Capillary electrophoresis-atmospheric pressure chemical ionization-mass spectrometry using an orthogonal interface: set-up and system parameters

Development of transient trapping micellar electrokinetic chromatography coupled with mass spectrometry for steroids analysis

An on-line sample preconcentration technique based on transient trapping (tr-trapping) in micellar electrokinetic chromatography (MEKC) was applied for steroid detection with UV (tr-trapping-UV) and electrospray ionization mass spectrometry detection (tr-trapping-ESI-MS). ESI-MS was used to improve the sensitivity in MEKC. The MEKC separation was carried out using volatile ammonium formate as a background solution to facilitate the coupling with ESI-MS. The partial introduction of a sodium dodecyl sulfate (SDS) micellar solution before the introduction of a sample solution to the capillary provided the effective preconcentration of analytes. At the same time, the SDS micelle would not enter the ESI-MS system, so its interference in ESI-MS detection was suppressed under the optimal condition, then five steroids can be separated by the developed method. In tr-trapping-ESI-MS, an acidic condition of pH 3.5 was employed to suppress the electroosmotic flow, which can avoid micellar solution migrating to the MS instrument. The developed method showed that the micellar solution requires a twofold slower time than the sample to migrate along the column, which can prohibit the cause of the problem with the MS instrument and interference signal of SDS in the steroid's detection. The tr-trapping-ESI-MS protocol showed up to 540-fold enhancements of the peak intensity and 50-fold improvement of the limit of detection compared with capillary zone electrophoresis using androsterone as a model sample.

Recent applications of metabolomics in plant breeding

Metabolites play a central role in maintaining organismal life and in defining crop phenotypes, such as nutritional value, fragrance, color, and stress resistance. Among the 'omes' in biology, the metabolome is the closest to the phenotype. Consequently, metabolomics has been applied to crop improvement as method for monitoring changes in chemical compositions, clarifying the mechanisms underlying cellular functions, discovering markers and diagnostics, and phenotyping for mQTL, mGWAS, and metabolite-genome predictions. In this review, 359 reports of the most recent applications of metabolomics to plant breeding-related studies were examined. In addition to the major crops, more than 160 other crops including rare medicinal plants were considered. One bottleneck associated with using metabolomics is the wide array of instruments that are used to obtain data and the ambiguity associated with metabolite identification and quantification. To further the application of metabolomics to plant breeding, the features and perspectives of the technology are discussed.

Establishing repeatability and ruggedness of chiral separations in micellar electrokinetic chromatography mass spectrometry: Combined use of covalently bonded capillary column and molecular micelles

Although micellar electrokinetic chromatography-mass spectrometry (MEKC-MS) using bare silica capillary filled with molecular micelles is an advantageous hyphenated technique for chiral analysis, it is still in the developmental stage. This is mainly because of the lower repeatability of retention time and peak area associated with the difficulty in controlling electroosmotic flow on bare silica capillaries. Besides the lower robustness and electrospray erosion of the fused-silica capillary tip, the lifetime is limited for 10-15 runs per capillary column. We have tested a new MEKC-MS method to eradicate this problem using a covalently bonded 2-acrylamido-2-methyl-1-propane-sulfonic acid (AMPS) column filled with free floating molecular micelles, polysodium N-undecenoxy carbonyl-L-leucinate (poly-L-SUCL). Simultaneous enantiomeric separations and MS/MS detection of three β-blockers [atenolol (ATEN), metoprolol (METO) and, pindolol (PINDO)] was achieved within 25 min with improved column lifetime of at least 45-50 runs. Excellent repeatability of retention time was observed for β-blockers, as evidenced by the relative standard deviation of less than 2% and 3% for intra-capillary and inter-capillary column, respectively. The linear calibration range of both β-blockers was simultaneously established using enantiomers of PINDO as an internal standard. The limit of detection and the lower limit of quantitation were 0.2 μg/mL and 0.5 μg/mL, respectively, for both ATEN and METO. Acceptable recovery of the enantiomeric content of the commercial METO tablet (98-99.5%) and ATEN tablet (89-92.5%) were obtained with adequate system suitability for the precision of peak area (≤10% RSD) under optimum conditions. The developed MEKC-MS approach was extended, which provided broader repeatibility of chiral separation to a panel of primary, secondary and tertiary amines as well as one anionic chiral compound.

Application of Atmospheric Pressure Photoionization H/D-exchange Mass Spectrometry for Speciation of Sulfur-containing Compounds

Herein we report the observation of atmospheric pressure in-source hydrogen-deuterium exchange (HDX) of thiol group for the first time. The HDX for thiol group was optimized for positive atmospheric pressure photoionization (APPI) mass spectrometry (MS). The optimized HDX-MS was applied for 31 model compounds (thiols, thiophenes, and sulfides) to demonstrate that exchanged peaks were observed only for thiols. The optimized method has been successfully applied to the isolated fractions of sulfur-rich oil samples. The exchange of one and two thiol hydrogens with deuterium was observed in the thiol fraction; no HDX was observed in the other fractions. Thus, the results presented in this study demonstrate that the HDX-MS method using APPI ionization source can be effective for speciation of sulfur compounds. This method has the potential to be used to access corrosion problems caused by thiol-containing compounds. Graphical Abstract ᅟ.

Enantioselective capillary electrophoresis-mass spectrometry of amino acids in cerebrospinal fluid using a chiral derivatizing agent and volatile surfactant

The sensitivity of coupled enantioselective capillary electrophoresis-mass spectrometry (CE-MS) of amino acids (AAs) is often hampered by the chiral selectors in the background electrolyte (BGE). A new method is presented in which the use of a chiral selector is circumvented by employing (+)-1-(9-fluorenyl)ethyl chloroformate (FLEC) as chiral AA derivatizing agent and ammonium perfluorooctanoate (APFO) as a volatile pseudostationary phase for separation of the formed diastereomers. Efficient AA derivatization with FLEC was completed within 10 min. Infusion experiments showed that the APFO concentration hardly affects the MS response of FLEC-AAs and presents significantly less ion suppression than equal concentrations of ammonium acetate. The effect of the pH and APFO concentration of the BGE and the capillary temperature were studied in order to achieve optimized enantioseparation. Optimization of CE-MS parameters, such as sheath-liquid composition and flow rate, ESI and MS settings was performed in order to prevent analyte fragmentation and achieve sensitive detection. Selective detection and quantification of 14 chiral proteinogenic AAs was achieved with chiral resolution between 1.2 and 8.6, and limits of detection ranging from 130 to 630 nM injected concentration. Aspartic acid and glutamic acid were detected, but not enantioseparated. The optimized method was applied to the analysis of chiral AAs in cerebrospinal fluid (CSF). Good linearity (R(2) > 0.99) and acceptable peak area and electrophoretic mobility repeatability (RSDs below 21% and 2.4%, respectively) were achieved for the chiral proteinogenic AAs, with sensitivity and chiral resolution mostly similar to obtained for standard solutions. Next to l-AAs, endogenous levels of d-serine and d-glutamine could be measured in CSF revealing enantiomeric ratios of 4.8%-8.0% and 0.34%-0.74%, respectively, and indicating the method's potential for the analysis of low concentrations of d-AAs in presence of abundant l-AAs.

Mass spectrometry and NMR spectroscopy: modern high-end detectors for high resolution separation techniques--state of the art in natural product HPLC-MS, HPLC-NMR, and CE-MS hyphenations

Current natural product research is unthinkable without the use of high resolution separation techniques as high performance liquid chromatography or capillary electrophoresis (HPLC or CE respectively) combined with mass spectrometers (MS) or nuclear magnetic resonance (NMR) spectrometers. These hyphenated instrumental analysis platforms (CE-MS, HPLC-MS or HPLC-NMR) are valuable tools for natural product de novo identification, as well as the authentication, distribution, and quantification of constituents in biogenic raw materials, natural medicines and biological materials obtained from model organisms, animals and humans. Moreover, metabolic profiling and metabolic fingerprinting applications can be addressed as well as pharmacodynamic and pharmacokinetic issues. This review provides an overview of latest technological developments, discusses the assets and drawbacks of the available hyphenation techniques, and describes typical analytical workflows.

Ionization techniques in capillary electrophoresis-mass spectrometry: principles, design, and application

A major step forward in the development and application of capillary electrophoresis (CE) was its coupling to ESI-MS, first reported in 1987. More than two decades later, ESI has remained the principal ionization technique in CE-MS, but a number of other ionization techniques have also been implemented. In this review the state-of-the-art in the employment of soft ionization techniques for CE-MS is presented. First the fundamentals and general challenges of hyphenating conventional CE and microchip electrophoresis with MS are outlined. After elaborating on the characteristics and role of ESI, emphasis is put on alternative ionization techniques including sonic spray ionization (SSI), thermospray ionization (TSI), atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI), matrix-assisted laser desorption ionization (MALDI) and continuous-flow fast atom bombardment (CF-FAB). The principle of each ionization technique is outlined and the experimental set-ups of the CE-MS couplings are described. The strengths and limitations of each ionization technique with respect to CE-MS are discussed and the applicability of the various systems is illustrated by a number of typical examples.

New trends in quantification of acrylamide in food products

Methods applied in acrylamide quantification in foods have been reviewed in this paper. Novel analytical techniques like capillary electrophoresis (CE), immunoenzymatic test (ELISA) and electrochemical biosensors, which can replace traditional methods like high performance liquid chromatography (HPLC) and gas chromatography (GC) were presented. Short time of analysis and high resolution power of electrophoretic techniques caused that they became routinely used in food analysis apart from high performance liquid chromatography and gas chromatography. Application of modern chromatography methods like ultra performance liquid chromatography (UPLC) in acrylamide quantification considerably shortened the time of analysis and decreased the consumption of indispensable reagents. The most promising approaches to acrylamide quantification in foods are electrochemical biosensors and immunoenzymatic tests. In contrast to chromatography and electrophoretic methods they require neither expensive equipment nor time consuming sample preparation and allow for fast screening of numerous samples without the usage of sophisticated apparatuses. Because of many advantages such as miniaturization, rapid and simple analysis, and high sensitivity and selectivity, biosensors are thought to replace conventional methods of acrylamide quantification in food.

Recent advances in CE-MS: Synergy of wet chemistry and instrumentation innovations

CE with MS detection is a hyphenated technique which greatly improves the ability of CE to deal with real samples, especially with those coming from biology and medicine, where the target analytes are present as trace amounts in very complex matrices. CE-MS is now almost a routine technique performed on commercially available instruments. It faces currently a tremendous development of the technique itself as well as of its wide application area. Great interest in CE-MS is reflected in the scientific literature by many original research articles and also by numerous reviews. The review presented here has a general scope and belongs to a series of regularly published reviews on the topic. It covers the literature from the last 2 years, since January 2008 till June 2010. It brings a critical selection of related literature sorted into groups reflecting the main topics of actual scientific interest: (i) innovations in CE-ESI-MS, (ii) use of alternative interfaces, and (iii) ways to enhance sensitivity. Special attention is paid to novel electrolyte systems amenable to CE-MS including nonvolatile BGEs, to advanced CE separation principles such as MEKC, MEEKC, chiral CE, and to the use of preconcentration techniques.

Recent developments in instrumentation for capillary electrophoresis and microchip-capillary electrophoresis

Over the last years, there has been an explosion in the number of developments and applications of CE and microchip-CE. In part, this growth has been the direct consequence of recent developments in instrumentation associated with CE. This review, which is focused on the contributions published in the last 5 years, is intended to complement the articles presented in this special issue dedicated to instrumentation and to provide an overview of the general trends and some of the most remarkable developments published in the areas of high-voltage power supplies, detectors, auxiliary components, and compact systems. It also includes a few examples of alternative uses of and modifications to traditional CE instruments.

Drug impurity profiling by capillary electrophoresis/mass spectrometry using various ionization techniques

Capillary electrophoresis/mass spectrometry (CE/MS) is predominantly carried out using electrospray ionization (ESI). Recently, atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) have become available for CE/MS. With the VUV lamp turned off, the APPI source may also be used for CE/MS by thermospray ionization (TSI). In the present study the suitability of ESI, APCI, APPI and TSI for drug impurity profiling by CE/MS in the positive ion mode is evaluated. The drugs carbachol, lidocaine and proguanil and their potential impurities were used as test compounds, representing different molecular polarities. A background electrolyte of 100 mM acetic acid (pH 4.5) provided baseline separation of nearly all impurities from the respective drugs. APPI yielded both even- and odd-electron ions, whereas the other ionization techniques produced even-electron ions only. In-source fragmentation was more pronounced with APCI and APPI than with ESI and TSI, which was most obvious for proguanil and its impurities. In general, ESI and TSI appeared the most efficient ionization techniques for impurities that are charged in solution achieving detection limits of 100 ng/mL (full-scan mode). APPI and APCI showed a lower efficiency, but allowed ionization of low and high polarity analytes, although quaternary ammonium compounds (e.g. carbachol) could not be detected. Largely neutral compounds, such as the lidocaine impurity 2,6-dimethylaniline, could not be detected by TSI, and yielded similar detection limits (500 ng/mL) for ESI, APPI and APCI. In many cases, impurity detection at the 0.1% (w/w) level was possible when 1 mg/mL of parent drug was injected with at least one of the CE/MS systems. Overall, the tested CE/MS systems provide complementary information as illustrated by the detection and identification of an unknown impurity in carbachol.