Sensitive analysis of [D-Pen2,5]enkephalin in rat serum by capillary electrophoresis and laser-induced fluorescence detection

Separation and determination of enkephalin-related peptides using capillary electrophoresis

CZE with UV-absorption detection has been used for the separation and determination of enkephalin-related peptides. The experimental conditions, such as pH and concentration of running buffer, applied voltage, injection method, and time, were investigated in detail. Excellent separation efficiency could be obtained for ten enkephalin-related peptides with a 50 microm (ID) x 58 cm capillary using sodium dihydrogen phosphate as the running buffer (pH 3.11) when 20 kV of applied voltage was used. The concentration detection limits were found to be in the range of 0.31-1.94 microg/mL (defined as S/N = 3). The proposed method has been applied to analyze the spiked cerebrospinal fluid (CSF) sample, and the results showed that CZE is a powerful technique for separation and detection of the above biological peptides.

Analysis and separation of enkephalin and dalargin analogues and fragments by capillary zone electrophoresis

Capillary zone electrophoresis (CZE) has been applied to qualitative and quantitative analysis and separation of synthetic analogues and fragments of enkephalins ([Leu5]enkephalin, H-Tyr-Gly-Gly-Phe-Leu-OH, [Met5]enkephalin, H-Tyr-Gly-Gly-Phe-Met-OH), and dalargin (H-Tyr-D-Ala-Gly-Phe-Leu-Arg-OH), biologically active peptides with morphin-like effects acting as ligands for the opiate receptors in the brain. These oligopeptides (dipeptides to hexapeptides) were analyzed as cations in two acidic background electrolytes (BGEs), BGE I (100mM H3PO4, 50mM Tris, pH 2.25), BGE II (100mM iminodiacetic acid, pH 2.30), and both as cations and anions in alkaline BGE IV (40 mM Tris, 40 mM Tricine, pH 8.10). Purity degrees of peptides, expressed in three different ways (relative peak height, relative peak area and relative corrected peak area), were determined by their CZE analyses in the above BGEs, and their values were compared with respect to the peak shapes and migration times of the main synthetic products and their admixtures. Selected analogues and fragments of enkephalins and dalargin were successfully separated by CZE in acidic isoelectric buffers, 100 and 200 mM iminodiacetic acid, pH 2.30 and 2.32, respectively. The effective electrophoretic mobilities at standard temperature 25 degrees C, and effective and specific charges of all analyzed peptides in the above three BGEs were determined. Correlation between effective electrophoretic mobility of the analyzed peptides and their charge and size (relative molecular mass) was investigated, which revealed different molecular shape of analyzed peptides in acidic and alkaline BGEs. In addition, the selected characteristics of the UV-absorption detector (noise, signal to noise ratio, sensitivity, and limits of detection and quantification) were determined.

Biomedical applications of capillary electrophoresis with laser-induced fluorescence detection

Capillary electrophoresis (CE) is a high-efficiency analytical technique that has had a great impact as a tool in biomedical research, clinical and forensic practice in the last ten years. Only in one of the applications, the DNA analysis, it has had an explosive exponential growth in the last few years. This impact is expressed in an enormous amount of CE articles and many reviews. The CE advantages with respect to other analytical techniques: the required very small sample volume, rapid analysis, great resolution power and low costs, have made this technique ideal for the analysis of a numerous endogenous and exogenous substances present in biological fluids. The different modes of CE have been coupled to different detection techniques such as UV-absorbance, electrochemical, mass spectrometry and laser-induced fluorescence detection (LIFD) to detect different nature and molecular size separated analytes. This review focuses mostly on the applications of CE-LIFD, to measure drugs and endogenous neuroactive substances such as amino acids and monoamines, especially in microdialysis samples from experimental animals and humans. CE-LIFD trends are discussed: automated faster analysis with capillary array systems, resolution power improvement, higher detection sensitivity, and CE systems miniaturization for extremely small sample volume, in order to make CE easier and affordable to the lab bench or the clinical bed.

Capillary electrophoretic analysis of proteins and peptides of biomedical and pharmacological interest

Capillary electrophoresis (CE) is an automated approach to electrokinetic separations that has had a deep impact in all fields of life sciences, including biomedical and biotechnological research and clinical and forensic practice. The present review highlights aspects of peptides and proteins separations, with particular emphasis on macromolecular analytes of biomedical interest. Among the various CE techniques available, a novel methodology is here illustrated consisting in separations in acidic, isoelectric buffers, which have the advantage of protonating the silica wall, thus minimizing interactions of proteinaceous material with the siliceous surface, while allowing delivery of high voltage gradients, due to their low conductivities. The review ends with applications of CE to the analysis of folding/unfolding/refolding/misfolding of proteins, a field which has deep implications in the biomedical arena, since it is connected to a host of disorders, such as prion protein diseases.

Analysis of cellular release using capillary electrophoresis and matrix assisted laser desorption/ionization-time of flight-mass spectrometry

In order to increase our understanding of the mechanisms of learning and memory in the central nervous system, it is necessary to know the neurotransmitters and neuromodulators used in the specific neuronal circuits under study. Methods have been developed to identify the peptides released from single neurons and neuronal clusters from the common neuronal model Aplysia californica. Specifically, solid-phase extraction (SPE), capillary electrophoresis (CE) and matrix assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) are combined for profiling neuropeptide releasates. A variety of combinations of SPE and CE were coupled off-line with MALDI-TOF-MS to reduce the high physiological salts, to concentrate the analytes, and to reduce the complexity of the mass spectra using separation. With these protocols, peptides and proteins up to 11000 Da were detected in releasates, offering a much wider mass range compared to direct MALDI analysis of the same releasates. A number of expected and unknown neuropeptides, including egg-laying hormone (ELH) and the partially processed delta/gamma-bag cell peptide were observed in the SPE-treated releasates from a single Aplysia-cultured bag cell neuron. However, by adding a CE separation after the SPE step preceding off-line MALDI-TOF-MS detection, the most complete neuropeptide profiles were obtained.

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.

Derivatization trends in capillary electrophoresis

This survey gives an overview of recent derivatization protocols, starting from 1996, in combination with capillary electrophoresis (CE). Derivatization is mainly used for enhancing the detection sensitivity of CE, especially in combination with laser-induced fluorescence. Derivatization procedures are classified in tables in pre-, on- and postcapillary arrangements and, more specifically, arranged into functional groups being derivatized. The amine and reducing ends of saccharides are reported most frequently, but examples are also given for derivatization of thiols, hydroxyl, carboxylic, and carbonyl groups, and inorganic ions. Other reasons for derivatization concern indirect chiral separations, enhancing electrospray characteristics, or incorporation of a suitable charge into the analytes. Special attention is paid to the increasing field of research using on-line precapillary derivatization with CE and microdialysis for in vivo monitoring of neurotransmitter concentrations. The on-capillary derivatization can be divided in several approaches, such as the at-inlet, zone-passing and throughout method. The postcapillary mode is represented by gap designs, and membrane reactors, but especially the combination of separation, derivatization and detection on a chip is a new emerging field of research. This review, which can be seen as a sequel to our earlier reported review covering the years 1991-1995, gives an impression of current derivatization applications and highlights new developments in this field.

Quantitative analysis of pharmaceutically active peptides using on-capillary analyte preconcentration transient isotachophoresis

An on-capillary adsorptive phase in combination with capillary electrophoresis (CE), frequently referred to as preconcentration CE, for quantitative analysis of low peptide concentrations was developed. The capillary containing the on-line analyte preconcentrator can be constructed within 5 min from commercially available extraction disks. These disks contain poly(styrenedivinylbenzene) adsorbent particles incorporated in a matrix of inert Teflon, creating a mechanically stable sorbent. Therefore, no frits are needed in the capillary to hold the stationary phase in place. Several parameters, such as the required minimal elution volume, required elution strength, sample application speed or ionic strength, and the capacity were investigated and special interest was given to the quantitative properties of the method. Instead of nL injections, volumes up to a least 25 microL are possible, yielding improvements in detection limits of 3-4 orders of magnitude. The observed limit of detection for both model peptides was 20 pg, corresponding to a 20 microL injection of a 1 ng/mL solution of both model peptides. Using low-wavelength UV detection, reproducibility and linearity in the low nanogram range were satisfactory. No influence of matrix salt concentrations was observed, extending the use of CE to all kinds of samples.

Comparison between transient isotachophoretic capillary zone electrophoresis and reversed-phase liquid chromatography for the determination of peptides in plasma

Low levels of peptide drugs in human plasma can be determined employing off-line solid-phase extraction, followed by capillary zone electrophoresis with UV detection. A bioanalytical procedure is presented, using gonadorelin and angiotensin II in human plasma as model compounds. The solid-phase extraction method, based on a weak cation exchange mechanism, is able to remove interfering endogenous components from the plasma sample, extract the model peptides quantitatively, and give a possibility of concentrating the sample at the same time. Transient isotachophoretic conditions were kept to increase the sample loadability by about two orders of magnitude. Up to about 70% of the capillary was filled with the reconstituted extract, whereafter the peptides were selectively concentrated during the first 15 min. Subsequently, the concentrated sample zones were separated under capillary zone electrophoresis conditions, showing the technique's high resolution. For the model cationic peptides (gonadorelin, angiotensin II) good linearity and reproducibility was observed in the 20-100 ng/mL concentration range. A more extensive washing procedure permits quantitation of gonadorelin at the 5 ng/mL level. In comparison with a liquid chromatography analysis, superior mass sensitivity and separation are obtained with the transient isotachophoretic capillary zone electrophoresis method. Moreover, in this case equivalent sensitivity is achieved when it is directly compared with a liquid chromatography method with UV detection, keeping in mind that 60 times more sample is needed for the latter method. A further gain in sensitivity can be obtained when the analysis is combined with native fluorescence detection, as is demonstrated by combining liquid chromatography separation with fluorescence detection.

Capillary electrophoresis of peptides

This article gives a review of the recent developments in capillary electrophoresis (CE) of peptides. New approaches to the theoretical description of electromigration behavior of peptides are described, and methodological aspects of CE separations of peptides such as selection of separation conditions, sample treatment, suppression of peptide adsorption to the capillary wall and specificities of CE separation modes are discussed. Progress in application of high performance detection schemes, namely laser-induced fluorescence and mass spectrometry, in peptide separations by CE is presented. Applications of different CE techniques, zone electrophoresis, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography and electrochromatography to peptide analysis, preparation and physicochemical characterization are demonstrated.

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.

Capillary electrophoresis as a versatile tool for the bioanalysis of drugs--a review

This review article presents an overview of current research on the use of capillary electrophoretic techniques for the analysis of drugs in biological matrices. The principles of capillary electrophoresis and its various separation and detection modes are briefly discussed. Sample pretreatment methods which have been used for clean-up and concentration are discussed. Finally, an extensive overview of bioanalytical applications is presented. The bioanalyses of more than 200 drugs have been summarised, including the applied sample pretreatment methods and the achieved detection limits.

Strategies for capillary electrophoresis: method development and validation for pharmaceutical and biological applications

This review is in support of the development of selective, reproducible and validated capillary electrophoretis (CE) methods. Focusing on pharmaceutical and biological applications, the successful use of CE is demonstrated by more than 800 references, mainly from 1994 until 1998. Approximately 80 recent reviews have been catalogued. These articles sum up the existing strategies for method development in CE, especially in the search for generally accepted concepts, but also looking for new, promising reagents and ideas. General strategies for method development were derived not only with regard to selectivity and efficiency, but also with regard to precision, short analysis time, limit of detection, sample pretreatment requirements and validation. Standard buffer recipes, surfactants used in micellar electrokinetic capillary chromatography (MEKC), chiral selectors, useful buffer additives, polymeric separation media, electroosmotic flow (EOF) modifiers, dynamic and permanent coatings, actions to deal with complex matrices and aspects of validation are collected in 20 tables. Detailed schemes for the development of MEKC methods and chiral separations, for optimizing separation efficiency, means of troubleshooting, and other important information for key decisions during method development are given in 19 diagrams. Method development for peptide and protein separations, possibilities to influence the EOF and how to stabilize it, as well as indirect detection are considered in special sections.