experiment allowing us to observe the development of peak shape at the early stages of migration. We proved that the liposomes were adsorbed to the capillary wall, which led to a very quick and severe dispersion of their peak during their electromigration. For this reason, we used a commercially coated capillary with polyvinyl alcohol, where at the same separation conditions, we observed the peak of the liposome with a stable shape during the migration. However, this capillary is costly, thus four simple dynamic coating methods were tested for four polymers, namely Pluronic F-127, polyvinyl pyrrolidone K30, polyethylene glycol, and polydiallyldimethylammonium chloride. Among them, we chose a method where we flushed the capillary with a 10% solution of polyvinyl pyrrolidone K30 before the first measurement. In addition, in-house made permanent coating with linear polyacrylamide was investigated, which has led to effective suppression of the electroosmotic flow and stable liposome peak, not dispersed during its migration. Liposome separation using this coating fully confirmed that the studied liposomes are negatively charged and migrate in the anodic direction. [ABSTRACT FROM AUTHOR]

The choice between capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC) is not easy and depends on many factors. An attempt to facilitate this choice is this work, in which both techniques have been confronted on the basis of the RGB model, offering a transparent and pictorial way to compare individual parameters as well as the overall analytical potential of each tool. To ensure the universal nature of the comparison, a simple in composition and chemically diverse model sample was used, accompanied by the data processing method reducing the potential impact of analyte selection. Moreover, permanent coating of the inner surface of the capillary and addition of a surfactant to the separation buffer were considered as the additional factors that may affect the assessment of the CE technique. The presented analysis can be valuable in any discussions about the intrinsic advantages and disadvantages of CE and HPLC, and divagations on how they affect the overall potential and usability of each. We also provide access to the Excel worksheets used for the assessment, which can be easily modified to reevaluate the methods with a different selection of variables, and analyze other possible scenarios. [ABSTRACT FROM AUTHOR]

An electrochromatographic capillary was modified with graphene oxide (GO), and the coating was characterized by scanning electron microscopy, energy dispersive X-ray spectrometry, and Fourier transform infrared spectra. By utilizing maltodextrin (MD) as the chiral selector, the basic chiral drugs nefopam (NEF), amlodipine (AML), citalopram hydrobromide (CIT), econazole (ECO), ketoconazole (KET) and cetirizine hydrochloride (CET) can be enantiomerically separated on this CEC. Compared with an uncoated silica capillary, the resolutions are markedly improved (AML: 0.32 → 1.45; ECO: 0.55 → 1.89; KET: 0.88 → 4.77; CET: 0.81 → 2.46; NEF: 1.46 → 2.83; CIT: 1.77 → 4.38). Molecular modeling was applied to demonstrate the mechanism of enantioseparation, which showed a good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

A poor repeatability of migration times caused by the fluctuations of electroosmotic flow (EOF) is an inherent weakness of capillary electrophoresis. Most researchers endeavor to prevent this problem using relative migration times or various capillary coatings which are expensive and not easy in comparison. Herein, we present an original approach to this problem: we apply a model sample designed to induce significant EOF instability, in order to critically compare ten capillary types with different physicochemical characteristics. Moreover, we accompany capillary modification with the evaluation of various criteria of peak identification: migration time, migration times ratio, and electrophoretic mobility. Our results show a great effectiveness of a dynamic coating in the stabilization of migration times, with the average RSD(%) value reduced from 3.5% (bare silica capillary) down to 0.5%. The good outcomes were also obtained for the surfactant-modified silica and amine capillaries. For the capillaries exhibiting significant instability of EOF, electrophoretic mobility turned out to be a more universal and reliable criterion of peak identification than relative migration time. It can be explained by an intrinsic dependency of migration times ratio on EOF change, which should always be considered during the selection of an internal standard. [ABSTRACT FROM AUTHOR]

A strategic modification of acidity (p K values) by the non-covalent host-guest interactions is one of the most promising concepts in current supramolecular chemistry. This work is aimed at enhancing the effectiveness of capillary electrophoresis (CE) in determination of p K shifts caused by such interactions and their thermal dependencies crucial in a deep thermodynamic description. We show how to (i) minimize the systematic errors related to Joule heating, (ii) minimize the influence of a voltage ramp time, (iii) speed up p K shift identification and estimation, (iv) interpret thermal effects related to two overlapped dynamic equilibria, and (v) determine p K shifts by an alternative spectrophotometric method (CE-DAD). The proposed solutions were implemented to examine the supramolecular p K shifts of several coumarin derivatives, caused by a variety of structurally different cyclodextrins. It was revealed that a specific host substitution pattern determines the magnitude of apparent p K shifts. Accordingly, heptakis(2,6-di- O-methyl)-β-cyclodextrin induces the much stronger shifts than both non-methylated-β-cyclodextrin and heptakis(2,3,6-tri- O-methyl)-β-cyclodextrin applied at the same concentration. We also show that insofar as the complexation of 4-hydroxycoumarin and its derivative (coumatetralyl) are similarly exothermic, the thermal effects accompanying the deprotonation process are remarkably different for both molecules. The p K shift induced by complexation with calixarene was also for the first time determined by a CE method. These observations throw a new light on the background of acidity modification and confirm the applicability of CE as an analytical tool. [ABSTRACT FROM AUTHOR]

Statically, chitosan-coated capillaries were simply dynamically coated with multiwall carbon nanotubes (MWNTs) coaggregated with sodium dodecyl sulfate (SDS). The capillary electrophoresis method was used to separate natural antioxidants in plant and beverage samples. In this way, a great improvement in the electrophoretic resolution was achieved when the running buffer was composed of 50 mM SDS and 10 mM sodium borate with 6.0 μg/mL of SDS-coated MWNTs, at pH 8.0, with an applied voltage of 30 kV. Under the optimal conditions, the limits of detection and quantitation for the target analytes were in the range of 0.14-0.82 μg/mL and of 0.47-2.75 μg/mL, respectively. The mean recovery values of 83.9-106.2 % were obtained for the spiked chrysanthemum samples. This proposed method was successfully applied for determining 12 phenolic compounds in complex chrysanthemum samples. [ABSTRACT FROM AUTHOR]

The choice between bare and coated capillaries is a key decision in the development and use of any methods based on capillary electrophoresis. In this work several permanently and dynamically coated capillaries were successfully implemented in a previously developed micellar electrokinetic chromatography (MEKC) assay of the plant membrane enzyme chlorophyllase. The results obtained demonstrate the rationale behind the use of capillary coating, which is crucial for successful optimization of both the off-line mode and the on-line/electrophoretically mediated microanalysis assay mode. The application of an amine permanently coated capillary (eCAP) is a simple way to significantly increase the repeatability of migration times and peak areas, and to ensure a strong electroosmotic flow that considerably decreases the overall analysis time. A dynamic coating (CEofix) allows one to apply an on-line incubation to control the reaction progress inside the capillary, and to increase the signal-to-noise ratio and peak efficiency. The dynamic coating is possible with use of both the normally applied uncoated silica capillary and the precoated amine capillary, which ensures more repeatable migration times. The strong points of the uncoated silica capillary are its attractive price and wide range of pH that can be applied. The characteristics presented may simplify the choice of capillary modification, especially in the case of hydrophobic analytes, MEKC-based separations, and other enzymatic assays. [ABSTRACT FROM AUTHOR]

A new method for the fabrication of covalently cross-linked capillary coatings of poly(ethylene glycol) (PEG) is described using diazotized PEG (diazo-PEG) as a new photosensitive coating agent. The film of diazo-PEG depends on ionic bonding and was first prepared on the inner surface of capillary by self-assembly, and ionic bonding was converted into covalent bonding after reaction of ultraviolet light with diazo groups through unique photochemical reaction. The covalently bonded coating impedance adsorption of protein on the central surface of capillary and hence the four proteins ribonuclease A, cytochrome c, bovine serum albumin, and lysosome can be baseline separated by using capillary electrophoresis (CE). The covalently cross-linked diazo-PEG capillary column coatings not only improved the CE separation performance for proteins compared to non-covalently cross-linked coatings or bare capillary but also showed a remarkable chemical solidity and repeatability. Because photosensitive diazo-PEG took the place of the highly noxious and silane moisture-sensitive coating reagents in the fabrication of covalent coating, this technique shows the advantage of being environment-friendly and having a high efficiency for CE to make the covalently bonded capillaries. [ABSTRACT FROM AUTHOR]

The design of novel stationary phases is a permanent demanding challenge in chromatographic and electrophoretic separation science to enable analysis with enhanced selectivity, specificity and speed. Therefore, the characterization of chemical and physical properties is next to calculation of chromatographic parameters essential. Conventionally, column performance is checked by a test run which only enables to prove efficiency column by column. Chemical parameters including surface coverage is normally analyzed by burning combustion or frontal analysis, physical parameters including particle size, pore size, pore volume and surface area by SEM, mercury intrusion porosimetry and Brunauer Emmett Teller. All these methods are extremely time consuming, invasive and require, beside special equipment, some specially trained lab staff. In order to enable a fast high-throughput control of chemical and physical parameters we introduced near-infrared spectroscopy (NIRS, 4,000-10,000 cm) as a non-invasive, easy-to-handle technology enabling simultaneous analysis within only a few seconds at higher precision than the conventional applied methods. The method is applicable to porous/non-porous silica gel, carbon-based nano-materials (e.g. fullerenes), polymer beads, monoliths for solid-phase extraction, liquid chromatography, micro-liquid chromatography, material-enhanced laser desorption ionization and coated capillaries for capillary electrophoresis and capillary electrochromatography. Different carriers themselves and their kind of chemical derivatization (reversed-phase, normal-phase, ion-exchanger, immobilized affinity chromatography, affinity, endcapping) can be determined by applying principal component analysis of spectra recorded. Partial least square regression enables the determination of physical parameters particle size, pore size, pore volume, porosity, total porosity and surface area with one single measurement in an established quantitative model. For a detailed investigation NIRS imaging, which benefits from the combination of a NIR spectrometer with a microscope, allows to analyze materials of interest with resolution down to 4 μm. For the optimized design of polymeric phases real-time in situ monitoring to control polymerization progress can be highly helpful. In this article, the advantages of this novel infrared-based method for the fast high-throughput quality control are introduced. [ABSTRACT FROM AUTHOR]

The performance of different capillary coatings and their ability to reduce peptide/wall interactions in capillary zone electrophoresis (CZE) was evaluated through the separations of standard peptides with PM ranging from 720 to 3500 and pl ranging from 3.0 to 11.5. The study was performed in acidic buffer with untreated fused silica capillary, poly(vinylalcohol) (PVA) modified capillary (generated in our laboratory by immobilization with thermal treatment of a PVA solution) and polybrene coated capillary. PVA and polybrene modified capillaries were shown to produce higher reproducibilities for migration times and superior efficiencies in comparison to the uncoated capillary. Peak efficiencies of acidic peptides were 300000 to 650000 (N/m) with polybrene capillary coating while PVA coating produced high efficiencies (N/m>330000) for the most basic peptides. An efficient peptide mapping of the β-lactoglobulin was obtained in less than 20 min using the polybrene coating. Attempts to separate the peptide digest from a deglycosylated form of the rgp 160, a very complex and heterogeneous HIV envelope glycoprotein, were not fully satisfactory but the results demonstrate the potential of capillary surface treatment in producing peptide maps. [ABSTRACT FROM AUTHOR]

A star-shaped molecularly imprinted coating was prepared starting from octavinyl-modified polyhedral oligomeric silsesquioxanes (Ov-POSS). It possesses a relatively open structure and has good site accessibility and a larger capacity even at lower cross-linking. The imprinted coating was prepared from S-amlodipine (S-AML) as the template and analyte, Ov-POSS as the cross-linker, and methacrylic acid as the functional monomer. The preparation and chromatographic parameters were optimized, including ratio of template to functional monomer, apparent cross-linking degree, pH value, ACN content and salt concentration in the mobile phase. The best resolution in enantiomer separation by means of capillary electrochromatography reaches a value of 33. A good recognition ability (α = 2.60) was obtained and the column efficiency for S-AML was 54,000 plates m−1. The use of Ov-POSS as a cross-linker significantly improves the column capacity and thus the detection sensitivity. The results show that Ov-POSS is an effective cross-linker for the preparation of imprinted polymers with good accessibility and large capacity.Schematic presentation of the preparation of star-shaped imprinted polymer using octavinyl-modified polyhedral oligomeric silsesquioxanes (Ov-POSS) and by using methacrylic acid (MAA) as functional monomer. The best enantiometric resolution (33) for amlodipine (AML) can be achieved in capillary chromatography (CEC). [ABSTRACT FROM AUTHOR]