Applications of capillary electrophoresis with chemiluminescence detection in clinical,environmental and food analysis. A review

This paper reviews the latest developments and analytical applications of chemiluminescence detection coupled to capillary electrophoresis (CE-CL). Different sections considering the most common CL systems have been included, such as the tris(2,2?-bipyridine)ruthenium(II) system, the luminol and acridinium derivative reactions, the peroxyoxalate CL or direct oxidations. Improvements in instrumental designs, new strategies for improving both resolution and sensitivity, and applications in different fields such as clinical, pharmaceutical, environmental and food analysis have been included. This review covers the literature from 2010 to 2015.     

Flow-Based Methods with Chemiluminescence Detection for Food and Environmental Analysis: A Review

This paper presents an overview of flow-based methods in food and environmental analysis using chemiluminescence (CL) detection covering the period from 2005 to the present. The review discussses both automated flow methods of analysis [such as flow-injection analysis (FIA), sequential-injection analysis (SIA) and their variants] and separation techniques [liquid chromatography (LC) and capillary electrophoresis (CE) coupled to CL detection]. The most widely used CL reactions are presented together with representative applications in food and environmental analysis (determination of naturally occurring compounds, contaminants, additives as well as determination of inorganic and organic compounds).     

Dual‐signal amplification strategy for ultrasensitive chemiluminescence detection of PDGF–BB in capillary electrophoresis

Many efforts have been made toward the achievement of high sensitivity in capillary electrophoresis coupled with chemiluminescence detection (CE‐CL). This work describes a novel dual‐signal amplification strategy for highly specific and ultrasensitive CL detection of human platelet‐derived growth factor–BB (PDGF–BB) using both aptamer and horseradish peroxidase (HRP) modified gold nanoparticles (HRP–AuNPs–aptamer) as nanoprobes in CE. Both AuNPs and HRP in the nanoprobes could amplify the CL signals in the luminol–H₂O₂ CL system, owing to the excellent catalytic behavior of AuNPs and HRP in the CL system. Meanwhile, the high affinity of aptamer modified on the AuNPs allows detection with high specificity. As proof‐of‐concept, the proposed method was employed to quantify the concentration of PDGF–BB from 0.50 to 250 fm with a detection limit of 0.21 fm. The applicability of the assay was further demonstrated in the analysis of PDGF–BB in human serum samples with acceptable accuracy and reliability. The result of this study exhibits distinct advantages, such as high sensitivity, good specificity, simplicity, and very small sample consumption. The good performances of the proposed strategy provide a powerful avenue for ultrasensitive detection of rare proteins in biological sample, showing great promise in biochemical analysis. Copyright © 2015 John Wiley & Sons, Ltd.     

Light‐emitting‐diode‐induced chemiluminescence detection for capillary electrophoresis

In this work, an LED‐induced‐chemiluminescence (LED‐CL) system was developed to extend the application of CL detection in CE. In the LED‐CL, the analyte photooxidizes luminol under the irradiation of LEDs and generates CL. Taking the advantage of the small size nature of LEDs, the constructed photoreactor is greatly miniaturized, and especially suitable as a CE detector. The feasibility of the proposed detector was evaluated by detection of riboflavin (RF), flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) after CE separation. Under the optimized conditions, the LODs for RF, FMN and FAD were 0.007, 0.02 and 0.1 μg/mL, respectively, better than those by UV detection. The RSDs were 3.4, 3.6 and 4.1% for 0.5 μg/mL RF, 2 μg/mL FMN and 5 μg/mL FAD, respectively. The LED‐CL detector features low cost, miniaturization, fast response, high sensitivity and good reproducibility.     

An on-column fracture/end-column reaction interface for chemiluminescence detection in capillary electrophoresis

Chemiluminescence (CL) offers a sensitive detection method for capillary electrophoresis (CE), but the implementation of CE–CL is usually under compromised operating conditions for CE, such as the prerequisite of extreme pH buffer for optimal CL reaction at the capillary outlet. This has sometimes significantly deteriorated the separation of CE. In this study, the development of a new interface makes it possible to optimize the operating conditions for CE separation and CL detection independently. The interface consists of an on-column fracture being installed in a reservoir near the capillary end to create an electrical connection and also serve as reagent addition entrance. The capillary terminal is inserted into an end-column reservoir for CL reaction and detection. In this arrangement, the applied electric field has been decoupled from the CL detection, which is proved to effectively improve CE's performance by allowing the use of optimal CE buffers. At the same time, it enables the optimization of CL detection independently. The applicability of this interface was evaluated by using acridinium ester (AE) and luminol systems. For AE system, the interfering products of CL reagent (⁻OH, HO₂⁻) have been prevented, and the pH range of CE buffer can be independent to the optimal pH value of AE CL reaction, which is usually below 3. The AE was detected using running buffer at pH 8.7, giving a detection limit of 0.1 nM (S/N = 3), and the theoretical plate numbers is as high as 56 000. The on-column fracture based configuration is simple, sensitive and easy to implement.     

毛细管电泳与化学发光检测联用方法的研究进展

毛细管电泳由于其超高的分离效率广泛应用于生物医药、环境监测、食品科学以及公共安全等领域。然而,由于毛细管电泳具有进样量较少、检测光程较短等缺点,需要与高灵敏度检测器联用实现低浓度样品的分析。化学发光检测由于其背景信号低而具有超高的灵敏度。毛细管电泳-化学发光检测联用方法将毛细管电泳的高效分离特性与化学发光检测的高灵敏性相结合,成为一种非常重要的分析方法,广泛用于化学分析、药物筛选以及环境监测等领域。该文对近年来毛细管电泳-化学发光检测联用方法的基本原理进行概述,并对其发展趋势和应用前景进行了展望。     

Efficient recovery of electrophoretic profiles of nucleoside metabolites from urine samples by multivariate curve resolution

Chemometric techniques usually employed in purity assessment and resolution of multicomponent peaks have been applied to analytical data from complex biological samples obtained with CE‐DAD. In the assessment of the purity of the electrophoretic peaks, the orthogonal projection approach, the orthogonal projection approach with Durbin–Watson criterion, and the simple‐to‐use interactive self‐modeling mixture analysis method have been employed. Multivariate curve resolution with alternating least squares has been successfully implemented to resolve co‐migrating peaks of metabolites in CE‐DAD and to recover qualitative and quantitative information about co‐migrating components of urine extract. The main challenge consisted of developing high‐quality multivariate curve resolution with alternating least squares models of multicomponent peaks acquired during the CE analysis of nucleoside patterns in 18 urine samples. The recovered ultraviolet visible (UV–Vis) spectra have been employed to identify additional nucleosides, such as 1‐methylinosine, 2‐methylguanosine, and 1‐methylguanosine, whose presence in the metabolic profile produced by the applied CE‐DAD method has not yet been recognized. Concentration profiles of these compounds can be used in metabonomic studies.     

Use of capillary electrophoresis with chemiluminescence detection for sensitive determination of homocysteine

A sensitive capillary electrophoresis (CE) method with chemiluminescence (CL) detection was developed for the determination of homocysteine (HCys) in human plasma. In this work, N‐(4‐aminobutyl)‐N‐ethylisoluminol was used as tagging reagent to label the analyte for achieving high assay sensitivity. N‐(4‐Aminobutyl)‐N‐ethylisoluminol‐tagged HCys after CE separation reacted with hydrogen peroxide in the presence of horseradish peroxidase, producing CL emission. Experimental conditions for labeling analyte, CE separation, and CL detection were studied. The CL intensity was proportional to the concentration of HCys in the range of 2.5×10^?8 to 5.0×10^?6 M. Detection limit (S/N=3) was 7.6×10^?9 M. Human plasma samples from healthy donors were analyzed by the presented method. HCys levels were found to be in the range of 9.50–15.3 μM.     

The next generation of capillary electrophoresis instruments: Performance of CE‐SDS protein analysis

Over the last decade, capillary electrophoresis gained tremendous importance, because it became an indispensible tool for the quality control of biologics, e.g. therapeutic antibodies. Consequently, there has been a continuous development within the CE market. Microchip techniques have been established in the last years. Further trends are complete solutions for specific applications by the usage of reagent kits. Step by step instructions and facilitated handling of the instruments are becoming more common. This work focuses on the sized‐based protein analysis with CE‐SDS. The instruments CE 7100 by Agilent Technologies, LabChip® GXII Touch HT by PerkinElmer, Maurice S. by Protein Simple and PrinCE NextI870 by Prince Technologies have been evaluated, mainly analyzing protein mixtures of different molecular weights in long series. Published data of the PA 800 plus by SCIEX are also included in the tabled results. Precision, reliability, flexibility, and speed have been identified as the most important performance parameters, others such as resolution, sensitivity, linearity, ease of use and sustainability have also been considered. All tested instruments have shown an excellent performance. Depending on application and necessities, each user can find the most appropriate one.     

Evaluation of clarithromycin lactobionate as a novel chiral selector for enantiomeric separation of basic drugs in capillary electrophoresis

Nowadays, macrocyclic antibiotics are presenting an increasing number of enantioseparation applications. The macrocyclic antibiotics used as chiral selectors in capillary electrophoresis (CE) include the ansamycins and the glycopeptides. The macrolides, another important class of macrocyclic antibiotics, have been reported as a new type of chiral selectors recently. In this study, clarithromycin lactobionate (CL), belonging to the group of macrolide antibiotics, was first investigated for its potential as a novel chiral selector in CE for enantiomeric separation of several basic drugs. As observed, CL allowed excellent separation of the enantiomers of metoprolol, atenolol, propranolol, bisoprolol, esmolol, ritodrine, and amlodipine, as well as partial enantioresolution of labetalol and nefopam. In addition, CL possesses advantages such as high solubility and low viscosity in the solvent and very weak UV absorption. In the course of this study, it was found that both migration times and enantioseparation of the basic drugs were influenced by several experimental parameters, e.g. selector concentration, the composition and pH of the BGE, the type and concentration of organic modifier, and applied voltage. Thus, the effects of these factors were systematically investigated, and satisfactory enantioseparations of the studied drugs were achieved at the buffer pH range of 7.3–7.5 using 12.5 mM borax buffer with 50% v/v methanol, 60 mM CL, and 20 kV applied voltage. Moreover, comparison of the influences of the studied parameters was further investigated by means of Statistical Product and Service Solutions (SPSS) in this article.     

A 2‐D‐HPLC‐CE platform coupled to ESI‐TOF‐MS to characterize the phenolic fraction in olive oil

A 2‐D‐HPLC/CE method was developed to separate and characterize more in depth the phenolic fraction of olive oil samples. The method involves the use of semi‐preparative HPLC (C18 column 250×10 mm, 5 μm) as a first dimension of separation to isolate phenolic fractions from commercial extra‐virgin olive oils and CE coupled to TOF‐MS (CE‐TOF‐MS) as a second dimension, to analyze the composition of the isolated fractions. Using this method, a large number of compounds were tentatively identified, some of them by first time, based on the information concerning high mass accuracy and the isotopic pattern provided by TOF‐MS analyzer together with the chemical knowledge and the behavior of the compounds in HPLC and CE. From these results it can be concluded that 2‐D‐HPLC‐CE‐MS provides enough resolving power to separate hundreds of compounds from highly complex samples, such as olive oil. Furthermore, in this paper, the isolated phenolic fractions have been used for two specific applications: quantification of some components of extra‐virgin olive oil samples in terms of pure fractions, and in vitro studies of its anti‐carcinogenic capacity.     

Gold nanoparticle‐enhanced capillary electrophoresis‐chemiluminescence assay of trace uric acid

A sensitive method based on gold nanoparticle‐enhanced CE‐chemiluminescence (CL) detection was developed for quantifying uric acid (UA) in serum. In this work, gold nanoparticles were added into the running buffer of CE to catalyze the post‐column CL reaction between luminol and hydrogen peroxide, achieving highly efficient CL emission. Negative peaks were produced due to the inhibitory effects on CL emission from UA eluted from the electrophoretic capillary. The decrease in CL intensity was proportional to the concentration of UA in the range of 2.5×10^?7–1.0×10^?5 M. Detection limit was 4.6×10^?8 M UA. Ten human serum samples were analyzed by the presented method. Serum level of UA was found to be in the range from 204 to 324 μM for healthy subjects (n=5), and from 464 to 497 μM for diabetic patients (n=5). The two groups were significantly different (p<0.05). The results suggested a potential application of the proposed assay in rapid primary diagnosis of diseases such as diabetes.     

Recent advances in enrichment techniques for trace analysis in capillary electrophoresis

CE is gaining great popularity as a well‐established separation technique for many fields such as pharmaceutical research, clinical application, environmental monitoring, and food analysis, owing to its high resolving power, rapidity, and small amount of samples and reagents required. However, the sensitivity in CE analysis is still considered as being inferior to that in HPLC analysis. Diverse enrichment methods and techniques have been increasingly developed for overcoming this issue. In this review, we summarize the recent advances in enrichment techniques containing off‐line preconcentration (sample preparation) and on‐line concentration (sample stacking) to enhancing sensitivity in CE for trace analysis over the last 5 years. Some relatively new cleanup and preconcentration methods involving the use of dispersive liquid–liquid microextraction, supercritical fluid extraction, matrix solid‐phase dispersion, etc., and the continued use and improvement of conventional SPE, have been comprehensively reviewed and proved effective preconcentration alternatives for liquid, semisolid, and solid samples. As for CE on‐line stacking, we give an overview of field amplication, sweeping, pH regulation, and transient isotachophoresis, and the coupling of multiple modes. Moreover, some limitations and comparisons related to such methods/techniques are also discussed. Finally, the combined use of various enrichment techniques and some significant attempts are proposed to further promote analytical merits in CE.     

碳纳米管在分离科学中的应用研究进展

碳纳米管(CNTs)作为一种新型纳米材料已在材料、催化、吸附分离等诸多领域得到了广泛的应用。本文对近年来CNTs在分离科学中的应用研究进展进行了简要评述,主要讨论了CNTs在固相萃取、固相微萃取、膜萃取、色谱固定相和毛细管电泳假固定相等方面的应用。     

Capillary electrophoresis chemiluminescent detection system equipped with a two-step postcolumn flow interface for detection of some enkephalin-related peptides labeled with acridinium ester

Despite its low equipment cost and simple design, as one of the sensitive detectors for CE, the chemiluminescence (CL) detector was less developed compared to the detectors of MS and LIF. The main reasons were the limitation of CL reagents, the repeatability problems and the relatively low sensitivity compared to LIF. In this paper, a highly sensitive CE-CL detection system was developed for detection of some enkephalin-related peptides labeled with acridinium ester. A new detection interface was designed for CE with CL detection of acridinium ester and its labeled analytes. The interface included two sections: one was used to acidify the capillary outflow so that the corresponding acridinium pseudo-base form can be changed into acridinium ester form by adding excess acid to the system; the other was designed to provide a suitable solution to produce the CL from acridinium ester. The effect factors, such as pH, the concentration of reaction reagents and the flow rates of the reagents, were investigated. The results showed that acridinium ester had similar CL properties in this interface when pH values of CE BGE were changed from 2.0 to 10.8. The interface was used to detect acridinium ester and three acridinium ester-labeled enkephalin-related peptides, the corresponding LODs were found to be in the attomole range. This CL detection system proved to be of high sensitivity, good repeatability, and relatively low cost.     

Ionic liquids in enhancing the sensitivity of capillary electrophoresis: Off‐line and on‐line sample preconcentration techniques

The popularity of ionic liquids (ILs) has grown during the last decade in enhancing the sensitivity of CE through different off‐line or on‐line sample preconcentration techniques. Water‐insoluble ILs were commonly used in IL‐based liquid phase microextraction, in all its variants, as off‐line sample preconcentration techniques combined with CE. Water‐soluble ILs were rarely used in IL‐based aqueous two phase system (IL‐ATPS) as an off‐line sample preconcentration approach combined with CE in spite of IL‐ATPS predicted features such as more compatibility with CE sample injection due to its relatively low viscosity and more compatibility with CE running buffers avoid, in some cases, anion exchange precipitation. Therefore, the attentions for the key parameters affecting the performance of IL‐ATPSs were generally presented and discussed. On‐line CE preconcentration techniques containing IL‐based surfactants at nonmicellar or micellar concentrations have become another interesting area to improve CE sensitivity and it is likely to remain a focus of the field in the endeavor because of their numerous to create rapid, simple and sensitive systems. In this article, significant contributions of ILs in enhancing the sensitivity of CE are described, and a specific overview of the relevant examples of their applications is also given.     

Chemiluminescence detection coupled to capillary electrophoresis

In recent years, chemiluminescence (CL)-based detection coupled to capillary electrophoresis (CE) as separation technique has attracted much interest due to new advances in home-made configurations, sample-treatment techniques for application to real matrixes, development of a commercial instrument and use of miniaturization techniques to obtain micro total analysis systems incorporating CE separation and CL detection in microchips. We present some developments, key strategies and selected analytical applications of CE-CL since the year 2000 in diverse fields (e.g., clinical and pharmaceutical, environmental or food analysis).     

Yolk‐Shell Porous Microspheres of Calcium Phosphate Prepared by Using Calcium L‐Lactate and Adenosine 5′‐Triphosphate Disodium Salt: Application in Protein/Drug Delivery

A facile and environmentally friendly approach has been developed to prepare yolk‐shell porous microspheres of calcium phosphate by using calcium L ‐lactate pentahydrate (CL) as the calcium source and adenosine 5′‐triphosphate disodium salt (ATP) as the phosphate source through the microwave‐assisted hydrothermal method. The effects of the concentration of CL, the microwave hydrothermal temperature, and the time on the morphology and crystal phase of the product are investigated. The possible formation mechanism of yolk‐shell porous microspheres of calcium phosphate is proposed. Hemoglobin from bovine red cells (Hb) and ibuprofen (IBU) are used to explore the application potential of yolk‐shell porous microspheres of calcium phosphate in protein/drug loading and delivery. The experimental results indicate that the as‐prepared yolk‐shell porous microspheres of calcium phosphate have relatively high protein/drug loading capacity, sustained protein/drug release, favorable pH‐responsive release behavior, and a high biocompatibility in the cytotoxicity test. Therefore, the yolk‐shell porous microspheres of calcium phosphate have promising applications in various biomedical fields such as protein/drug delivery.     

Recent advances in capillary electrophoretic migration techniques for pharmaceutical analysis (2013–2015)

This review updates and follows‐up a previous review by highlighting recent advancements regarding capillary electromigration methodologies and applications in pharmaceutical analysis. General approaches such as quality by design as well as sample injection methods and detection sensitivity are discussed. The separation and analysis of drug‐related substances, chiral CE, and chiral CE‐MS in addition to the determination of physicochemical constants are addressed. The advantages of applying affinity capillary electrophoresis in studying receptor–ligand interactions are highlighted. Finally, current aspects related to the analysis of biopharmaceuticals are reviewed. The present review covers the literature between January 2013 and December 2015.     

Recent advances in capillary electrophoresis‐mass spectrometry: Instrumentation,methodology and applications

Capillary electrophoresis (CE) offers fast and high‐resolution separation of charged analytes from small injection volumes. Coupled to mass spectrometry (MS), it represents a powerful analytical technique providing (exact) mass information and enables molecular characterization based on fragmentation. Although hyphenation of CE and MS is not straightforward, much emphasis has been placed on enabling efficient ionization and user‐friendly coupling. Though several interfaces are now commercially available, research on more efficient and robust interfacing with nano‐electrospray ionization (ESI), matrix‐assisted laser desorption/ionization (MALDI) and inductively coupled plasma mass spectrometry (ICP) continues with considerable results. At the same time, CE‐MS has been used in many fields, predominantly for the analysis of proteins, peptides and metabolites. This review belongs to a series of regularly published articles, summarizing 248 articles covering the time between June 2016 and May 2018. Latest developments on hyphenation of CE with MS as well as instrumental developments such as two‐dimensional separation systems with MS detection are mentioned. Furthermore, applications of various CE‐modes including capillary zone electrophoresis (CZE), nonaqueous capillary electrophoresis (NACE), capillary gel electrophoresis (CGE) and capillary isoelectric focusing (CIEF) coupled to MS in biological, pharmaceutical and environmental research are summarized.