On-line electrodialysis-capillary zone electrophoresis of adenosine triphosphate and inositol phosphates

The potential of electrophoretic sample pretreatment techniques and new instrumentation for bioanalysis, with a focus on peptidomics and metabolomics

This Review highlights the potential of new electromigration-based sample pretreatment techniques for bioanalysis. Sample pretreatment is a challenging part of the analytical workflow, especially in the fields of peptidomics and metabolomics, where the analytes are very diverse, both in physicochemical properties and in endogenous concentration. Electromigration-based techniques have several strengths, such as fast selective analyte concentration and that complementary information on the content of a sample can be obtained when compared with more conventional (chromatography-based) techniques. In the past decade, various new electromigration-based sample pretreatment techniques have been developed, and importantly, new instrumental setups. In this Review, we provide an introduction on electromigration and its strengths. Then, selected examples of electromigration-based sample pretreatment techniques and instrumentation are discussed, namely free-flow electrophoresis, isoelectric focusing, isotachophoresis, electrodialysis, electromembrane extraction and electroextraction. Finally, the promising perspectives of electromigration-based sample pretreatment techniques are outlined.

Capillary electrophoresis for monitoring bioprocesses

Chemical characterization and monitoring of fermentation broths and cell culture media provide significant information on the changes occurring within these complex and dynamic systems. Analytical methods based on CE in capillaries and microchips are attractive for integration in instrumental tools to obtain this critical data, improving the understanding and control of bioprocesses. In this review, the use of CE for chemical characterization and monitoring fermentations is discussed, organized by analyte class, including organic acids, pharmaceuticals, proteins, sugars, amino acids, and metabolites published between 1992 and October 2012. A section is dedicated to the roles CE plays throughout the wine making process, where applications range from characterization and increase in fundamental understanding of the fermentation to forensic applications, verifying the authenticity of the wine.

Capillary electrophoresis of signaling molecules

The emerging field of quantitative systems biology uses high-throughput bioanalytical measurements to gain a deeper understanding of biological phenomena. With the advent of instrumentation platforms, capillary electrophoresis spans a very wide range of biological applications. This short article focuses on the exploitation of capillary electrophoresis for the systems-level analysis of cell signaling molecules.

Electrokinetic migration across artificial liquid membranes

Basic drug substances were transported across a thin artificial organic liquid membrane by the application of 300 V d.c. From a 300 microl aqueous donor compartment (containing 10 mM HCl), the drugs migrated through a 200 microm artificial liquid membrane of 2-nitrophenyl octyl ether immobilized in the pores of a polypropylene hollow fiber, and into a 30 microl aqueous acceptor solution of 10 mM HCl inside the lumen of the hollow fiber. The transport was forced by an electrical potential difference sustained over the liquid membrane, resulting in electrokinetic migration of drug substances from the donor compartment to the acceptor solution. Within 5 min of operation at 300 V, pethidine, nortriptyline, methadone, haloperidol, and loperamide were extracted with recoveries in the range 70-79%, which corresponded to enrichments in the range 7.0-7.9. The chemical composition of the organic liquid membrane strongly affected the permeability, and may serve as an efficient tool for controlling the transport selectivity. Water samples, human plasma, and human urine were successfully processed, and in light of the present report, electrokinetic migration across thin artificial liquid membranes may be an interesting tool for future isolation within chemical analysis.

Determination of myo-inositol phosphates in food samples by flow injection-capillary zone electrophoresis

A capillary electrophoresis (CE) method with indirect photometric detection was developed to identify and quantify myo-inositol phosphates in food samples. A flow-injection (FI) system including a micro-column containing anionic exchange resin was used for the solid-phase extraction of the myo-inositol phosphates with a view to their preconcentration. The FI system was automatically coupled to CE equipment via a mechanical interface. The overall analysis time was shortened by incorporating an FI system for myo-inositol hexakisphosphate monitoring. The limit of detection for myo-inositol phosphates as determined by FI-CE ranged from 11 to 26 micromol/L and the coefficient of variation from 3.9 to 5.0%. On the other hand, the limit of detection and coefficient of variation for myo-inositol hexakisphosphate as monitored by the FI system were 75 micromol/L and 2.9%, respectively. The proposed method was successfully applied to a variety of food samples with recoveries ranging from 96.0 to 107.7% and the precision from 3.9 to 7.9%. Based on the results, the content of myo-inositol hexakisphosphate in nuts was two or three times higher than that in legumes.

On-line sample preconcentration in capillary electrophoresis, focused on the determination of proteins and peptides

This overview highlights the possibilities of on- or in-line preconcentration procedures in combination with a CZE separation, focused on the determination of peptides and proteins. The discussed methods, including sample stacking, field-amplified injection, isotachophoresis, solid phase extraction, membrane preconcentration, electroextraction, supported liquid membranes, hollow fibers, immunoaffinity, and molecularly imprinted polymers technology preconcentration are categorized in electrophoresis-based and chromatography-based preconcentration. The chromatography-based preconcentration is subdivided in low-specificity and high-specificity methods. A number of preconcentration methods are available, however, this paper demonstrates that various compounds in different media (aqueous solutions, urine, and plasma) require different preconcentration systems. The preconcentration techniques of first choice in general seem to be solid-phase extraction and membrane preconcentration, because of their high concentration ability, multiapplicability, relative simplicity and clean-up capability. For the future, hollow fibers seem to hold a great potential as preconcentration technique, yielding high concentration factors, using simple designs. New techniques, such as hollow fibers, molecularly imprinted polymers technology and supported liquid membranes may have the potential to supersede the conventional preconcentration techniques in some cases. The larger the arsenal of preconcentration techniques becomes, the more efficiently peptides and proteins may be analyzed in the future. These techniques, in some cases, require pre-cleanup procedures, to ensure the purity of the samples to concentrate.

Coupling continuous separation techniques to capillary electrophoresis

One of the weak points of capillary electrophoresis is the need to implement rigorously sample pretreatment because its great impact on the quality of the qualitative and quantitative results provided. One of the approaches to solve this problem is through the symbiosis of automatic continuous flow systems (CFSs) and capillary electrophoresis (CE). In this review a systematic approach to CFS-CE coupling is presented and discussed. The design of the corresponding interface depends on three factors, namely: (a) the characteristics of the CFS involved which can be non-chromatographic and chromatographic; (b) the type of CE equipment: laboratory-made or commercially available; and (c) the type of connection which can be in-line (on-capillary), on-line or mixed off/on-line. These are the basic criteria to qualify the hyphenation of CFS (solid-phase extraction, dialysis, gas diffusion, evaporation, direct leaching) with CE described so far and applied to determine a variety of analytes in many different types of samples. A critical discussion allows one to demonstrate that this symbiosis is an important topic in research and development, besides separation and detection, to consolidate CE as a routine analytical tool.

Advances in sample preparation in electromigration, chromatographic and mass spectrometric separation methods

The quality of sample preparation is a key factor in determining the success of analysis. While analysis of pharmaceutically important compounds in biological matrixes has driven forward the development of sample clean-up procedures in last 20 years, today's chemists face an additional challenge: sample preparation and analysis of complex biochemical samples for characterization of genotypic or phenotypic information contained in DNA and proteins. This review focuses on various sample pretreatment methods designed to meet the requirements for the analysis of biopolymers and small drugs in complex matrices. We discuss the advances in development of solid-phase extraction (SPE) sorbents, on-line SPE, membrane-based sample preparation, and sample clean-up of biopolymers prior to their analysis by mass spectrometry.

Analytical applications of membrane extraction in chromatography and electrophoresis

An overview of the analytical applications of membrane-based systems for sample enrichment in chromatography and capillary electrophoresis is presented. A brief introduction to the different types of membranes and the main forces related to the transport through them is also given.

Coupling of biological sample handling and capillary electrophoresis

The analysis of biological samples (e.g., blood, urine, saliva, tissue homogenates) by capillary electrophoresis (CE) requires efficient sample preparation (i.e., concentration and clean-up) procedures to remove interfering solutes (endogenous/exogenous and/or low-/high-molecular-mass), (in)organic salts and particulate matter. The sample preparation modules can be coupled with CE either off-line (manual), at-line (robotic interface), on-line (coupling via a transfer line) or in-line (complete integration between sample preparation and separation system). Sample preparation systems reported in the literature are based on chromatographic, electrophoretic or membrane-based procedures. The combination of automated sample preparation and CE is especially useful if complex samples have to be analyzed and helps to improve both selectivity and sensitivity. In this review, the different modes of solid-phase (micro-) extraction will be discussed and an overview of the potential of chromatographic, electrophoretic (e.g., isotachophoresis, sample stacking) and membrane-based procedures will be given.

Membrane-based sample preparation coupled on-line to chromatography or electrophoresis

A review on the use of membranes for on-line sample preparation prior to chromatographic and electrophoretic analysis is provided. The current state-of-the-art of four membrane-based techniques (dialysis, electrodialysis, filtration and membrane extraction) is described by reviewing their principles and applications. Possible future developments are discussed.

Developments in sample preparation and separation techniques for the determination of inorganic ions by ion chromatography and capillary electrophoresis

A review is presented of sample preparation and separation techniques for the determination of inorganic ions by ion chromatography (IC) and capillary electrophoresis (CE). Emphasis has been placed on those sample treatment methods which are specific to inorganic analysis, and the developments in separation methods which are discussed are those which enhance the capabilities of IC and CE to handle complex sample matrices. Topics discussed include solid-phase extraction for sample clean-up and preconcentration, dialytic methods, combustion methods, matrix-elimination IC, electrostatic IC, electrically polarised ion-exchange resins, electromigration sample preparation in CE, chromatographic sample preparation for CE, use of high-ionic strength background electrolytes, buffering of background electrolytes in CE, use of capillary electrochromatography for inorganic determinations, and methods for the manipulation of separation selectivity in both IC and CE. Finally, some possible future trends are discussed.

Affinity capillary electrophoresis coupled with on-line microdialysis by attachable electrode

This paper developed a new affinity capillary electrophoresis method coupled with on-line microdialysis using attachable electrodes in order to study the interaction of biomacromolecules with their small molecule ligands in the desired physiological conditions. The sampling mechanism was discussed and the experimental conditions were optimized. The affinity constant of sulfamethoxazole (SMZ) with bovine serum albumin (BSA) was determined with homemade equipment. The method is simple and practical.

Electrokinetic injection in capillary electrophoresis and its application to the analysis of inorganic compounds

In capillary electrophoresis, electrokinetic injection is a highly controversial sampling technique. It is a simple mode of sample introduction which is suitable for on-line preconcentration of the analytes, but its precision and accuracy are more strongly affected by experimental conditions compared to hydrodynamic injection. In the first part of this paper the features of electrokinetic and hydrodynamic injections are compared, followed by a detailed discussion on the different biases of electrokinetic injection and on how to reduce them. Finally, applications of the electrokinetic injection are reviewed with special emphasis on the analysis of inorganic compounds.

Analysis of nucleotides by capillary electrophoresis

Capillary electrophoresis is a useful tool for the analysis of nucleotides. Methods have been optimized for both CZE and MECC modes. A variety of CZE buffers, such as borate, carbonate and phosphate were used successfully. The pH of the buffer changes the charge on the nucleotides. Therefore, the selectivity of the analytes can be controlled by the acidity of the buffer solution. CE separations of nucleotides have been performed at all pH levels, in both CZE and MECC modes. SDS was the most commonly used modifier in MECC separations, but other additives have been added to optimize selectivity. In addition, nucleotides have been quantified in different matrices, including tissue and cell extracts and several DNA and RNA sources. This paper summarizes the methods used for the optimization of nucleotides by CE and includes the most recent techniques to improve selectivity, reproducibility and sensitivity. A summary of CE methods is used in analyses of nucleotides in biological matrices is included.