Capillary electrophoresis-mass spectrometry of basic proteins using a new physically adsorbed polymer coating. Some applications in food analysis

Selective detection of cytochrome C by microchip electrophoresis based on an aptamer strategy

The release of cytochrome C (Cyt C) plays an important role in apoptosis. In this study, selective and sensitive detection of Cyt C based on an aptamer strategy coupled with MCE was developed. Following the binding of a specific aptamer to Cyt C, the aptamer exhibited an irregular state, reducing the binding affinity of a fluorescent probe, and thus preventing the aptamer-Cyt C complexes from detection within the MCE. The height of the detection peak of the residual aptamer linearly decreased, and therefore, the difference in peak height of residual aptamer compared to that of the initial aptamer was used to quantify the captured protein concentration. Experimental conditions such as incubation time, pH, temperature, and ionic strength were optimized. A measurement of Cyt C concentration by MCE was achieved within 135 s, with a limit of detection as low as 0.4 nM. The proposed method has high selectivity and good stability for the detection of Cyt C. The experimental results demonstrate that this method is quick, consumes only a small quantity of sample, is highly selectivity and exhibits high sensitivity.

Capillary Electrophoresis in Wine Science

Capillary electrophoresis appeared to be a powerful and reliable technique to analyze the diversity of wine compounds. Wine presents a great variety of natural chemicals coming from the grape berry extraction and the fermentation processes. The first and more abundant after water, ethanol has been quantified in wines via capillary electrophoresis. Other families like organic acids, neutral and acid sugars, polyphenols, amines, thiols, vitamins, and soluble proteins are electrophoretically separated from the complex matrix.Here, we will focus on the different methodologies that have been employed to conduct properly capillary electrophoresis in wine analysis.Two examples informing on wine chemistry obtained by capillary electrophoresis will be detailed. They concern polyphenol analysis and protein profiling. The first category is a well-developed quantitative approach important for the quality and the antioxidant properties conferred to wine. The second aspect involves more research aspects dealing with microbiota infections in the vineyard or in the grape as well as enological practices.

Online Capillary IsoElectric Focusing-ElectroSpray Ionization Mass Spectrometry (CIEF-ESI MS) in Glycerol-Water Media for the Separation and Characterization of Hydrophilic and Hydrophobic Proteins

Capillary isoelectric focusing (CIEF) is a high-resolution technique for the separation of ampholytes, such as proteins, according to their isoelectric point. CIEF coupled online with MS is regarded as a promising alternative to 2-D PAGE for fast proteome analysis with high-resolving capabilities and enhanced structural information without the drawbacks of conventional slab-gel electrophoresis. However, online coupling has been rarely described, as it presents some difficulties. A new methodology for the online coupling of CIEF with electrospray ionization mass spectrometry (ESI-MS) has been developed in glycerol-water media. This new integrated methodology provides a mean for the characterization of a large number of hydrophilic and hydrophobic proteins.

Screening of Small Intact Proteins by Capillary Electrophoresis Electrospray Ionization-Mass Spectrometry (CE-ESI-MS)

Capillary electrophoresis (CE) has been shown to be a suitable separation technique for complex samples. Combined with electrospray ionization-mass spectrometry (ESI-MS), it is a powerful tool offering the opportunity of high selectivity and sensitivity combined with the possibility to identify and characterize intact proteins. In this protocol, we demonstrate a screening method for intact proteins based on capillary zone electrophoresis (CZE) separation coupled with online mass spectrometric detection. In order to avoid protein-wall interactions, a neutral coated capillary is used to create a universal method for proteins with both low and high electrophoretic mobilities. In addition, we show the successful validation and application of this screening method for a set of eight standard proteins and the glycoprotein erythropoietin.

Identification of allergenic milk proteins markers in fined white wines by capillary liquid chromatography-electrospray ionization-tandem mass spectrometry

A method based on capillary liquid chromatography combined with electrospray ionization-tandem mass spectrometry (CapLC-ESI-MS-MS) for the detection and identification of casein deriving peptides in fined white wine is described. This is the first step towards the development of a liquid chromatography mass spectrometric method for the detection/identification of markers of potentially allergenic milk proteins used as wine fining agents. The method demonstrated to be capable of detecting some peptides arising from alpha and beta casein (with the relative aminoacidic sequences elucidated) in extracts of white wine fined with casein at 100 and 1000 microg/mL. This MS based approach appears to be a useful tool for screening purposes as well as a confirmatory tool for the unequivocal identification of caseins in ELISA positive samples.

Online CIEF-ESI-MS in glycerol-water media with a view to hydrophobic protein applications

A new online coupling of CIEF with ESI-MS has been developed in glycerol-water media. This improved protocol provides: (i) the electric continuity during the whole analysis by a discontinuous filling of the capillary with 60:40 (cm/cm) catholyte/proteins-ampholyte mixture; (ii) the use of an anticonvective medium, i.e. 30:70 glycerol/water, v/v, compatible with MS detection and as an aid to hydrophobic protein solubilization and (iii) the use of unmodified bare fused-silica capillaries, as the glycerol/water medium strongly reduces EOF. Focusing was performed in positive polarity and cathodic mobilization was achieved by both voltage and pressure application. The setup was optimized with respect to analysis time, sensitivity and precision on pI determination. The optimized anolyte and catholyte were composed of 50 mM formic acid/1 mM glutamic acid (pH 2.35) and 100 mM NH(3)/1 mM lysine (pH 10.6), respectively. The effects of ampholyte concentration, focusing time and ESI parameters were presented for model proteins and discussed. This new integrated protocol should be an easy and effective additional tool in the field of proteome analysis, providing a means for the characterization of a large number of hydrophilic and hydrophobic proteins.

Recent food safety and food quality applications of CE-MS

The first on-line coupling of CE with MS detection more than 20 years ago provided a very powerful technique with a wide variety of applications, among which food analysis is of special interest, especially that dealing with food safety and food quality applications, the major topics of public interest nowadays. With this review article, we would like to show the most recent applications of CE-MS in both fields by recompiling and commenting articles published between January 2004 and October 2008. Although both applications are difficult to separate from each other, we have included in this work two main sections dealing with each specific field. Future trends will also be discussed.

Capillary electrophoresis-mass spectrometry as a powerful tool in biomarker discovery and clinical diagnosis: an update of recent developments

Proteome analysis has emerged as a powerful technology to decipher biological processes. One of the main goals is to discover biomarkers for diseases from tissues and body fluids. However, the complexity and wide dynamic range of protein expression present an enormous challenge to separation technologies and mass spectrometry (MS). In this review, we examine the limitations of proteomics, and aim towards the definition of the current key prerequisites. We focus on capillary electrophoresis coupled to mass spectrometry (CE-MS), because this technique continues to show great promise. We discuss CE-MS from an application point of view, and evaluate its merits and vices for biomarker discovery and clinical applications. Finally, we present several examples on the use of CE-MS to determine urinary biomarkers and implications for disease diagnosis, prognosis, and therapy evaluation.

The first contribution of capillary electrophoresis to the study of abiotic origins of homochirality: investigation of the enantioselective adsorption of 3-carboxy adipic acid on minerals

CE with UV detection was used for the first time to determine the enantioselective adsorption of the short-chain tricarboxylic acid, 3-carboxy adipic acid, on minerals as a mean of investigating plausible mechanisms for the origin of biochemical homochirality on Earth. The use of vancomycine as chiral selector in the separation buffer using the partial filling technique enabled the separation of the two enantiomers of this organic acid in about 12 min. Taking into account that this compound has a low absorption of the UV light, and in order to achieve the sensitivity needed to determine the enantiomeric excess of samples of 3-carboxy adipic acid adsorbed on minerals, we applied a strategy consisting of a field-amplified sample stacking together with the use of a bubble capillary and detection at low wavelength (192 nm). This combination enabled an LOD of about 10(-7) M and the determination of the enantiomeric excess of 3-carboxy adipic acid adsorbed on calcite and feldspar mineral samples at subnanomol levels of this acid. Results showed that an enantioselective adsorption of the enantiomers of 3-carboxy adipic acid on minerals took place.

Reproducible and efficient separation of aggregatable zein proteins by CZE using a volatile background electrolyte

Zein proteins are a complex mixture of polypetides that belong to the alcohol-soluble storage proteins group (prolamines) in corn. These proteins constitute about 50-60% of the total endosperm protein and are classified in different groups on the basis of differences in their solubility and sequence. Among them, zein proteins are considered the majority group showing a high tendency to aggregate what makes their analysis by any analytical method very difficult. Thus, CZE of these proteins requires the use of very complex BGEs noncompatible with online ESI-MS analysis. The aim of this work was to find a new BGE for the CZE separation of zein protein fully compatible with ESI-MS while providing further light on the complex CZE separation of aggregatable proteins. Thus, it is demonstrated in this work that efficient and reproducible CZE separations of zein proteins can be achieved by using a BGE composed of water, ACN, formic acid and ammonium hydroxide. Besides, it is shown that zein analysis is significantly improved by including the effect of an ammonium gradient during their separation. It is experimentally verified that the ammonium gradient can easily be achieved in CZE by either working with a sample zone with a low concentration of ammonium and a BGE with a high concentration, or conversely, working with a sample zone with high ammonium concentration and a BGE with low concentration of ammonium, giving rise in both cases to a significant improvement in the CZE separation of these proteins. It is demonstrated that this procedure can give rise to efficiency improvements of up to 20-fold in the CZE separation of zein proteins. Under optimized conditions, 20 proteins could be separated with average efficiencies higher than 400 000 theoretical plates/m. Some possible explanations of this effect are discussed including stacking, protein-capillary wall adsorption, protein solubility and protein-salt interactions.

Single-run separation of cationic, anionic, and polyanionic compounds by CE-ESI-MS

A method for a single-run separation of cationic, anionic, and polyanionic compounds by CE hyphenated to ESI MS (CE-ESI-MS) is described. One of the main issues for coupling CE to MS with an ESI source consists in maintaining an electric contact for the electrophoretic separation. This condition is only performed if a liquid flow arising from the separation capillary is directed to the needle, making it coupling-compatible. This latter situation is incompatible with the separations of polyanionic compounds of higher electrophoretic mobility (in absolute value) than the electroosmotic mobility, performed in bare fused-silica capillaries under a negative polarity. In this study, several alternative approaches were evaluated to circumvent this difficulty, and applied to the setup of the CE-MS separation of a mixture containing both cationic and polyanionic compounds, which are synthesis intermediates of contrast agents for medical imaging. Eventually, the detection of the cationic and anionic compounds in a single run could be obtained by either using neutrally coated polymethylsiloxane (DB-1) capillaries and simultaneously applying a negative voltage polarity and a pressure allowing to compensate for the residual cathodic EOF or by dynamically modifying the inner wall of a bare fused-silica capillary with a polycationic polymer (hexadimethrine bromide) and using it afterwards under negative voltage polarity.

Capillary electrophoresis–mass spectrometry for the analysis of intact proteins

Developments in the fields of protein chemistry, proteomics and biotechnology have increased the demand for suitable analytical techniques for the analysis of intact proteins. In 1989, capillary electrophoresis (CE) was combined with mass spectrometry (MS) for the first time and its potential usefulness for the analysis of intact (i.e. non-digested) proteins was shown. This article provides an overview of the applications of CE-MS within the field of intact protein analysis. The principles of the applied CE modes and ionization techniques used for CE-MS of intact proteins are shortly described. It is shown that separations are predominantly carried out by capillary zone electrophoresis and capillary isoelectric focusing, whereas electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) are the most popular ionization techniques used for interfacing. The combination of CE with inductively coupled plasma (ICP) MS for the analysis of metalloproteins is also discussed. The various CE-MS combinations are systematically outlined and tables provide extensive overviews of the applications of each technique for intact protein analysis. Selected examples are given to illustrate the usefulness of the CE-MS techniques. Examples include protein isoform assignment, single cell analysis, metalloprotein characterization, proteomics and biomarker screening. Finally, chip-based electrophoresis combined with MS is shortly treated and some of its applications are described. It is concluded that CE-MS represents a powerful tool for the analysis of intact proteins yielding unique separations and information.

Capillary electrophoresis–mass spectrometry of proteins at medium pH using bilayer-coated capillaries

The feasibility of using noncovalently bilayer-coated capillaries for capillary electrophoresis-mass spectrometry (CE-MS) of acidic proteins was investigated using background electrolytes (BGEs) of medium pH. The capillary was coated by successively rinsing the capillary with solutions of the oppositely charged polymers polybrene (PB) and poly(vinyl sulfonic acid) (PVS). Volatile BGEs containing ammonium formate and/or N-methyl morpholine were tested at pH 7.5 and 8.5. Overall, these BGEs provided relatively fast protein separations (analysis times of ca. 12 min) and showed high efficiencies (70,000-300,000 plates) when the ionic strength was sufficiently high. Migration-time reproducibilities were very favorable with RSDs of less than 1.0%. Infusion experiments showed satisfactory MS responses for studied proteins dissolved in ammonium formate (pH 8.5), however, high concentrations of N-methyl morpholine appeared to seriously suppress the MS protein signals. Evaluation of the CE-MS system was performed by analyzing a mixture of intact proteins yielding efficient separations and good-quality mass spectra. CE-MS analysis of a reconstituted formulation of the biopharmaceutical recombinant human growth hormone (rhGH) which was stored for a prolonged time, revealed one degradation product which was provisionally identified as desamido rhGH. Based on the MS responses the amount of degradation was estimated to be ca. 25%.

On-line CE-MS using pressurized liquid junction nanoflow electrospray interface and surface-coated capillaries

A simple and cost-effective laboratory-made liquid junction interface was used for coupling of CE with MS. In this device the capillary column and the spray tip were positioned in the electrode vessel containing appropriate spray liquid. The electrospray potential was applied on the electrode inside the liquid junction. A stable electrospray was produced at nanoliter per minute flow rates generated in the emitter tip without using an external pump. This arrangement provided high durability of the spray tip and independent optimization of the CE separation (use of coated capillaries) and ESI conditions. CE-MS analysis of mixtures of drugs, peptides, tryptic digests of proteins and biological fluids was optimized with respect to the effects of the distance between the separation capillary and electrospray tip and pressure applied on the liquid junction. The sensitivity of the system, in terms of the LOD (base peak monitoring) was below 10 ng/mL for the beta-blocker drugs and below 200 ng/mL for peptide analysis.

Sample treatments prior to capillary electrophoresis-mass spectrometry

Sample preparation is a crucial part of chemical analysis and in most cases can become the bottleneck of the whole analytical process. Its adequacy is a key factor in determining the success of the analysis and, therefore, careful selection and optimization of the parameters controlling sample treatment should be carried out. This work revises the different strategies that have been developed for sample preparation prior to capillary electrophoresis-mass spectrometry (CE-MS). Namely the present work presents an exhaustive and critical revision of the different samples treatments used together with on-line CE-MS including works published from January 2000 to July 2006.