State-of-the-art of the hyphenation of capillary electrochromatography with mass spectrometry

Research advances based on mass spectrometry for profiling of triacylglycerols in oils and fats and their applications

Vegetable oils and animal fats are dietary source of lipids that play critical and multiple roles in biological function. Triacylglycerols (TAGs) are the principal component of oils and fats with significant difference in profile among different oils and fats. TAG profiling is essential for nutritional evaluation, quality control and assurance of safety in oils and fats. However, analysis of TAGs is a challenging task because of the complicated composition of TAGs and their similar physicochemical properties in oils and fats. The rapid development of mass spectrometry (MS) technology in recent years makes it possible to analyze the composition, content and structure of TAGs in the study of the physical, chemical and nutritional properties of oils, fats and related products. This review described the research advancement based on MS for profiling of TAGs in oil, fat and their applications in food. The application of MS, including direct infusion strategies, and its combination with chromatography, gas chromatography-MS (GC-MS) and liquid chromatography-MS (LC-MS), in the analysis of TAGs were reviewed. The advantages and disadvantages of these analytical methods with relevant applications for TAGs analysis in food were also described.

Enantioseparations of pharmaceuticals with capillary electrochromatography: A review

The chiral separation of pharmaceuticals is one of the major research topics in the pharmaceutical industry. Chromatographic techniques are most frequently used in this context. Separations in capillary electrochromatography (CEC) are an alternative and achieved by chromatographic retention and electrophoretic mobility principles. As a result, CEC is characterized by a high selectivity and efficiency. The limited number of stationary phases specifically developed for CEC, the low number of commercially available CEC columns, the frits to maintain the stationary phase, which forms fragile spots in the columns, and the limited column robustness and reproducibility, make CEC not very attractive for industrial application. However, CEC is still applied and studied in the academic field. This review discusses the enantioseparation of drugs in CEC published during the last four years, with a critical view on the reproducibility and the practical utility of these applications.

Monoliths in capillary electrochromatography and capillary liquid chromatography in conjunction with mass spectrometry

Here, we have reviewed separation studies utilizing monolithic capillary columns for separation of compounds preceding MS analysis. The review is divided in two parts according to the used separation method, namely CEC and capillary LC (cLC). Based on our overview, monolithic CEC-MS technique have been more focused on the syntheses of highly specialized and selective separation phase materials for fast and efficient separation of specific types of analytes. In contrast, monolithic cLC-MS is more widely used and is often employed, for instance, in the analysis of oligonucleotides, metabolites, and peptides and proteins in proteomic studies. While poly(styrene-divinylbenzene)-based and silica-based monolithic capillaries found their place in proteomic analyses, the other laboratory-synthesized monoliths still wait for their wider utilization in routine analyses. The development of new monolithic materials will most likely continue due to the demand of more efficient and rapid separation of increasingly complex samples.

Analytical tools for the analysis of β-carotene and its degradation products

β-Carotene, the precursor of vitamin A, possesses pronounced radical scavenging properties. This has centered the attention on β-carotene dietary supplementation in healthcare as well as in the therapy of degenerative disorders and several cancer types. However, two intervention trials with β-carotene have revealed adverse effects on two proband groups, that is, cigarette smokers and asbestos-exposed workers. Beside other causative reasons, the detrimental effects observed have been related to the oxidation products of β-carotene. Their generation originates in the polyene structure of β-carotene that is beneficial for radical scavenging, but is also prone to oxidation. Depending on the dominant degradation mechanism, bond cleavage might occur either randomly or at defined positions of the conjugated electron system, resulting in a diversity of cleavage products (CPs). Due to their instability and hydrophobicity, the handling of standards and real samples containing β-carotene and related CPs requires preventive measures during specimen preparation, analyte extraction, and final analysis, to avoid artificial degradation and to preserve the initial analyte portfolio. This review critically discusses different preparation strategies of standards and treatment solutions, and also addresses their protection from oxidation. Additionally, in vitro oxidation strategies for the generation of oxidative model compounds are surveyed. Extraction methods are discussed for volatile and non-volatile CPs individually. Gas chromatography (GC), (ultra)high performance liquid chromatography (U)HPLC, and capillary electrochromatography (CEC) are reviewed as analytical tools for final analyte analysis. For identity confirmation of analytes, mass spectrometry (MS) is indispensable, and the appropriate ionization principles are comprehensively discussed. The final sections cover analysis of real samples and aspects of quality assurance, namely matrix effects and method validation.

CEC-ESI ion trap MS of multiple drugs of abuse

This article describes a method for the separation and determination of nine drugs of abuse in human urine, including amphetamines, cocaine, codeine, heroin and morphine. This method was based on SPE on a strong cation exchange cartridge followed by CEC-MS. The CEC experiments were performed in fused silica capillaries (100 microm x 30 cm) packed with a 3 mum cyano derivatized silica stationary phase. A laboratory-made liquid junction interface was used for CEC-MS coupling. The outlet capillary column was connected with an emitter tip that was positioned in front of the MS orifice. A stable electrospray was produced at nanoliter per minute flow rates applying a hydrostatic pressure (few kPa) to the interface. The coupling of packed CEC columns with mass spectrometer as detector, using a liquid junction interface, provided several advantages such as better sensitivity, low dead volume and independent control of the conditions used for CEC separation and ESI analysis. For this purpose, preliminary experiments were carried out in CEC-UV to optimize the proper mobile phase for CEC analysis. Good separation efficiency was achieved for almost all compounds, using a mixture containing ACN and 25 mM ammonium formate buffer at pH 3 (30:70, v/v), as mobile phase and applying a voltage of 12 kV. ESI ion-trap MS detection was performed in the positive ionization mode. A spray liquid, composed by methanol-water (80:20, v/v) and 1% formic acid, was delivered at a nano-flow rate of approximately 200 nL/min. Under optimized CEC-ESI-MS conditions, separation of the investigated drugs was performed within 13 min. CEC-MS and CEC-MS(2) spectra were obtained by providing the unambiguous confirmation of these drugs in urine samples. Method precision was determined with RSDs values <or=3.3% for retention times and <or=16.3% for peak areas in both intra-day and day-to-day experiments. LODs were established between 0.78 and 3.12 ng/mL for all compounds. Linearity was satisfactory in the concentration range of interest for all compounds (r(2)>or=0.995). The developed CEC-MS method was then applied to the analysis of drugs of abuse in spiked urine samples, obtaining recovery data in the range 80-95%.

[Recent advances in capillary electrochromatography and its coupling techniques]

As a novel micro-separation technique, capillary electrochromatography (CEC) has the merits of high efficiency, high selectivity, high resolution and rapid analysis. However, the small-volume injection manipulated in capillary dimensions poses a great challenge for detectors in achieving high sensitivity. Currently, one of the major researches into CEC involves the development of some sensitive detection modes. The general introduction, which includes the historical perspectives and the principles of CEC, is briefly described. The recent advances about CEC coupled with various detectors and its applications in the separation of complex samples are summarized. A total of 141 references are reviewed.

CEC: selected developments that caught my eye since the year 2000

During the last decade, a number of new developments have emerged in the field of CEC. This paper focuses only on monolithic columns prepared from synthetic polymers. Monolithic columns have become a well-established format of stationary phases for CEC immediately after their inception in the mid-1990s. They are readily prepared in situ from liquid precursors. Also, the control over both porous properties and surface chemistries is easy to achieve. These advantages make the monolithic separation media an attractive alternative to capillary columns packed with particulate materials. Since the number of papers concerned with just this single topic of polymer-based monolithic CEC columns is large, this overview describes only those approaches this author found interesting.

Sequence Analysis of Native Oligosaccharides Using Negative ESI Tandem MS

Carbohydrates exhibit many physiologically and pharmacologically important activities, yet their complicated structure and sequence pose major analytical challenges. Although their structural complexity makes analysis of carbohydrate difficult, mass spectrometry (MS) with high sensitivity, resolution and accuracy has become a vital tool in many applications related to analysis of carbohydrates or oligosaccharides. This application is essentially based on soft ionization technique which facilitates the ionization and vaporization of large, polar and thermally labile biomolecules. Electrospray-ionization (ESI), one of the soft ionization technique, tandem MS has been used in the sequencing of peptides, proteins, lipids, nucleic acids and more recently carbohydrates. The development of the ESI and tandem MS has begun to make carbohydrate analysis more routine. This review will focus on the application of the ESI tandem MS for the sequence analysis of native oligosaccharides, including neutral saccharides with multiple linkages, and the uronic acid polymers, alginate and glycosaminoglycans structures containing epimers.

Analysis of proteins in solution using affinity capillary electrophoresis

Analysis of protein interactions by means of capillary electrophoresis (CE) has unique challenges and rewards. The choice of analysis conditions, especially involving electrophoresis buffers, are crucial and not universal for protein analysis. If conditions for analysis can be worked out, it is possible to utilize CE quantitatively and qualitatively to characterize protein-ligand binding involving unmodified molecules in solution and taking place under physiological conditions. This chapter deals with the most important practical considerations in capillary electrophoretic affinity approaches, affinity CE (ACE). The text emphasizes the most critical factors for successful analyses and has application examples illustrating various types of information offered by ACE-based studies. Also included are step-by-step accounts of the two main classes of experimental design: the pre-equilibration ACE (in the form of CE-frontal analysis (CE-FA)) and mobility shift ACE together with examples of their use. The ACE approaches for binding assays of proteins should be considered when the biological material is scarce, when any kind of labeling is not possible or desired, when the interacting molecules are the same size and when rapid and simple method development is a priority.

Packed-column capillary electrochromatography and capillary electrochromatography-mass spectrometry using a lithocholic acid stationary phase

The preparation and characterization of a novel lithocholic acid (LCA)-based liquid crystalline (LC) stationary phase (SP) suitable for application in packed-column CEC and CEC coupled to MS is described. The extent of bonding reactions of LCA-SP was assessed using 1H-NMR, 13C-NMR and elemental analysis. This characterization is followed by application of the LCA-SP for separation of beta-blockers, phenylethylamines (PEAs), polyaromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). Using the optimum mobile phase operating conditions (pH 3.0-4.5, 10 mM ammonium acetate, 85% v/v ACN), a comparison of the chromatographic ability of the aminopropyl silica phase vs. the LCA-bonded phase was conducted. The results showed improved selectivity for all test analytes using the latter phase. For example, the CEC-MS of beta-blockers demonstrated that the LCA-bonded phase provides separation of six out of seven beta-blockers, whereas the amino silica phase provides four peaks of several co-eluting beta-blockers. For the CEC-MS analysis of PEAs, the LCA-bonded phase showed improved resolution and different selectivity as compared to the aminopropyl phase. An evaluation of the retention trends for PEAs on both phases suggested that the PEAs were retained based on varying degree of hydroxyl substitution on the aromatic ring. In addition, the MS characterization shows several PEAs fragment in the electrospray either by loss of an alkyl group and/or by loss of H2O. Finally, the LCA-bonded phase displayed significantly higher separation selectivity for PAHs and PCBs as compared to the amino silica phase.

Capillary electrochromatography and on-line concentration

Capillary electrochromatography (CEC) is a micro-separation technique that combines the advantages of capillary zone electrophoresis with those of high-performance liquid chromatography. Accordingly, it has attracted extensive attention over the last decade. Among the stationary phases for CEC, monolithic stationary phase has been regarded as the most suitable stationary phase for CEC because of its simple preparation, the elimination of frits, and its excellent performance. In this chapter, procedures for preparing CEC monolithic columns with an improved configuration, in which there are stationary phases at both sides of detection window and no stationary phase at detection window, are presented. The separation of acidic and basic compounds on such monolithic columns is used as an example to demonstrate CEC separation protocol. Additionally, an on-line concentration technique in CEC is presented. As a result of the coexistence of stationary phase and electric field in a CEC column, it is possible to employ chromatographic zone sharpening and field-amplified sample stacking effects simultaneously to improve CEC detection sensitivity.

CEC and EKC of natural compounds

In this review, an overview of CEC and EKC methods with their developments are summarized for different natural compounds. It is divided into three main parts. The first part elaborates the separation of lipophilic compounds without any charged groups. The second part constitutes CEC and EKC of lipophilic compounds containing ionizable functional groups whereas the third part contains hydrophilic compounds. Packed, monolithic, coated, or raw fused-silica (FS) capillaries are among the choice for stationary phases. Applications of these phases on the above-mentioned three classes of compounds, coupled with different detection methods, e.g. MS or LIF, are explored and their advantages and disadvantages are discussed.

CEC separation of heterocyclic amines using methacrylate monolithic columns

Two methacrylate-based monolithic columns, one with a negatively charged group (sulfonic group) and another with a new monomer N,N-dimethylamino ethyl acrylate (DMAEA), were prepared and tested for the separation of basic compounds by CEC. This new monolithic stationary phase was prepared by the in situ polymerization of DMAEA with butyl methacrylate and ethylene dimethacrylate, using a ternary porogenic solvent consisting of water, 1-propanol and 1,4-butanediol. The performance of this column was evaluated by means of the analysis of a family of heterocyclic amines. Separation conditions such as pH, amount of organic modifier, ionic strength and elution mode (normal or counterdirectional flow) were studied. At the optimal running electrolyte composition, and using the counterdirectional mode, symmetrical electrochromatographic peaks were obtained, with the number of theoretical plates up to 30,000 and a good resolution between closely related peaks. The 2-acrylamido-2-methyl-1-propane-sulfonic acid column was used for CEC-MS, taking advantage of the compatibility of its elution mode (normal flow) with the MS coupling.

Capillary electrochromatography-mass spectrometry of cationic surfactants

The CEC-MS of alkyltrimethylammonium (ATMA+) ions with chain lengths ranging from C1-C18 is optimized using an internally tapered column packed with mixed mode reversed phase/strong cation exchange stationary phase. A systematic study of the CEC separation parameters is conducted followed by evaluation of the ESI-MS sheath liquid and spray chamber settings. First, the optimization of CEC separation parameters are performed including the ACN concentration, triethylamine (TEA) content, buffer pH and ammonium acetate concentration. Using 90% v/v ACN with 0.04% v/v TEA as mobile phase, the separation of longer chain C6-C18-TMA+ surfactants could be achieved in 15 min. Lowering the ACN concentration to 70% v/v provided resolution of shorter chain C1, C2-TMA+ from C6-TMA+ although the total analysis time increased to 40 min. Furthermore, variation of both the ACN and TEA content as well as ionic strength has found to significantly influence the retention of longer chain surfactants as compared to shorter chains. The optimum CEC conditions are 70% v/v ACN, 0.04% v/v TEA, pH 3.0 and 15 mM ammonium acetate. Next, the optimization of the ESI-MS sheath liquid composition is conducted comparing methanol to isopropanol followed by the use of experimental design for analysis of spray chamber parameters. Overall, the developed CEC-ESI-MS method allows quantitative and sensitive monitoring of ATMA+ from < or =10 microg/mL down to 10 ng/mL. Utilizing the optimized CEC-ESI-MS protocol, the challenging analysis of commercial sample Arquad S-50 ATMA+ containing cis-trans unsaturated and saturated soyabean fatty acid derivatives is demonstrated.

Simultaneous enantioseparation and sensitive detection of eight beta-blockers using capillary electrochromatography-electrospray ionization-mass spectrometry

The feasibility of using vancomycin chiral stationary phase (CSP) and polar organic eluent is investigated for simultaneous enantioseparation of eight beta-blockers using CEC coupled to ESI mass spectrometric detection (ESI-MS). The internally tapered capillaries were utilized to pack CEC-MS columns. As compared to externally tapered columns, the use of internally tapered columns demonstrated enhanced stability, durability, and reproducibility. A mixture containing methanol/ACN/acetic acid/triethylamine at 70:30:1.6:0.2 v/v/v/v was considered as optimum mobile phase since it provided a good compromise between resolution and analysis time. As expected, sheath liquid and ESI-MS parameters mainly influenced the detection sensitivity. Interestingly, structural information of beta-blockers was available by varying the MS fragmentor voltage using in-house CID in the scan mode. In order to maximize the chiral/achiral resolution, various column-coupling approaches using teicoplanin as complementary CSP to vancomycin were tested. Several changes in the elution order of beta-blockers were observed using multimodal CSPs with some improvement in chiral or achiral resolution. The quantitative aspects of the CEC-MS method were demonstrated using R- and S-talinolol as internal standards. The calibration curves of beta-blockers showed good linearity in the range of 3-600 microM. The enantiomer of beta-blockers at a concentration of 30 nM was detectable. Furthermore, both 0.1 and 1% of the S-enantiomer could be precisely quantified in the presence of 99.9 and 99% of the R-isomer of beta-blocker.

Capillary Electrochromatography Coupled to Atmospheric Pressure Photoionization Mass Spectrometry for Methylated Benzo[a]pyrene Isomers

Benzo[a]pyrene, one of the most carcinogenic PAHs, has 12 monomethylated positional isomers (MBAPs). A strong correlation between the carcinogenicity of these isomers and methyl substitution has been reported. In this study, on-line coupling of capillary electrochromatography (CEC) and atmospheric pressure photoionization mass spectrometry (APPI-MS) provides a unique solution to highly selective separation and sensitive detection of MBAP isomers. The studies indicated that APPI provides significantly better sensitivity compared to electrospray ionization and atmospheric pressure chemical ionization modes of MS. A systematic investigation of APPI-MS detection parameters and CEC separation is established. First, several sheath liquid parameters (including type and concentration of volatile buffers, type and content of organic modifiers, use of dopants and inorganic/organic additives, and sheath liquid flow rate) and APPI-MS spray chamber parameters (capillary voltage, vaporizer temperature, nebulizer pressure) were found to have effects on detection sensitivity as well as the profile of mass spectrum. For example, when ammonium acetate was replaced with acetic acid in the sheath liquid, the MS signal was enhanced as much as 90% and the formation of ammonia adduct was effectively suppressed. Next, the separation of MBAP isomers was conducted on internal tapered columns packed with polymeric C18 stationary phase. With the use of a mobile phase consisting of slightly higher acetonitrile content (90%,v/v) and a small amount of tropylium ion, the analysis times were significantly shortened by 20 min without compromising the resolutions between the isomers. Finally, quantitative aspects of the CEC-APPI-MS method were demonstrated using 7-MBAP as the internal standard. The calibration curves of three of the most carcinogenic isomers, namely, 1-MBAP, 3-MBAP, and 11-MBAP, showed good linearity in the range of 2.5-50 microg/mL with a limit of detection at 400 ng/mL.

Supramolecular systems-based extraction-separation techniques coupled to mass spectrometry

The combination of supramolecular chemistry and MS has not only been fruitful in the field of gas-phase fundamental studies of host-guest complexes and supramolecular assemblies. Mass spectrometric analysis has also benefited from the ability of supramolecular systems to behave as pseudophases in which solutes partition from the bulk solvent phase. Supramolecular systems-based extraction and concentration schemes and separation techniques have been widely used in different fields of analytical chemistry and are ideally suited for coupling with MS. This review describes the present status of the application of supramolecular chemistry in mass spectrometric analysis and includes topics such as the use of coacervative liquid-liquid extraction and hemimicelle/admicelle-based SPE of organic compounds prior to chromatography and electrophoresis. It also discusses the recent advances in enantioselective analysis using CD in electrophoresis- and chromatography-MS. The potential and analytical challenges of these approaches in environmental and bioanalytical chemistry, where one can expect significant developments in the future, are outlined.

Recent advances in capillary electrophoresis and capillary electrochromatography of pollutants

Recent advances in the CE and CEC separation, detection, and sample preparation methodologies applied to the determination of a variety of compounds having current or potential environmental relevance have been overviewed. The reviewed literature has illustrated the wide range of CE applications, indicating the continuing interest in CE and CEC in the environmental field.

Recent applications in capillary electrochromatography

In this review research papers on the application of CEC are summarized that have been published between May 2003 and May 2005. First, a short overview is given of trends and developments in CEC that may increase the applicability of the separation technique. Next, application-oriented research using CEC is described in biochemical studies, including proteomics and genomics, in the analysis of food and natural products, and in pharmaceutical, industrial, and environmental analysis.

Recent developments in capillary electrophoresis and capillary electrochromatography of peptides

The article gives a comprehensive review on the recent developments in the applications of high-performance capillary electromigration methods, zone electrophoresis, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography, and electrochromatography, to analysis, preparation, and physicochemical characterization of peptides. The article presents new approaches to the theoretical description and experimental verification of electromigration behavior of peptides, covers the methodological aspects of capillary electroseparations of peptides, such as rational selection of separation conditions, sample preparation, suppression of peptide adsorption, new developments in individual separation modes, and new designs of detection systems. Several types of applications of capillary electromigration methods to peptide analysis are presented: conventional qualitative and quantitative analysis, purity control, determination in biomatrices, monitoring of chemical and enzymatical reactions and physical changes, amino acid and sequence analysis, and peptide mapping of proteins. Some examples of micropreparative peptide separations are given and capabilities of capillary electromigration techniques to provide important physicochemical characteristics of peptides are demonstrated.

Fabrication of Internally Tapered Capillaries for Capillary Electrochromatography Electrospray Ionization Mass Spectrometry

In this study, we report a novel procedure for fabricating internally tapered capillary columns suitable for the coupling of capillary electrochromatography (CEC) to electrospray mass spectrometry (ESI-MS). The internal tapers were prepared by slowly heating the capillary end in a methane/O2 flame. Due to continuous self-shrinking of the inner channel of the capillary, the inside diameter of the opening was reduced to 7-10 microm. The procedure is easy to handle, with no requirement for expensive equipment as well as elimination of problematic grinding of the tip. Several advantages of these new internal tapers, as compared to using externally tapered columns, are described. First, the problems of poor durability and tip breakage associated with external tapering were successfully overcome with the internal taper. A comparison of the online CEC/ESI-MS between external versus internal tapers showed that the latter provides enhanced electrospray stability, resulting in significantly lower short-term noise and very short-term noise values. In turn, the more rugged design of internal tapers allows performing CEC/MS utilizing a harsh polar organic mobile phase, which was not previously successful using an external taper due to higher operating current and electrospray arcing. Next, data on the reproducibility of the internally tapered CEC/MS column using warfarin and beta-blockers as model analytes are presented. For example, when comparing the reproducibility for separation of warfarin under reversed-phase conditions, the internal taper demonstrated superior intraday % RSD (1.6-3.4) as compared to the external taper intraday % RSD (5-6). Last, the applicability of performing quantitative CEC/MS with internally tapered capillaries is demonstrated for simultaneous enantioseparation of beta-blockers. Impressive quantitative results include good linearity of calibration curves (e.g., R2 = 0.9940-0.9988) and limit of detection as low as 30 nM. The sensitive detection of a minor impurity of one enantiomer at the 0.1% level in a major chiral entity buttresses the suitability of compliance with FDA guidelines.

Determination of aerobic-anaerobic metabolism-related compounds in a Chaoborus flavicans population by infusion ion trap mass spectrometry of extracts of individual larvae

In a daily migration, the aquatic larvae of Chaoborus flavicans (a phantom midge) alternate oxygen-saturated and anoxic lake strata. To investigate this cycle, larvae were collected at a natural environment, and acetate, propionate, pyruvate, lactate, glycerol, phosphate, maleate, succinate, glucose and citrate were determined. Each larva was homogenized with 200 microL water and deproteinized with a spin-filter; 50 microL aliquots were mixed with 50 microL of a buffer containing 80 mM propylamine, 20 mM HCl and 0.06 mM 2,4-dihydroxybenzoic acid (internal standard) in methanol. The extracts were infused in an electrospray ionization ion-trap mass spectrometer. The limits of detection for the [M-H](-) peaks ranged from 2 microM for pyruvate and lactate to 200 microM for acetate and glycerol. The MS(2) ion-trap spectra obtained at pH 7 (ammonium acetate buffer) were used to distinguish maleate (cis-2-butenedioic), which gave [M-CO(2)-H](-) (m/z 71), from fumarate (trans-2-butenedioic), which showed first a loss of water yielding an instable peak at m/z 97. The compounds involved in the aerobic-anaerobic adjustment of the metabolism were revealed by linear discriminant analysis. Acetate, citrate, glucose, maleate (which decreased during the daytime), and particularly succinate (which increased), showed the maximal discrimination power between the day- and night-time samples.

Liquid chromatography-electrospray ionization-mass spectrometry: the future of DNA adduct detection

Over the past 40 years considerable emphasis has been placed on the development of accurate and sensitive methods for the detection and quantitation of DNA adducts. The formation of DNA adducts resulting from the covalent interaction of genotoxic carcinogens with DNA, derived from exogenous and endogenous sources, either directly or following metabolic activation, can if not repaired lead to mutations in critical genes such as those involved in the regulation of cellular growth and subsequent development of cancer. The major analytical challenge has been to detect levels of DNA adducts at the level of 0.1-1 adducts per 10(8) unmodified DNA bases using only low microgram amounts of DNA, and with high specificity and accuracy, in humans exposed to genotoxic carcinogens derived from occupational, environmental, dietary and life-style sources. In this review we will highlight the merits as well as discuss the progress made by liquid chromatography coupled to electrospray ionization mass spectrometry as a method for DNA adduct detection.

Quantitation in capillary electrophoresis-mass spectrometry

CE-MS has evolved into a strong alternative to LC-MS. Most of CE-MS applications deal with characterization and identification. However, quantitative aspects have gained importance in, e.g., pharmaceutical and biotechnological applications. Here we summarize and evaluate various methodological aspects in order to achieve sensitive and reproducible results. Similar to LC-MS, aspects of matrix influence on the electrospray process need to be carefully addressed when quantitative results are intended by CE-MS. Due to a more complicated coupling special emphasis needs to be put on the CE-MS interface. Generally linearity over more than three orders of magnitude can be achieved by CE-ESI-MS. Furthermore, a literature survey has been performed in order to give an overview over quantitative measurements performed by CE-MS. The precision can be doubled when changing from a structural related to an isotopically labeled internal standard. Thus a level of precision better than 5% RSD can be achieved.

A silica-based monolithic column in capillary HPLC and CEC coupled with ESI-MS or electrospray-atmospheric-pressure laser ionization-MS

We describe the successful coupling of CEC and capillary HPLC with the recently developed atmospheric-pressure laser ionization (APLI) method. APLI is suitable for selectively and sensitively ionizing nonpolar aromatic compounds at ambient pressure for subsequent mass-selective detection. The polycyclic aromatic hydrocarbons used as analytes are first separated either by CEC on a silica-based monolithic column or by capillary HPLC. The eluent, along with a sheath flow, is volatilized by microelectrospray and then selectively ionized by excimer laser (KrF*) radiation via two-photon excitation. A QTOF-MS is used as mass-selective detector. This interface combination makes soft ionization of thermally labile nonpolar aromatic analytes possible.

Advances in the analysis of proteins and peptides by capillary electrophoresis with matrix-assisted laser desorption/ionization and electrospray-mass spectrometry detection

High throughput, outstanding certainty in peptide/protein identification, exceptional resolution, and quantitative information are essential pillars in proteome research. Capillary electrophoresis (CE) coupled to mass spectrometry (MS) has proven to meet these requirements. Soft ionization techniques, such as matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI), have paved the way for the story of success of CE-MS in the analysis of biomolecules and both approaches are subject of discussion in this article. Meanwhile, CE-MS is far away from representing a homogeneous field. Therefore the review will cover a vast area including the coupling of different modes of CE (capillary zone electrophoresis, capillary isoelectric foscusing, capillary electrochromatography, micellar electrokinetic chromatography, nonaqueous capillary electrophoresis) to MS as well as on-line preconcentration techniques (transient capillary isotachophoresis, solid-phase extraction, membrane preconcentration) applied to compensate for restricted detection sensitivity. Special attention is given to improvements in interfacing, namely addressing nanospray and coaxial sheath liquid design. Peptide mapping, collision-induced dissociation with subsequent tandem MS, and amendments in mass accuracy of instruments improve information validity gained from MS data. With 2-D on-line coupling of liquid chromatography (LC) and CE a further topic will be discussed. A special section is dedicated to recent attempts in establishing CE-ESI-MS in proteomics, in the clinical and diagnostic field, and in the food sector.

Capillary Electrochromatography−Mass Spectrometry of Zwitterionic Surfactants

This work describes the on-line hyphenation of a packed capillary electrochromatography (CEC) column with an internally tapered tip coupled to electrospray ionization-mass spectrometry (ESI-MS) and atmospheric pressure chemical ionization-mass spectrometry (APCI-MS) for the analysis of betaine-type amphoteric or zwitterionic surfactants (Zwittergent). A systematic investigation of the CEC separation and MS detection parameters comparing ESI and APCI is shown. First, a detailed and optimized manufacturing procedure for fabrication of the CEC-MS column with a reproducible internally tapered tip (7-9 microm) is presented. Next, the optimization of the separation parameters by varying the C(18) stationary-phase particle size (3 versus 1.5 microm), as well as mobile-phase composition including acetonitrile (ACN) volume fraction, ionic strength, and pH is described. The optimized separation is achieved using 3-microm C(18) packing with 75% ACN (v/v), 5 mM Tris at pH 8.0. Optimization for on-line CEC-ESI-MS detection is then done varying both the sheath liquid and spray chamber parameters while evaluating the use of random versus structured factorial table experimental designs. The more structured approach allows fundamental analysis of individual ESI-MS parameters while minimizing CEC and MS equilibration time between settings. A comparison of CEC-ESI-MS to CEC-APCI-MS using similar sheath and spray chamber conditions presents new insight for coupling of CEC to APCI-MS. The sheath liquid flow rate required to maintain adequate sensitivity is much higher in APCI source (50 microL/min) as compared to the ESI source (3 microL/min). The on-line mass spectra obtained in the full scan mode show that fragmentation in the two sources occurs at different positions on the Zwittergent molecules. For ESI-MS, the protonated molecular ion is always highest in abundance with minor fragmentation occurring due to the loss of the alkyl chain. In contrast, the APCI-MS spectra show that the highest abundant ion resulted by elimination of propane sulfonate from the Zwittergent molecule. A comparison of the sensitivity between the two sources in positive ionization SIM mode shows that CEC-ESI-MS provides an impressive limit of detection (LOD) of 5 ng/mL, which is at least 3 orders of magnitude lower than CEC-APCI-MS (LOD 100 microg/mL). Finally, the optimized CEC-MS methods comparing ESI and APCI are applied for separation and structural characterization of a real industrial zwittergent sample, Rewoteric AM CAS.

Determination of organic contaminants in food by capillary electrophoresis

This review addresses recent advances in the analysis of organic contaminants, such as antibiotics, pesticides, biological toxins, and food-borne pathogens, in foods by capillary electrophoresis (CE). Special attention is paid to those aspects that increase sensitivity and/or selectivity, such as sample extraction and concentration, on-line preconcentration techniques (stacking), affinity capillaries or/and specific detectors (laser induced fluorescence (LIF), mass spectrometry (MS)). The various CE modes used to separate the compounds and the quantification strategies are also examined. As a result, this work presents an updated overview on the principal applications of CE, together with a discussion of their main advantages and drawbacks, and an outline of future trends in the analysis of organic contaminants in food.

Capillary electrophoresis-mass spectrometry: recent advances to the analysis of small achiral and chiral solutes

We describe here the state-of-the-art development of on-line capillary electrophoresis-mass spectrometry (CE-MS) over the last two years. Technological developments included are novel designs of new interfaces and ionization sources, new capillary coatings, buffers, and micelles as well as application of various modes of CE-MS published in the recent literature. The areas of CE-MS application in analysis of small achiral and chiral solutes are covered in sections that highlight the recent advances and possibilities of each mode of CE-MS. Application areas reviewed in this paper include achiral and chiral pharmaceuticals, agrochemicals, carbohydrates, and small peptides. The separation of enantiomers using micellar electrokinetic chromatography (MEKC)-MS with molecular micelles and capillary electrochromatography (CEC)-MS using pack tapered columns appears to provide good tolerance to electrospray stability for routine on-line CE-MS. These two modes seem to be very suitable for sensitive detection of chiral pharmaceuticals in biological samples, but their use will probably increase in the near future. Overall, it seems that one mode of CE-MS, in particular capillary zone electrophoresis (CZE)-MS, is now recognized as established technique for analysis of small charged solutes, but other modes, such as MEKC-MS and CEC-MS, are still within a period of development in terms of both MS-compatible pseudostationary phases and columns as well as applications.

Combining capillary electrophoresis with mass spectrometry for applications in proteomics

Mass spectrometry (MS)-based proteomics is currently dominated by the analysis of peptides originating either from digestion of proteins separated by two-dimensional gel electrophoresis (2-DE) or from global digestion; the simple peptide mixtures obtained from digestion of gel-separated proteins do not usually require further separation, while the complex peptide mixtures obtained by global digestion are most frequently separated by chromatographic techniques. Capillary electrophoresis (CE) provides alternatives to 2-DE for protein separation and alternatives to chromatography for peptide separation. This review attempts to elucidate how the most promising CE modes, capillary zone electrophoresis (CZE) and capillary isoelectric focusing (CIEF), might best be applied to MS-based proteomics. CE-MS interfacing, mass analyzer performance, column coating to minimize analyte adsorption, and sample stacking for CZE are considered prior to examining numerous applications. Finally, multidimensional systems that incorporate CE techniques are examined; CZE often finds use as a fast, final dimension before ionization for MS, while CIEF, being an equilibrium technique, is well-suited to being the first dimension in automated fractionation systems.

A soft on-column metal coating procedure for robust sheathless electrospray emitters used in capillary electrophoresis-mass spectrometry

An on-column metal coating procedure was developed for sheathless electrospray emitters, based on Justus von Liebig's electroless silver mirror reaction followed by electrochemical deposition of gold onto the silver layer. The coating procedure is straightforward, mild, inexpensive, and can be performed with standard laboratory equipment. A long-term (600 h) stability investigation of the conductive coating was carried out by continuous electrospray in the positive electrospray mode, and no degradation in performance was found. The simplicity of the coating procedure and the robustness of the spray tips makes the spray tips highly suitable to couple delicate wall-coated or monolithic capillary columns to mass spectrometry. Peptide mixtures were separated by capillary electrophoresis and injected into either a Hadamard-transform time-of-flight mass analyzer or a commercial quadrupole mass analyzer using the described sheathless electrospray emitters. The performance was judged to be excellent.