On-line identification of trans- and cis-resveratrol by nonaqueous capillary electrophoresis/fluorescence spectroscopy at 77 K

This work presents a novel method for the accurate determining trans- and cis-resveratrol (3,5,4'-trihydroxystilbene) by nonaqueous capillary electrophoresis/fluorescence spectroscopy at 77 K. The proposed method permits not only the separation of resveratrol isomers, but also ensures that on-line spectra are readily distinguishable and unambiguously assigned. The experimental results also indicate that the effect of nonaqueous capillary electrophoresis buffer and low-temperature technique increase the detection limit by more than 150-fold.     

Silver (I)-Mediated Separations by Nonaqueous Capillary Electrophoresis: Nonaqueous Argentation Electrophoresis

This study represents the first application of Ag(I) charge transfer complexation in nonaqueous capillary electrophoresis. This method applies the principles of argentation chromatography to nonaqueous electrophoretic separations and is termed “nonaqueous argentation electrophoresis”. Since the separations are performed in 100% nonaqueous media, the advantages of nonaqueous solvents, such as enhanced solubility and flexibility in selectivity enhancement, compared to an aqueous or mixed hydroorganic solvent, are realized. A variety of compounds were separated. Qualitatively, the separation of eleven sulfonamides in 100% acetonitrile is shown to improve greatly upon the addition of Ag(I). These results also show that nonaqueous argentation electrophoresis provides fast, well-resolved separations of compounds, such as N-containing heterocyclics, that can selectively complex with Ag(I). Migration data and separation selectivities of these compounds by nonaqueous argentation electrophoresis were compared to previous aqueous argentation electrophoresis results. Selectivities were found to be significantly different for the two separation media. Ag(I) complexation provides an effective means of manipulating selectivity in nonaqueous capillary electrophoresis.     

Modified liquid junction interface for nonaqueous capillary electrophoresis-mass spectrometry

Electrospray ionization (ESI) is the most widely used ionization method in on-line coupling of capillary electrophoresis-mass spectrometry (CE-MS). The conventional coaxial sheath flow electrospray interface is currently being replaced by the more sensitive nanoelectrospray technique. The usual limitation of nanoelectrospray CE-MS interface has been its short lifetime caused by deterioration of the metal coating on the CE capillary terminus. This article describes an easy way to construct a more durable and sensitive nanospray interface for nonaqueous CE-MS. In this approach a very thin glass spray capillary (ca. 30 microm outer diameter) is partly inserted inside the CE capillary, the junction being surrounded by the electrolyte medium, which is in contact with the platinum electrode. The interface was tested with five pharmaceuticals: methadone, pentazocine, levorphanol, dihydrocodeine, and morphine. Detection limits ranged from 12 to 540 fmol. Separation efficiency and reproducibility were also studied. The CE current was found to be stable and the migration times were highly reproducible. All the CE separations were carried out in a nonaqueous background electrolyte solution.     

Nonaqueous capillary electrophoresis using a titania-coated capillary

In this work, an ordered mesoporous titania film was introduced to coat a capillary by means of the sol-gel technique. Its electroosmotic flow (EOF) property was investigated in a variety of nonaqueous media (methanol, formamide and N,N'-dimethylformamide and mixtures of methanol and acetonitrile). The titania-coated capillary exhibited a distinctive EOF behavior, the direction and magnitude of which were strongly dependent on various parameters such as the solvent composition, apparent pH (pH*) and the electrolytes. The nonaqueous capillary electrophoresis separation of several alkaloids was investigated in the positively charged titania-coated capillary. Comparison of separation between coated and uncoated capillaries under optimal nonaqueous conditions was also carried out.     

On-line stacking techniques for the nonaqueous capillary electrophoretic determination of acrylamide in processed food

In the present study, field amplified sample stacking (FASS) techniques in the nonaqueous capillary electrophoresis method (NACE) were introduced for the on-line concentration of the acrylamide to improve acrylamide detection at 210 nm by diode-array detection. Acetonitrile (ACN) as a nonaqueous solvent permits acrylamide to be protonated through the change of its acid-base chemistry, allowing capillary electrophoretic separation of this compound. Choosing 30 mmol L(-1) HClO(4), 20 mmol L(-1) NaClO(4), 218 mmol L(-1) CH(3)COOH in ACN as the separation electrolyte and employing sample stacking methods, the LOD value of acrylamide was decreased to 2.6 ng mL(-1) with electrokinetic injection and 4.4 ng mL(-1) with hydrodynamic injection. Optimized stacking conditions were applied to the determination of acrylamide in several foodstuffs. The method is simple, rapid, inexpensive, and widely applicable for the determination of acrylamide in food samples.     

非水溶液毛细管电泳手性分离

对非水溶液毛细管电泳中手性分离的研究现状和发展趋势进行了简要的评述。主要是以手性分离中所用的手性试剂为线索，对它们在非水溶液中的应用情况及其对分离度、柱效和分离选择性的影响进行综述并与水溶液中的情况作了比较。对于在水溶液中已经得到应用而在非水溶液中未被使用的部分试剂也进行了简要地解释。     

Nonaqueous capillary electrophoresis in coated capillaries: an interesting alternative for proteomic applications

This work brings together some contributions for the use of nonaqueous media for proteomic analysis, for both capillary electrophoresis (CE) separation and the preparation of tryptic digests. First, a ternary nonaqueous buffer consisting of 60/30/10 v/v methanol/acetonitrile/acetic acid with 12.5 mmol/L ammonium acetate was optimized for CE separation of the tryptic digest of lysozyme. Lysozyme was chosen as a model system for the protein digestion, which has also been prepared in an organic-rich medium with methanol/50 mmol/L NH(4)HCO(3), pH 8.0 (60/40 v/v). The separation results were compared to in silico (PeptideCutter program) digestion conditions, and high-efficiency peak separation (18 peaks) was obtained in 20 min with an electric field of 350 V/cm. In addition, we have evaluated the stability of a coated capillary with poly-N,N-dimethylacrylamide (60/30 cm total/effective length and 75 microm ID) for over 100 runs of tryptic digest with the nonaqueous background electrolyte solvent system. The migration times for ten selected peptide peaks presented 3-7% relative standard deviation.     

Computer simulation for the convenient optimization of isocratic reversed-phase liquid chromatographic separations by varying temperature and mobile phase strength

The review summarizes the most recent developments in the field of enantioseparation of chiral drugs using capillary electromigration techniques. The basic principles of enantioseparations in CE are discussed. Recent developments in sample introduction, separation and detection in capillary electrophoresis and capillary electrochromatography are summarized. The applications are arbitrarily divided into the following three groups: (a) racemates and artificial mixtures of enantiomers, (b) drug forms and (c) chiral drugs and their metabolites in biological fluids. Among the various techniques involved the relatively new developments such as CEC in aqueous and nonaqueous buffers, on-line CE-MS coupling, etc. are emphasized.     

Recent progress in enantiomer separation by capillary electrochromatography

Enantiomer separation by electrochromatography (CEC) can be performed in three modes: (i) open-tubular capillary electrochromatography (o-CEC), in which the chiral selector is physically adsorbed coated, and thermally immobilized or covalently attached to the internal capillary wall; (ii) packed capillary electrochromatography (p-CEC), in which the capillary is either filled with chiral modified silica particles or with an achiral packing material, and a chiral selector is added to the mobile phase; and (iii) monolithic (rod)-capillary electrochromatography (rod-CEC) in which the chiral stationary phase (CSP) consists of a single piece of porous solid. We present an overview on methods and new trends in the field of electrochromatographic enantiomer separation such as CEC with either nonaqueous mobile phases or stationary phases with incorporated permanent charges, or with packing beds consisting of nonporous silica particles or particles with very small internal diameters.     

Nonaqueous capillary electrophoresis-mass spectrometry for separation of venlafaxine and its phase I metabolites

Aqueous and nonaqueous capillary electrophoresis (NACE) were investigated for separation of venlafaxine, a new second-generation antidepressant, and its three phase I metabolites. Working at basic pH, around the venlafaxine pKa value, was effective in resolving the investigated drugs, but created considerable peak tailing. To overcome electrostatic interactions between analytes and silanol groups, investigations were also carried out at acidic pH. However, despite the addition of up to 50% v/v of organic solvents (e.g., methanol or acetonitrile), complete separation of the studied compounds was not possible. NACE was found to be an appropriate alternative to resolve venlafaxine and its metabolites simultaneously. Using a conventional capillary (fused-silica, 64.5 cm length, 50 microm inner diameter), and a methanol-acetonitrile mixture (20/80 v/v) containing 25 mM ammonium formate and 1 M formic acid, complete resolution of these closely related compounds was performed in less than 3.5 min. Selectivity, efficiency and separation time were greatly affected by the organic solvent composition. As the electric current generated in nonaqueous medium was very low, the electric field was further increased by reducing the capillary length. This allowed a baseline resolution of venlafaxine and its three metabolities in 0.7 min. Selectivity was compared in aqueous and nonaqueous media in relation to the acid-base properties of the analytes as well as to the solvation degree. Finally, the method successfully coupled on-line to mass spectrometry with electrospray ionization interface allowed significant sensitivity enhancement.     

非水毛细管电泳法分离3种单磷酸腺苷及其应用研究

采用非水毛细管电泳方法对2’-AMP、3’-AMP和5’-AMP 3种单磷酸腺苷进行分离研究,考察了电泳溶液pH*值、非水介质、缓冲溶液对分离的影响。以含50%乙腈的Tris-H3BO3体系为缓冲溶液,在pH*10.0、压差进样(50 mbar,5 s)、柱温25℃、25 kV恒压下进行分离,在波长260 nm处负极检测,各组分可达到基线分离。在质量浓度为1～100 mg/L范围内,3种单磷酸腺苷的线性关系良好,平均回收率为88%～106%,RSD小于4%。该方法应用于核苷样品的测定,结果满意。     

Di-n-amyl L-tartrate-boric acid complex chiral selector in situ synthesis and its application in chiral nonaqueous capillary electrophoresis

A chiral selector, di-n-amyl L-tartrate-boric acid complex, was in situ synthesized by the reaction of di-n-amyl L-tartrate with boric acid in a nonaqueous background electrolyte (BGE) using methanol as the medium. And a new method of chiral nonaqueous capillary electrophoresis (NACE) was developed with the complex as the chiral selector. It has been demonstrated that the chiral selector is suitable for the enantioseparation of some β-blockers and β-agonists in NACE. Some chiral analytes that could not be resolved in aqueous microemulsion electrokinetic chromatography (MEEKC) with the same chiral selector obtained baseline resolutions in the NACE system. The enantioseparation mechanism was considered to be ion-pair principle and the nonaqueous system was more favorable for the ion-pair formation which is quite useful for the chiral recognition. The addition of a proper concentration of triethylamine into the BGE to control the apparent pH (pH*) enhanced the enantiomeric discrimination. In order to achieve a good enantioseparation, the effects of di-n-amyl L-tartrate and boric acid concentration, triethylamine concentration, applied voltage, as well as capillary length were investigated. Under the optimum conditions, all of the tested chiral analytes including six β-blockers and five β-agonists were baseline resolved.     

Nonaqueous capillary electrophoresis-mass spectrometry

Nonaqueous background electrolytes broaden the application of capillary electrophoresis displaying altered separation selectivity and interactions between analytes and buffer additives compared to aqueous background electrolytes. In addition, nonaqueous capillary electrophoresis (NACE) appears to be ideally suited for online coupling with mass spectrometry due to the high volatility and low surface tension of many organic solvents. Despite these advantages and an increasing use of nonaqueous background electrolytes in CE, coupling of NACE to mass spectrometry has not yet been applied very often to date. The present review summarizes the applications of online NACE-MS with regard to the analysis of drugs, stereoisomers, peptides, alkaloids, polymers and others. A brief discussion of solvent effects in NACE and pH of nonaqueous background electrolyte systems is also presented.     

Chiral separations by capillary electromigration techniques in nonaqueous media. II. Enantioselective nonaqueous capillary electrochromatography

A review on the advantages, peculiarities, and the potential of enantioselective capillary electrochromatography (CEC) in nonaqueous media is presented. Some fundamentals on CEC with particular focus on enantioselective CEC are discussed. The strategies, concepts, preferentially utilized chiral selectors and column technologies that have been utilized to succeed in highly efficient enantiomer separations by nonaqueous CEC are described thoroughly.     

非水溶液毛细管电泳

评述了非水溶液毛细管电泳的应用及发展，对非水溶液毛细管电泳的原理及应用情况作了简要叙述，有机试剂在毛细管电泳中的加入，扩大了分析物质的范围，以纯有机试剂作电泳介质，具有许多水溶液毛细管电不能比拟的优点。     

微量金属元素的毛细管电泳分析方法及应用

综述了毛细管电泳分析微量金属元素的基本原理、分离模式(CZE、MKEC、非水电泳、芯片分离等)、检测方法(紫外、荧光、化学发光、安培、电导、质谱联用技术)等的进展和该技术在环境、生物医学领域的研究与应用。引用文献94篇。     

Determination of xanthohumol in hops (Humulus lupulus L.) by nonaqueous CE

Xanthohumol (XN) is a prenylated chalcone with antimutagenic and anticancer activity from hops. A nonaqueous reverse polarity capillary electrophoretic method for the determination of XN in hop extract was developed and validated. The optimal parameters were a 64.5 cm long fused-silica capillary with 50 microm id at 25 degrees C; 30 kV negative voltage (anode at detector side of the capillary); nonaqueous buffer with 75 mM NaOH and 50 mM boric acid in methanol; hydrodynamical injection with 10 mbar for 40 s; and detection at 440 nm. XN, isoxanthohumol (IX), colupulone, adlupulone, and n-lupulone were well resolved on the electropherogram. The LOD for XN was 0.05 mg/L and RSD for peak area was below 3%. The amount of XN in different samples of hop pellets varied from 0.14 to 0.42%.     

Advances in the analysis of proteins and peptides by capillary electrophoresis with matrix-assisted laser desorption/ionization and electrospray-mass spectrometry detection

High throughput, outstanding certainty in peptide/protein identification, exceptional resolution, and quantitative information are essential pillars in proteome research. Capillary electrophoresis (CE) coupled to mass spectrometry (MS) has proven to meet these requirements. Soft ionization techniques, such as matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI), have paved the way for the story of success of CE-MS in the analysis of biomolecules and both approaches are subject of discussion in this article. Meanwhile, CE-MS is far away from representing a homogeneous field. Therefore the review will cover a vast area including the coupling of different modes of CE (capillary zone electrophoresis, capillary isoelectric foscusing, capillary electrochromatography, micellar electrokinetic chromatography, nonaqueous capillary electrophoresis) to MS as well as on-line preconcentration techniques (transient capillary isotachophoresis, solid-phase extraction, membrane preconcentration) applied to compensate for restricted detection sensitivity. Special attention is given to improvements in interfacing, namely addressing nanospray and coaxial sheath liquid design. Peptide mapping, collision-induced dissociation with subsequent tandem MS, and amendments in mass accuracy of instruments improve information validity gained from MS data. With 2-D on-line coupling of liquid chromatography (LC) and CE a further topic will be discussed. A special section is dedicated to recent attempts in establishing CE-ESI-MS in proteomics, in the clinical and diagnostic field, and in the food sector.     

Nonaqueous capillary electrophoresis with alcoholic background electrolytes: separation efficiency under high electrical field strengths

The effect of high voltage on capillary electrophoresis (CE) separations of anionic analytes in nonaqueous separation media was investigated. Methanol, ethanol, 1-propanol, and 1-butanol were tested as background electrolyte (BGE) solvents. Experiments were carried out with a laboratory-built CE instrument suitable for high-voltage separations. Potentials up to 60 kV were applied with reversed polarity to generate unusually high field strengths (e.g. 2000 Vcm-1) and so achieve fast and efficient separations. Highest separation efficiencies were obtained with propanol as BGE solvent, and the dependency of the efficiency on the separation voltage was more or less linear. With the other alcohols, separation efficiency decreased or remained roughly constant with increasing absolute voltage. The separation efficiencies are discussed in terms of longitudinal diffusion, Joule heating, and analyte interaction with the capillary wall. Capillary preconditioning had a varied effect on the separations in the different BGEs as the BGE and the conditioning process affected the electroosmotic flow (EOF) velocity and direction.     

Directed control of electroosmotic flow in nonaqueous electrolytes using poly(ethylene glycol) coated capillaries

Poly(ethylene glycol) (PEG)-coated capillaries exhibit unique properties in nonaqueous electrolytes. Immobilized PEG interacts significantly with different cations present in nonaqueous electrolytes. This can induce a positive surface charge on PEG-coated capillaries and results in an adjustable anodic electroosmotic flow (EOF) in nonaqueous electrolytes whereas a reduced cathodic EOF is observed in aqueous electrolytes. The EOF can reversibly be adjusted by the variation of the electrolyte constitution, namely the type of the solvent used and the nature and concentration of background cations. In methanol and especially in acetonitrile electrolytes the magnitude and also the direction of EOF is strongly dependent on the water content. Using different alkali metal cations, the EOF can be increased, reduced, or even reversed depending on the nature of the cation. The directed manipulation of EOF in methanolic electrolytes using PEG-coated capillaries was applied for optimization of nonaqueous capillary electrophoretic separations of acidic compounds with regard to reproducibility, resolution, and analysis time.