Advances in capillary electrophoretically mediated microanalysis: an update

This review, as a continuation of an earlier report, gives an overview of recent developments, over the period from 2003 until now, in the use of capillary electrophoretic techniques for the in-line study of enzymatic reactions, derivatization, and chemical reactions. The article is divided into two parts: (i) in-line enzymatic reactions and (ii) in-line derivatization and chemical reactions. The first part introduces electrophoretically mediated microanalysis (EMMA) and discusses and illustrates the different modes of EMMA. A literature overview on enzymatic reactions is provided. The second part starts with an introduction of the procedures and the nomenclature used in the area of in-line derivatization and chemical reactions based on EMMA. Reported derivatization and chemical reaction procedures are discussed and summarized.     

Recent developments and applications of EMMA in enzymatic and derivatization reactions

This review provides systematic coverage of examples in the field of in-capillary electrophorecially mediated microanalysis (EMMA). The recent developments and applications in the time period up to mid 2011 have been described, as well as relevant older papers. The basic principles and modes of in-capillary assays have been demonstrated. An overview is also given of the various injection, separation and detection modes implemented in combination with EMMA. The review is presented in two parts mainly dealing with (i) enzymatic and (ii) derivatization or chemical reactions. Finally, the future trends of CE in performing and monitoring reactions have been drawn.     

Advances in capillary electrophoretically mediated microanalysis

Recent developments in the use of capillary electrophoretic techniques for the in-line study of enzyme reactions and derivatization protocols are reviewed. The article is divided into two parts: (i) in-line enzyme reactions and (ii) in-line derivatization. The first part introduces electrophoretically mediated microanalysis (EMMA) and discusses and illustrates the different modes of EMMA. A literature overview is provided, starting from 1996, and the investigated enzymes are classified into two tables based on the mode of engagement (i.e., continuous or transient) of the developed EMMA-based assay. The second part starts with an introduction of the procedures and the nomenclature used in the area of in-line derivatization protocols based on EMMA. Reported derivatization procedures are discussed and classified in tables, according to the functional group that is derivatized.     

A rapid and sensitive CE method with field-enhanced sample injection and in-capillary derivatization for selenomethionine metabolism catalyzed by flavin-containing monooxygenases

A rapid and sensitive electrophoretically mediated microanalysis method with field-enhanced sample injection (FESI) for in-capillary derivatization was developed to determine selenomethionine (SeMet) and selenomethionine selenoxide (SeOMet). Phthalic anhydride (PA) was selected as the derivatization reagent due to the fast reaction at room temperature and the stability of derivatives. The in-capillary derivatization was accomplished by electrophoretically mixing PA and sample plugs. PA reagent was introduced hydrodynamically into the capillary, whereas the sample solution was injected electrokinetically, thus allowing a selective preconcentration of the analytes by FESI. For FESI, the optimum sample solvent was 2 mM borate solution. The borate buffer was suitable for both in-capillary derivatization and separation of the derivatives. The combination of electrophoretically mediated microanalysis with FESI for in-capillary derivatization was successfully achieved with about 800-fold concentration sensitivity enhancement compared to direct CE-UV detection in the same setup. The present method is miniaturized and fully automated, which ensures the on-line derivatization, stacking, separation and detection in 10 min. Finally, the developed method was successfully applied to measure enzyme activities by analyzing the reaction mixtures of SeMet with human flavin-containing monooxygenases (FMO). The results showed that both FMO1 and FMO3, but not FMO5 could catalyze the Se-oxygenation of SeMet.     

Electrophoretically mediated microanalysis for in-capillaryelectrical cell lysis and fast enzyme quantification by capillary electrophoresis

In this study, a novel capillary electrophoresis (CE)-based enzymatic assay was developed to evaluate enzymatic activity in whole cells. β-Galactosidase expression was used as an example, as it is a biomarker for assessing replicative senescence in mammalian cells. It catalyzes the hydrolysis of para-nitrophenyl-β-d-galactopyranoside (PNPG) into para-nitrophenol (PNP). The CE-based assay consisted of four main steps: (1) hydrodynamic injection of whole intact cells into the capillary, (2) in-capillary lysis of these cells by using pulses of electric field (electroporation), (3) in-capillary hydrolysis of PNPG by the β-galactosidase—released from the lysed cells—by the electrophoretically mediated microanalysis (EMMA) approach, and (4) on-line detection and quantification of the PNP formed. The developed method was applied to Escherichia coli as well as to human keratinocyte cells at different replicative stages. Results obtained by CE were in excellent agreement with those obtained from off-line cell lysates which proves the efficiency of the in-capillary approach developed. This work shows for the first time that cell membranes can be disrupted in-capillary by electroporation and that the released enzyme can be subsequently quantified in the same capillary. Enzyme quantification in cells after their in-capillary lysis has never been conducted by CE. The developed CE approach is automated, economic, eco-friendly, and simple to conduct. It has attractive applications in bacteria or human cells for early disease diagnostics or insights for development in biology.

Kinetic study of gamma-glutamyltransferase activity by electrophoretically mediated microanalysis combined with micellar electrokinetic capillary chromatography

The use of capillary electrophoresis for the determination of gamma-glutamyltransferase (GGT) activity with gamma-glutamyl-p-nitroanilide (Glu-p-NA) as a substrate was investigated. The reaction velocity was quantified spectrophotometrically by the corrected peak area of the product p-nitroaniline (pNA) at 380 nm. Micelles composed of sodium deoxycholic acid were used in the background electrolyte in order to obtain a baseline separation between the substrate and the product. The presence of the micelles did not influence the enzymatic reaction. The electrophoretic system was used, not only for the separation and quantitation of the different reaction compounds but also for the in-capillary mixing of the enzyme and substrate plugs. This methodology is known as electrophoretically mediated microanalysis (EMMA). With the developed in-capillary activity assay an average Michaelis constant (K(M)) for GGT was calculated to be 2.09 mM (RSD = 7.3%, n = 3), a value consistent with previously reported values.     

Advances in Capillary Electrophoresis-Based Enzyme Assays

Capillary electrophoresis (CE) has become a flexible and accurate, high-efficiency analytical separation technique in many areas requiring only minute amounts of sample and chemicals. Thus, CE has also been recognized as a suitable technique to study enzymatic reactions including the determination of Michaelis–Menten kinetic data or the identification and characterization of inhibitors. The most often applied CE-based enzyme assay modes can be divided into two categories: (1) pre-capillary assays where incubations are performed offline followed by CE analysis of substrate(s) and/or product(s) and (2) in-capillary assays in which the enzymatic reaction and analyte separation are performed in the same capillary. In case of the in-capillary assays, the enzyme may be immobilized or in solution. The latter is also referred to as electrophoretically mediated microanalysis (EMMA), while in the case of immobilized enzyme the term immobilized enzyme reactor (IMER) is used. The present review summarizes the literature on CE-based enzyme assays published between January 2010 and April 2015. Immobilized enzyme reactors as well as microfluidic devices applied to the study of enzymatic activity will also be briefly addressed.

     

毛细管电泳序列分析技术用于在线酶分析研究进展

毛细管电泳技术具有操作简单、样品消耗量少、分离效率高和分析速度快等优势,不仅是一种高效的分离分析技术,而且已经发展成为在线酶分析和酶抑制研究的强有力工具。酶反应全程的实时在线监测,可以实现酶反应动力学过程的高时间分辨精确检测,以更准确地获得反应机制和反应速率常数,有助于更好地了解酶反应机制,从而更全面深入地认识酶在生物代谢中的功能。此外,准确、快速的在线酶抑制剂高通量筛选方法的发展,对加快酶抑制类药物的研发以及疾病的临床诊断亦具有重要意义。电泳媒介微分析法(EMMA)和固定化酶微反应器(IMER)是毛细管电泳酶分析技术中常用的在线分析方法。这两种在线酶分析法的进样方式通常为流体动力学进样和电动进样,无法实现酶反应过程中的无干扰序列进样分析。近年来,基于快速序列进样的毛细管电泳序列分析技术已经发展成为在线酶分析的另一种强有力手段,以实现高时间分辨和高通量的酶分析在线检测。该文从快速序列进样的角度,综述了近年来毛细管电泳序列分析技术在线酶分析的研究进展,并着重介绍了各种序列进样方法及其在酶反应和酶抑制反应中的应用,包括光快门进样、流动门进样、毛细管对接的二维扩散进样、流动注射进样、液滴微流...     

Study of enzyme kinetics of phenol sulfotransferase by electrophoretically mediated microanalysis

Electrophoretically mediated microanalysis (EMMA) was applied for the study of the kinetic parameters of the enzymatic reaction of phenol sulfotransferase SULT1A1 isoenzyme with 4-nitrophenol as a substrate. The SULT1A1 activity was determined by the quantitation of the product, 4-nitrophenyl sulfate, at 274 nm by using different injection and separation steps. This new approach solved the problem of the presence of the very strong inhibitor, adenosine 3',5'-bisphosphate (PAP), in the co-substrate solution (adenosine 3'-phosphate 5'-phosphosulfate, PAPS) which is unstable at room temperature. The inhibitor PAP was electrophoretically separated from the co-substrate PAPS before the injection of enzyme and substrate inside the capillary (and thus before their in-capillary encountering). With the developed in-capillary SULT1A1 activity assay an average Michaelis constant (Km) for 4-nitrophenol was calculated to be 0.84 microM, a value which is consistent with a previously reported value. Strong substrate inhibition (above a 4-nitrophenol concentration of 2.5 microM) was observed, and this is also in accordance with literature values.     

Sensitivity enhancement by on-line preconcentration and in-capillary derivatization for the electrophoretic determination of amino acids

This study describes an application of on-line preconcentration by large-volume stacking in combination with in-capillary derivatization for enhancing spectrophotometric detection sensitivity in capillary electrophoresis. The method is illustrated by an example dealing with the determination of amino acids with 1,2-naphthoquinone-4-sulfonate as a labelling agent. Samples are dissolved in water in order to create a stacking process based on differences in the conductivity between this medium and a concentrated running buffer. The in-capillary derivatization is accomplished following a sandwich procedure in which the sample is inserted between two segments of reagent. Amino acid derivatives are obtained and separated in a fused-silica capillary with a sodium borate electrolyte buffer using 2-propanol as an organic modifier. The method is applied to the analysis of amino acids in pharmaceutical and feed samples. A good concordance between the predicted values and those obtained with the standard method is observed, with overall quantification error below 5%. The proposed procedure allows the detection limits sensitivity to be enhanced in 1000-fold with respect to conventional precapillary derivatization.     

Strategies for in-capillary derivatization of amino acids in capillary electrophoresis using 1,2-naphthoquinone-4-sulfonate as a labeling reagent.

This paper examines the potentiality of in-capillary derivatization for improving the sensitivity of the spectrophotometric detection of amino acids in capillary zone electrophoresis. 1,2-Naphthoquinone-4-sulfonate was selected as the labeling agent of amino acids. The underivatized sample and the reagent solution segments are injected by pressure into the capillary prior to applying the running voltage. The corresponding derivatization reaction occurs inside the capillary once the potential is applied, as it induces mixing of the sample with the reagent. Several introduction modes consisting of tandem or sandwich configuration have been evaluated. These techniques result in a straightforward and automated way of carrying out a derivatization. Furthermore, in-capillary procedures may become much more attractive than conventional pre-capillary derivatization in terms of sensitivity and reproducibility. The optimum operation mode found consists of a sandwich system where the sample is injected in between two reagent segments. The method was applied to the determination of amino acids in feed samples. Results show a good concordance with those given by a standard amino acid analyzer.     

Chromatographic separation for domoic acid using a fragment imprinted polymer

A method for real-time visualisation of reactions performed in-capillary by the technique of electrophoretically mediated microanalysis (EMMA) is described, using a two dimensional imaging detection system. The UV absorbance detector is based on a complementary metal oxide semiconductor (CMOS) active pixel sensor. Imaging of analyte peaks absorbing at 200 nm and migrating over length of 14 mm in the capillary dimension allowed measurement of velocities and lengths of reactant and product zones. By contrast with use of single point detection, velocities of species generated by reaction anywhere within the capillary are readily measured with CMOS imaging: this is of particular benefit for EMMA experiments where reaction occurs during zone overlap. For the oxidation of glutathione by hydrogen peroxide, reaction times were varied over the range 0.5-20 s by changing voltages for electrokinetic injection and zone migration, and reactant and product peak areas were obtained for kinetic analysis of the reaction. The use of EMMA conditions with CMOS imaging allows the whole process of reaction, separation and quantification to be carried out in nanolitre volumes on-capillary in a single run on a time scale of less than 5 min.     

Capillary electrophoretic analysis of carbohydrates derivatized by in-capillary condensation with 1-phenyl-3-methyl-5-pyrazolone

Our previous papers on capillary electrophoresis (CE) have shown that samples can be derivatized in a capillary and the derivatives can be analyzed immediately after derivatization, provided that the derivatization reaction is so rapid as to complete in seconds. The present paper presents extended application of in-capillary derivatization to a much slower reaction such as the condensation of reducing carbohydrates with 1-phenyl-3-methyl-5-pyrazolone (PMP) which requires 30 min at 70 degrees C in pre-column derivatization by manual operation. It was necessary to first drive the introduced plugs of sample and reagent solutions to put them together at the entrance of the heated portion of a capillary, then to allow the superimposed plugs to react for a relevant period. We showed how to determine the introduction times of the sample and the reagent solutions as well as intermediate running buffer, the voltages to be applied for plug driving and product analysis, and the duration of voltage application, all of which are important for effective in-capillary derivatization. An example of the analysis of maltooligosaccharides by this technique is presented. It was shown that maltooligosaccharides were quantitatively derivatized with PMP in 35 min at 57 degrees C, and the derivatives could be analyzed in ca. 15 min by CE immediately after derivatization. Separation was satisfactory in 200 mM borate buffer, pH 8.2 containing sodium dodecyl sulfate to a concentration of 200 mM. Although the theoretical plate number, and accordingly the resolution, were significantly lower than the corresponding values in pre-capillary derivatization, reasonable reproducibility was ensured for both migration time (RSD 3.5% on average) and peak area (RSD less than 3%) under the optimized conditions. It is notable that sample amount could be lowered to the 10 fmol level, in contrast to the 10 pmol level in pre-capillary derivatization. In addition, since the technique employed here (the modified at-inlet technique of in-capillary derivatization) is easily automated, the established system will be highly beneficial for routine analysis of carbohydrates. Analysis by this technique was also shown to be useful for kinetic study of the derivatization reaction.     

In-capillary derivatization and laser-induced fluorescence detection for the analysis of organophosphorus pesticides by micellar electrokinetic chromatography

We developed a rapid and sensitive method using in-capillary derivatization and laser-induced fluorescence (LIF) detection for the fully automated analysis of organophosphorus pesticides (OPPs), including glufosinate, aminomethylphosphonic acid (AMPA) and glyphosate by micellar electrokinetic chromatography (MEKC). The potential of 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) as in-capillary derivatization reagent is described for the first time. The unique feature of this MEKC method is the capillary being used as a small reaction chamber. In in-capillary derivatization, the sample and reagent solutions were injected directly into the capillary by tandem mode, followed by an electrokinetic step to enhance the mixing efficiency of analytes and reagent plugs in accordance with their different electrophoretic mobilities. Standing a specified time for reaction, the derivatives were then immediately separated and determined. Careful optimization of the derivatization and separation conditions allowed the determination of glufosinate, AMPA and glyphosate with detection limits of 2.8, 3.6 and 32.2 ng/mL, respectively. These detection limits were comparable to those of 1.4, 1.9 and 23.8 ng/mL obtained from conventional pre-capillary derivatization. Furthermore, repeatability better than 0.40% for migration time and 3.4% for peak area, as well as shorter migration time, was obtained. The method was successfully applied to the analysis of spiked river water sample with satisfactory results.     

Dual injection capillary electrophoresis: foundations and applications

The state of the art of capillary electrophoresis (CE) approaches based on dual injection is here reported. Dual injection strategies have been proposed with three main objectives: (i) to provide information about reaction kinetics and/or related parameters, (ii) to perform in-capillary derivatization for improving separation and/or determination, (iii) to develop electrophoretic methods for the simultaneous analysis of anionic and cationic compounds. For the first two purposes, dual injection, which involves sample and reagent, can be realized either from the same end of the capillary (electrophoretically mediated microanalysis, EMMA) or from the two ends of the capillary (electroinjection analysis, EIA). The third objective, with dual injection of sample from the two ends of the capillary, takes advantage of moving cationic and anionic compounds with opposite directions. The foundations of each alternative, conditions necessary for working with them, restrictions, applications as well as perspectives are reviewed in order to establish the advantages, shortcomings, and convenience or no of their use in comparison to conventional CE.     

In-capillary derivatization and analysis of ephedrine and pseudoephedrine by micellar electrokinetic chromatography with laser-induced fluorescence detection

This paper describes an automatic rapid approach for in-capillary derivatization of ephedrine (E) and pseudoephedrine (PE) and subsequent sensitive determination of the derivatives by micellar electrokinetic chromatography (MEKC) with laser-induced fluorescence (LIF) detection using 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) as fluorescent reagent. The unique feature of this method is the capillary being used as a small reaction chamber, in which the sample, derivatization buffer and reagent solutions were injected directly into the capillary by tandem mode, followed by an electrokinetic step (5 kV, 15s) to enhance the mixing efficiency of analytes and reagent plugs. Standing a specified time of 1 min for reaction, the derivatives were then immediately separated and determined. Several parameters for in-capillary derivatization and subsequent MEKC separation were systematically investigated. Under these optimized conditions, a baseline separation of the two analytes was achieved within 10 min and the derivatization concentration limits of detection were found to be 4.8 ng mL(-1) for E and 1.6 ng mL(-1) for PE, respectively. The method was validated in terms of precision, linearity, accuracy and successfully applied for the determination of the two alkaloids in ephedra herb and its preparations.     

Electrophoretically mediated microanalysis

This review describes the existing developments in the use of the capillary electrophoretic microanalytical technique for the in-line study of enzyme reaction, electrophoretically mediated microanalysis (EMMA). The article is divided into a number of parts. After an introduction, the different modes, basic principle, procedure, and some mathematical treatments of EMMA methodology are discussed and illustrated. The applications of EMMA for enzyme assay and for non-enzymatic determination are summarized into two tables. In addition to classical capillary electrophoresis (CE) instrument EMMA, special emphasis is given to a relatively new technique: EMMA on CE microchip. Finally, conclusions are drawn.     

Speciation of chromium by in-capillary derivatization and electrophoretically mediated microanalysis

An electrophoretic method for chromium speciation analysis--as Cr(III) and Cr(VI)--based on in-capillary derivatization with 1,5-diphenylcarbazide (DPC) is here proposed. As Cr(III) does not react with DPC, it was oxidized also in-capillary to Cr(VI) by Ce(IV). For this purpose, a capillary electrophoresis (CE) mode called electrophoretically mediated microanalysis (EMMA) based on sequential injection of sample and reagents--namely, DPC, sample and Ce(IV)--was employed. The conditions of both reactions--Cr(III) oxidation and Cr(VI)-DPC derivatization--were optimized in order to quantify separately the Cr(VI)-DPC complex from the original Cr(VI) in the sample and that from oxidation of Cr(III) to Cr(VI). The electrophoretic conditions were independently optimized for variables influencing the resolution and those affecting sensitivity. The method thus developed was applied to the determination of Cr(III) and Cr(VI) in glass material, for which different sample preparation methods--namely, EPA method 3060A, ultrasound-assisted leaching and microwave-assisted digestion--were tested. Microwave-assisted digestion was found to be the best sample preparation alternative in terms of efficiency of the step--99.6 and 98.3% for Cr(VI) and Cr(III), respectively--and procedure time--20 min. The complete method was validated with the certified reference material BAM-S004.     

Field-amplified sample injection and in-capillary derivatization for sensitivity improvement of the electrophoretic determination of histamine

The feasibility of the combination of field-amplified sample injection (FASI) and in-capillary derivatization was explored for improving sensitivity of histamine in capillary electrophoresis (CE). Naphthalene-2,3-dicarboxaldehyde (NDA) was used as derivatization reagent. The reagent and sample was introduced by tandem mode. The derivatization was accomplished by at-inlet mode with standing time of 1.5 min. The combination of FASI and in-capillary derivatization was successfully achieved with about 400-fold concentration sensitivity enhancement compared to pre-capillary derivatization at the same set-up. The detection limit of concentration for histamine reached 1.25 x 10(-11) M by CE and fluorescence detection with S/N = 3. Parameters affecting FASI and in-capillary derivatization process including sample matrix, buffer concentration and reagent injection amount, were investigated.     

Estimation of sialic acid in a sialoglycan and a sialoglycoprotein by capillary electrophoresis with in-capillary sialidase digestion

An example of application of in-capillary derivatization for CE, obtained by using the throughout-capillary format, is presented. Introduction of a sialoglycan (N-acetylneuraminyllactose) or a sialoglycoprotein (bovine serum fetuin) sample to a running buffer (pH 5.0) containing N-acetylneuraminidase followed by application of a voltage resulted in the release of N-acetylneuraminic acid (NANA) which could be estimated by CE with UV detection. Two-step application of voltages (5 and 20 kV) was proved to be more effective for rapid estimation of the released NANA. This format (modified throughout-capillary format) allowed differential estimation of the NANA present in the sample as an impurity and the NANA released from the substrate at the picomol level, and thereby reliable micro assay of the sialidase activity. It also allowed estimation of the rate constant of this enzymatic reaction.