Recent developments in the separation of inorganic and small organic ions by capillary electrophoresis

Which method should I use for ion analysis, ion chromatography (IC) or capillary electrophoresis (CE)? In terms of actual theoretical plates CE has a clear-cut advantage. The separation ability of IC is adequate for many sample types, and many separation scientists feel that IC offers greater reliability and confidence than CE. However, IC is a more mature technique and there has been more time to solve problems such as peak tailing and to improve reproducibility. The two techniques should be viewed as complementary. A number of recent developments in ion analysis by CE are discussed. These include some simple ways to control electroosmotic flow and improve reproducibility, separation of isotopes, improved methods of indirect photometric detection, a new contactless conductivity detector, separation of ions at low pH, and in solutions of high salt content. Progress in a new technique called IC-CE will be described in which a soluble ion-exchange polymer is added to the capillary electrolyte to separate anions based on differences in both electrophoretic mobility and ion-exchange interactions.     

Nonaqueous and aqueous capillary electrophoresis of synthetic polymers

In this work, the use of capillary electrophoresis (CE) to analyze synthetic polymers is reviewed including works published till February 2004. The revised works have been classified depending on the CE mode (e.g., free solution capillary electrophoresis, capillary gel electrophoresis, etc.) and type of buffer (i.e., nonaqueous, aqueous and hydro-organic background electrolytes) employed to separate synthetic macromolecules. Advantages and drawbacks of these different separation procedures for polymer analysis are discussed. Also, physicochemical studies of complex polymer systems by CE are reviewed, including drug release studies, synthetic polyampholytes, dendrimers, fullerenes, carbon nanotubes and associative copolymers.     

Capillary electrophoresis of inorganic anions

This review deals with the separation mechanisms applied to the separation of inorganic anions by capillary electrophoresis (CE) techniques. It covers various CE techniques that are suitable for the separation and/or determination of inorganic anions in various matrices, including capillary zone electrophoresis, micellar electrokinetic chromatography, electrochromatography and capillary isotachophoresis. Detection and sample preparation techniques used in CE separations are also reviewed. An extensive part of this review deals with applications of CE techniques in various fields (environmental, food and plant materials, biological and biomedical, technical materials and industrial processes). Attention is paid to speciations of anions of arsenic, selenium, chromium, phosphorus, sulfur and halogen elements by CE.     

Use of 1-alkyl-3-methylimidazolium-based ionic liquids as background electrolytes in capillary electrophoresis for the analysis of inorganic anions

Separation of inorganic anions in CE is often a challenging task because the electrophoretic mobilities of inorganic anions are comparable to or even greater than the EOF mobility. In this study, we present the use of ionic liquids (ILs) as background electrolytes (BGEs) in CE of inorganic anions. The 1-alkyl-3-methylimidazolium-based ILs as BGEs dynamically coated the capillary wall and induced a reversed EOF. This allowed the anions to comigrate with the EOF and yielded a rapid separation. Increasing the alkyl chain length of the ILs and BGE concentration can significantly improve the separation resolution. With 40 mM 1-butyl-3-methylimidazolium tetrafluoroborate as BGE, good separations of five model anions (Br-, I-, NO2(-), NO3(-), and SCN-) were achieved in a range of buffer pH values. The separation efficiency was as high as 34 600-155 000, and the RSDs of the migration times were less than 0.8% (n = 5).     

Pharmacokinetic applications of capillary electrophoresis

This review briefly discusses the use of capillary electrophoretic (CE) methods for the investigations of different aspects of pharmacokinetics. In most investigations, CE was the method of choice because of its unique features, including high resolving power for chiral or metabolite separation, small sample volume for pediatric pharmacokinetics or for cell-based investigations, in situ microdialysis sampling for rapid eliminations, low UV wavelength detection for nonderivatized analytes, fast and simplified sample processing for existing methods that require tedious sample preparation, or as a second method for verifications. Moreover, instrumental aspects of CE-based assays for pharmacokinetic studies, such as different modes of CE methods for analyzing biological samples, sample stacking for increasing detection sensitivity, and coupling techniques with microdialysis and mass spectrometry, are also discussed in this review. Furthermore, the advantages and limitations of CE methods as well as the future outlook for pharmacokinetic studies are summarized.     

Separation of living and dead polymers in synthetic polypeptide mixtures by nonaqueous capillary electrophoresis using differences in ionization states

The complexity in the mechanisms of polymerization of N-carboxyanhydrides requires the development of new analytical techniques able to separate mixtures of synthetic polypeptides. This work focuses on the separation of poly(N(epsilon)-trifluoroacetyl-L-lysine) (PTLL) mixtures by nonaqueous capillary electrophoresis (CE). The main goal of this work was to find electrophoretic conditions that permit the separation and the quantification of the dead polymer families that were previously identified in the samples. The influence of the pH of the electrolyte on the selectivity of the separation was carefully investigated. The mechanisms of separation of the PTTLs are discussed as a function of their ionization state. The separations obtained on a noncovalently coated capillary were compared with those obtained on a fused-silica capillary. Finally, using two different electrolytes, it is possible to quantify the three families of PTLLs, namely, the living PTLLs, the dead PTLLs with N-formyl end group and the dead PTLLs with a carboxylic end group. These results confirm the importance of CE for the separation of synthetic organic polymers in nonaqueous electrolytes.     

The importance of capillary electrophoresis,capillary electrochromatography,and ion chromatography in separations of inorganic ions

The importance of capillary electrophoresis (CE), capillary electrochromatography (CEC), and ion chromatography (IC) in inorganic ion analyses is outlined. Methods for improving the reliability of the CE measurements are briefly described. Selectivity optimization in CE analyses of inorganic cations and anions is discussed. Using the Peakmaster program, CE system peaks (system zones, eigenmobilites) and some important CE parameters, such as effective mobilities, electromigration dispersion, indirect UV, and direct conductivity signals, are predicted and compared with experimental analyses.     

Polymeric ionic liquid as a background electrolyte modifier enhancing the separation of inorganic anions by capillary electrophoresis

A novel and easy method for the separation of inorganic anions by capillary electrophoresis using a polymeric ionic liquid (PIL), poly(1-vinyl-3-butylimidazolium bromide) as a background electrolyte modifier has been developed. The PIL has been proved to generate a reversed electroosmotic flow which reduces the analysis time and improves the separation significantly. Effects of the PIL concentration and buffer composition (pH and concentration) were evaluated on basis of the resolution and efficiency of the sample. Under optimum conditions, good separation of six model inorganic anions was achieved with high efficiency and excellent reproducibility within 3 min. The results obtained indicate that the combination of reversed EOF and the association between the analytes and the PIL on the capillary wall or BGE play a prominent role in the separation of anions. Therefore, the PIL presents a useful alternative for the BGE modifier in the study of inorganic anions by CE.     

Conductivity detection in capillary electrophoresis

Among electrochemical detection methods in capillary electrophoresis, conductometric methods are of specific interest for the determination of inorganic species. This is due to the fact that inorganic ions exhibit a high equivalent conductivity which corresponds to the analytical signal in conductivity detection. Indirect optical absorption methods, which are widely used in capillary electrophoretic ion analyses, become less sensitive with smaller capillary dimensions and thus have disadvantages in electrokinetic chip separation technologies.Conductivity detection for capillary electrophoresis is performed either through galvanic contact or in a contactless mode. Techniques using a galvanic contact of the sample ions with the measuring electrode are performed either on-capillary without decoupling of the separation high voltage, or off-capillary after grounding the separation voltage in order to avoid interferences. This technology is specifically important when a suppressor is used prior to detection. Most contactless methods use oscillometric techniques in order to obtain the analytical signal.This review discusses the theoretical and instrumental background of conductivity detection in capillary electrophoresis and reports on recent aspects and applications using conductometric detection methods for capillary zone electrophoresis.     

Analysis of agrochemicals by capillary electrophoresis

An increasing amount of articles using capillary electrophoresis as an investigation tool for pesticides and environmental pollutants were found over the last few years in analytical chemistry oriented journals. This review covers a wide literature range of the 1990s and concentrates on the analysis of organic agrochemicals (herbicides, fungicides, insecticides, acaricides, etc.) with capillary electrophoresis (capillary zone electrophoresis, micellar electrokinetic chromatography with CE-UV-visible or laser-induced fluorescence detection) as well as with the on-coming hyphenated techniques like capillary electrophoresis-electrospray ionization mass spectrometry. The principal preconcentration methods that allowed real sample analysis with CE are also briefly discussed. The pesticides, the separation methods, the used electrolytes, the detection types, the detection limits and the preconcentration methods were classified and presented in tabulated form as a rapid information tool.     

Development of ion chromatography and capillary electrophoresis methods for the determination of Li in Li–Al alloy

Two methods were developed for determination Li content in Li–Al alloy by employing ion chromatography (IC) and capillary electrophoresis (CE) without any prior separation of Al matrix. In absence of suitable certified reference material the two methods were used to validate each other. Using a high capacity column and a weaker eluent methane sulphonic acid, it was possible to separate Li in IC without eluting strongly retained Al. The method showed good precision and sensitivity and was extended for analysis of routine samples. In the case of CE using imidazole as co-ion, Li was detected in CE by indirect detection. In view of no interference from Al, samples were analyzed without any matrix separation. The CE method was used successfully for sample analysis and results were compared with IC results.     

Combining tissue extraction and off-line capillary electrophoresis matrix-assisted laser desorption/ionization Fourier transform mass spectrometry for neuropeptide analysis in individual neuronal organs using 2,5-dihydroxybenzoic acid as a multi-functional agent

In this study we report an improved protocol that combines simplified sample preparation and micro-scale separation for mass spectrometric analysis of neuropeptides from individual neuroendocrine organs of crab Cancer borealis. A simple, one-step extraction method with commonly used matrix-assisted laser desorption/ionization (MALDI) matrix, 2,5-dihydroxybenzoic acid (DHB), in saturated aqueous solution, is employed for improved extraction of neuropeptides. Furthermore, a novel use of DHB as background electrolyte for capillary electrophoresis (CE) separation in the off-line coupling of CE to MALDI-Fourier transform mass spectrometric (FT-MS) detection is also explored. The new CE electrolyte exhibits full compatibility with MALDI-MS analysis of neuropeptides in that both the peptide extraction process and MALDI detection utilize DHB. In addition, enhanced resolving power and improved sensitivity are also observed for CE-MALDI-MS of peptide mixture analysis. Collectively, the use of DHB has simplified the extraction and reduced the sample loss by elimination of homogenizing, drying, and desalting processes. In the mean time, the concurrent use of DHB as CE separation buffer and subsequent MALDI matrix offers improved spectral quality by eliminating the interferences from typical CE electrolyte in MALDI detection.     

Trace analysis of surfactants using chromatographic and electrophoretic techniques

Because of the widespread use, increased application of new formulations and immense impact on organisms and ecology surfactants are still in the focus of analytical chemistry. The development of methods with higher selectivity and lower detection limits is important to meet the requirements of greater responsibility for health of people and environment. Efficient separation methods, like HPLC, GC and CE, in combination with sensitive detection, like MS, are to be preferred over collective techniques which can suffer from interfering components. A review on trace analysis of ionic and neutral surfactants including sample preparation steps is presented, considering especially those methods which provide information about homologous and isomeric distribution of surfactant mixtures. Examples for the determination of linear alkylbenzene sulfonates in river water by HPLC and CE are discussed to show the capability of these methods for environmental analyses. As future trends increased applications of LC/MS (very high sensitivity) and also of CE (robustness and possibility for rapid method development) can be predicted.     

Approaches to enhancing the sensitivity of capillary electrophoresis methods for the determination of inorganic and small organic anions

One of the major problems facing the development of capillary electrophoresis (CE) is the relatively high limits of detection when compared to traditional high-performance liquid chromatographic (HPLC) methods. While the use of an alternative detector can offer better sensitivity, a more universal approach is sample preconcentration. Numerous on-line methods have been developed to improve the sensitivity of CE, and are based on electrophoretic principles, chromatographic principles, or a combination of both. This review will discuss all forms of on-line preconcentration methods for CE, with emphasis given to those that have shown particular merit when applied to inorganic and small organic anions.     

High resolution separation methods for the determination of intact human erythropoiesis stimulating agents. A review

Human erythropoietin (hEPO), a hormone involved in the formation of red blood cells, is a 30 kDa glycoprotein with a high carbohydrate content. The production of recombinant hEPO has made possible its widespread therapeutic use and its banned use in competition sports. Methods to analyze EPO and other erythropoiesis stimulating agents (ESAs) are necessary for the characterization and quality control of these biopharmaceuticals and also for doping control. In this paper, high resolution separation methods, namely high performance liquid chromatography (HPLC) and capillary electrophoresis (CE), with special attention to CE-coupled mass spectrometry, are reviewed. The usefulness of these techniques when applied in different modes to separate the glycoprotein isoforms, aggregates or excipients are detailed. In addition, sample preparation methods that have been applied to ESA samples for subsequent determination by HPLC or CE, as well as the potential compatibility of other preparation methods, are discussed. Applications of the HPLC and CE methods regarding regulatory considerations for biopharmaceuticals analysis, with emphasis on biosimilars, and doping control are also included. Finally, limitations of the present methods and their possible solutions are considered.     

Identification and determination of inorganic anions in real extracts from pre- and post-blast residues by capillary electrophoresis

Fast, selective, and sensitive analysis of inorganic anions is compulsory for the identification of explosives in post-blast or environmental samples. For the last twenty years, capillary electrophoresis (CE) has become a valuable alternative to ion chromatography (IC) for the analysis of inorganic-based explosives because of its low running costs and its simplicity of use. This article focuses on the development and validation of a CE method for the simultaneous analysis of 10 anions (chloride, nitrite, nitrate, thiosulphate, perchlorate, chlorate, thiocyanate, carbonate, sulphate, and phosphate) which can be found in post-blast residues, plus for the first time azide anion, possibly present in the composition of detonators, and the internal standard (formate) in 20 min total runtime. Intermediate precisions were 2.11% for normalized areas and 0.72% for normalized migration times. Limits of detection close to 0.5 ppm for all anions were obtained with the use of preconcentration techniques, thanks to a fast and simple sample preparation allowing the analysis of a large variety of matrices with the developed generic CE method. The matrix effects were statistically studied for the first time in the explosive field for different matrices, containing interfering anions and cations, sometimes at high levels. In fact, no significant matrix effect occurred (tests with blank matrix extracts of soil, cloth, glass, plastic, paper, cotton, and metal). Finally, analyses of real post-blast residues and real detonator extracts were performed. The CE results were compared with those obtained with the IC method used routinely and showed excellent correlation.     

Separation of anions by ion chromatography-capillary electrophoresis

Capillary electrophoresis (CE) with a water-soluble ion-exchange polymer in the background electrolyte is very efficient for the separation of organic and inorganic anions because the ion-exchange selectivity, as well as differences in electrophoretic mobility, can be used for separating sample ions. Poly(diallyldimethylammonium chloride) (PDDAC) was employed for this purpose. A very stable electroosmotic flow was obtained between pH 2.3 and 8.5 due to the strong adsorption of PDDAC onto the capillary wall. The effect of ion exchange on the migration of sample anions and their separation was controlled by varying the concentration of PDDAC, the concentration and the type of salt used in the CE background electrolyte. Addition of organic solvent (e.g., acetonitrile) could also modify the sample migration and the separation. Baseline separations were obtained for anions with very similar mobilities, such as bromide and iodide, naphthalenesulfonates, and bi- and tricarboxylic acids. Typical separation efficiencies were between 195,000 and 429,000 theoretical plates per meter. Ten replicate separations gave an average RSD of 1.0% for migration times of the sample anions studied. Excellent separations were obtained for a variety of samples, including a separation of 17 inorganic and organic anions in less than 6 min.     

Derivatization of inorganic ions in capillary electrophoresis

This review gives a short overview of the main approaches to the derivatization of inorganic ions in capillary electrophoresis (CE) with emphasis on the most recent works. Various derivatization procedures and detection methods are discussed. A brief account of their advantages and limitations is given. More specific areas such as microchip CE, simultaneous separation of anions and cations, and speciation analysis are also briefly discussed.     

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.     

不同缓冲体系对毛细管电泳法分离15种核苷类化合物效果的比较

对毛细管电泳法分离15种核苷类化合物所用的不同缓冲液体系进行了系统比较,确定不同模式毛细管电泳法分析多种核苷类化合物的最适合背景缓冲液体系(BGE)。分别以四硼酸钠、磷酸氢二钠、乙酸钠、碳酸氢钠、乙酸铵和乙二胺(DEA)为背景电解质,对毛细管区带电泳(CZE)、毛细管电泳-电喷雾飞行时间质谱(CE-ESI-TOF/MS)以及胶束电动毛细管电泳(MEKC)3种模式进行比较,并对其中几种优势缓冲体系进行了优化。结果表明,CZE模式下使用四硼酸钠和磷酸氢二钠缓冲体系无法同时分离15种核苷类化合物,因此只适用于分析核苷类化合物数量较少的样品。而使用含有2%丙酮的300 mmol/L DEA能完全分开15种核苷类化合物,且分辨率和峰形良好。MEKC模式下,以25 mmol/L磷酸氢二钠(添加70 mmol/L十二烷基磺酸钠(SDS))为缓冲盐的分离结果最佳,并且此方法能成功应用于海洋生物海葵中核苷类化合物的分离。CE-ESI-TOF/MS分析中,以20 mmol/L乙酸铵(pH 10.0)为背景电解质,正离子模式检测,15种核苷类化合物的质谱信号均良好,检测灵敏度明显优于文献中报道的使用DEA缓冲体系的结果。本研究阐明了不同缓冲体系对15种核苷类化合物分离的适用性,为毛细管电泳技术在复杂基质中多种核苷类化合物的分离方法中的应用奠定了基础。