The efficiency of desorption/ionization becomes more critical as the sampled surface area decreases. Desorption electrospray and desorption nanoelectrospray belong to ambient ionizations and enable direct surface analysis including mass spectrometric imaging. Lateral resolution in tens of micrometers was demonstrated for desorption nanoelectrospray previously, but sensitivity of the surface scan can be an issue. For desorption electrospray, the drag force in the source is driven by the flow of used gases and vacuum suction. Ion signal intensity can be improved by controlling the nebulizing gas flow rate or auxiliary pumping of a closed compartment in front of the mass spectrometer inlet. Because nanoelectrospray generates charged droplets without the assistance of a nebulizing gas, only vacuum suction drives the gas flow. In this study, the effect of pressure drop between the atmospheric and evacuated region of a mass spectrometer on the ion signal intensity was investigated for desorption nanoelectrospray. A modification of the commercial inlet was designed. An auxiliary pump was directly connected to an inner compartment of the modified mass spectrometer inlet through a needle valve that enabled the regulation of the reduced pressure. Adjustment of the pressure drop significantly increased signal intensity (more than one order of magnitude in some cases). To a lesser extent, the temperature of a heated capillary (an integral part of the inlet) also influenced the signal intensity. The applicability of desorption nanoelectrospray equipped with pressure regulation was demonstrated by the analysis of synthetic cathinones or a pill of paracetamol. Because pressure in the inlet depends on the diameters of orifices and the power of vacuum systems of mass spectrometers, the effect of the pressure regulation can be different for different instruments. Nevertheless, the presented results confirmed the importance of pressure drop-driven transport for desorption nanoelectrospray efficiency and can encourage its new applications.
- Klíčová slova
- cathinones, desorption nanoelectrospray, mass spectrometry, new psychoactive substances, pressure drop regulation,
- Publikační typ
- časopisecké články MeSH
Cysteine protease from grapevine (Vitis vinifera) belongs to those resistant proteins, which survive the process of vinification and can therefore be detected as wine components. Its amino acid sequence shows a homology to other members of the papain family, but the enzyme has only partially been explored so far. In order to get more biochemical information with the help of mass spectrometry (MS), wine proteins were collected by ultrafiltration and separated by gel permeation chromatography. The purified enzyme surprisingly displayed a high molecular mass value of around 200 kDa, indicating a possible oligomeric status and aggregation, as it entered only negligibly the separating 10% gel during polyacrylamide gel electrophoresis. The isoelectric point (pI) value of 3.6 was determined by chromatofocusing. Matrix-assisted laser desorption/ionization (MALDI)-MS was employed to evaluate the cleavage specificity and usefulness of the isolated cysteine protease in protein and peptide research. A potential applicability could be anticipated from the efficient digestion performance in volatile ammonium formate buffers at pH 3. Common peptides were digested and the resulting products analyzed by MS/MS sequencing. Then, mixtures of protein standards and extracted barley nuclear proteins were processed in the same way. Grape cysteine protease is nonspecific but shows a certain preference for Arg, Lys, and also Leu residues. Compared with papain, it seems not to require fully the presence of a large hydrophobic residue adjacent to that at the cleavage site. The enzyme is suitable for protein research as it produces peptides of a reasonable length in acidic pH.
- Klíčová slova
- RD21, cysteine protease, digestion, liquid chromatography, papain, peptide,
- MeSH
- cysteinové proteasy chemie izolace a purifikace metabolismus MeSH
- koncentrace vodíkových iontů MeSH
- ovoce enzymologie MeSH
- peptidy analýza metabolismus MeSH
- proteiny analýza metabolismus MeSH
- spektrometrie hmotnostní - ionizace laserem za účasti matrice metody MeSH
- substrátová specifita MeSH
- tandemová hmotnostní spektrometrie MeSH
- víno analýza MeSH
- Vitis enzymologie MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- cysteinové proteasy MeSH
- peptidy MeSH
- proteiny MeSH
The potential use of ethanol as an internal standard (IS) for GC-MS analysis was studied. The paper describes the analysis of spirit drinks and other alcoholic products which consist of a mixture of water, ethanol, and volatile compounds. In the suggested method, ethanol was employed as an IS for the common procedure of volatile compounds quantification. A number of standard solutions of nine compounds with different concentrations was prepared in a water-ethanol matrix and measured with GC-MS in the SIM mode. Two possible approaches were suggested to avoid detector saturation during ethanol detection. The first one consisted in using less abundant m/z 47 as quantifiers. These ions mainly correspond to unfragmented heavy ethanol molecules containing one 13 C isotope. The second method consisted in reduction of the voltage of MS electron multiplier. The experiment also included the preparation and subsequent dilution of the standard solution and ethanol with water, which determined the linearity of the modified MS response relative to the ethanol content. Analysis of the obtained results revealed that volatile compounds can be successfully accurately determined with GC-MS by employing ethanol as an IS. Application of the suggested method is not limited to the reported volatile compounds and alcoholic products.
- Klíčová slova
- GC-MS, alcoholic products, ethanol, internal standard, quantification, volatile compounds,
- Publikační typ
- časopisecké články MeSH
Within the growing community of Fourier transform mass spectrometry users, the identification of fine isotope structure has become an indispensable method for molecular formula determination. In this work, the fine isotope envelopes for accessing the mutual ratio of 2 closely related pyoverdines in a mixture were used. Bacterial siderophores pyoverdines D and E cannot be easily separated via liquid chromatography-mass spectrometry because their structures differ in (de)amidation at the respective chromophore parts only. Their mutual ratio was determined in a mixture via nuclear magnetic resonance spectroscopy and semiquantitative mass spectrometry using our open-source software CycloBranch, which represents a genuine free tool supporting the determination of fine isotope structures in both conventional and product ion mass spectra. Native Bruker, Thermo, and Waters data formats are supported in addition to XML and plain text formats.
- Klíčová slova
- CycloBranch, NMR, fine isotope structure, mass spectrum, pyoverdine, quantitation,
- Publikační typ
- časopisecké články MeSH
Macromolecular polyelectrolytes are gaining considerable attention for the application in medicine that implies their detailed characterization. We have successfully applied electrospray ionization mass spectrometry (ESI MS) to the analysis of defects in the structure of three generations of polycationic carbosilane dendrimers bearing series of quarternary phosphonium groups at their periphery. Besides expected defects caused by incomplete conversion of particular reaction steps during the synthesis of dendritic scaffold and subsequent peripheral functionalization, also, several products of side reactions were observed together with defects created in the course of measurement (particularly ion exchange products). Defective molecules can be to some extent separated by means of gel permeation chromatography that proves that they are not products of in source fragmentation processes. Within the reaction sequence used for the synthesis of dendrimers under study, hydrosilylation was the source of most defects; the effectivity of quarternization depends on the type of phosphine. Results confirm high sensitivity of ESI MS towards defects, stability of the carbosilane skeleton towards fragmentation under the conditions of ESI ionization, and capability to detect both lower- and higher-molecular weight impurities arising from the synthetic sequence in the same m/z range as the target dendrimer, thus providing valuable view of the polydispersity.
- Klíčová slova
- ESI mass spectrometry, carbosilane dendrimers, defect analysis, phosphonium, polycationic,
- Publikační typ
- časopisecké články MeSH
We report non-chiral amino acid residues cis- and trans-1,4-diaminocyclohexane-1-carboxylic acid (cyclo-ornithine, cO) that exhibit unprecedented stereospecific control of backbone dissociations of singly charged peptide cations and hydrogen-rich cation radicals produced by electron-transfer dissociation. Upon collision-induced dissociation (CID) in the slow heating regime, peptide cations containing trans-cO residues undergo facile backbone cleavages of amide bonds C-terminal to trans-cO. By contrast, peptides with cis-cO residues undergo dissociations at several amide bonds along the peptide ion backbone. Diastereoisomeric cO-containing peptides thus provide remarkably distinct tandem mass spectra. The stereospecific effect in CID of the trans-cO residue is explained by syn-facially directed proton transfer from the 4-ammonium group at cO to the C-terminal amide followed by neighboring group participation in the cleavage of the CO-NH bond, analogous to the aspartic acid and ornithine effects. Backbone dissociations of diastereoisomeric cO-containing peptide ions generate distinct [bn ]+ -type fragment ions that were characterized by CID-MS3 spectra. Stereospecific control is also reported for electron-transfer dissociation of cis- and trans-cO containing doubly charged peptide ions. The stereospecific effect upon electron transfer is related to the different conformations of doubly charged peptide ions that affect the electron attachment sites and ensuing N-Cα bond dissociations.
- Klíčová slova
- cis and trans isomers, cyclo ornithine, peptide dissociations, peptide ion structures, stereochemistry,
- MeSH
- aminokyseliny chemie MeSH
- cyklohexylaminy chemie MeSH
- elektrony MeSH
- molekulární modely MeSH
- ornithin analogy a deriváty chemie MeSH
- peptidy chemie MeSH
- sekvence aminokyselin MeSH
- stereoizomerie MeSH
- tandemová hmotnostní spektrometrie MeSH
- vodík MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- 1,4-diaminocyclohexane MeSH Prohlížeč
- aminokyseliny MeSH
- cyklohexylaminy MeSH
- ornithin MeSH
- peptidy MeSH
- vodík MeSH
The paper focuses on the optimization, settings and validation of direct analysis in real time coupled with time-of-flight detector when used for the evaluation of the quality of selected herbal teas (fennel, chamomile, nettle, linden, peppermint, thyme, lemon balm, marigold, sage, rose hip and St. John's wort). The ionization mode, the optimal ionization temperature and the type of solvent for sample extraction were optimized. The characteristic compounds of the analysed herbal teas (glycosides, flavonoids and phenolic and terpenic substances, such as chamazulene, anethole, menthol, thymol, salviol and hypericin) were detected. The obtained mass spectra were evaluated by multidimensional chemometric methods, such as cluster analysis, linear discriminate analysis and principal component analysis. The chemometric methods showed that the single variety herbal teas were grouped according to their taxonomic affiliation. The developed method is suitable for quick identification of herbs and can be potentially used for assessing the quality and authenticity of herbal teas. Direct analysis in real time/time-of-flight-MS is also suitable for the evaluation of selected substances contained in the mentioned herbs and herbal products. Copyright © 2017 John Wiley & Sons, Ltd.
- Klíčová slova
- authenticity, chemometric, herbal tea, herbs, quality, statistical analysis,
- MeSH
- bylinné čaje analýza MeSH
- fenoly analýza MeSH
- flavonoidy analýza MeSH
- glykosidy analýza MeSH
- hmotnostní spektrometrie metody MeSH
- rostlinné extrakty chemie MeSH
- terpeny analýza MeSH
- Publikační typ
- časopisecké články MeSH
- hodnotící studie MeSH
- práce podpořená grantem MeSH
- Názvy látek
- bylinné čaje MeSH
- fenoly MeSH
- flavonoidy MeSH
- glykosidy MeSH
- rostlinné extrakty MeSH
- terpeny MeSH
We report the evaluation of several mass spectrometry-based methods for the determination of carisoprodol and meprobamate in samples obtained from the rat brain by in vivo intracranial microdialyis. Among the techniques that aspire to perform analyses without chromatographic separation and thereby increase throughput, chip-based nanoelectrospray ionization and the use of an atmospheric pressure solids analysis probe fell short of requirements because of insufficient detection sensitivity and hard ionization, respectively. Although direct analysis in real time provided the required soft ionization, shortcomings of a tandem mass spectrometry-based assay also included inadequate detection sensitivity and, in addition, poor quantitative reproducibility. Therefore, liquid chromatography coupled with atmospheric pressure chemical ionization tandem mass spectrometry was developed to determine carisoprodol and meprobamate from artificial cerebrospinal fluid as the medium. No desalting and/or extraction of the samples was necessary. The assay, combined with in vivo sampling via intracranial microdialyis, afforded time-resolved concentration profiles for the drug and its major metabolite from the nucleus accumbens region of the brain in rats after systemic administration of carisoprodol. Copyright © 2016 John Wiley & Sons, Ltd.
- Klíčová slova
- LC-MS/MS, atmospheric pressure chemical ionization, atmospheric pressure solids analysis probe, carisoprodol, direct analysis in real time, in vivo intracranial microdialysis, meprobamate, nanoelectrospray ionization,
- MeSH
- hmotnostní spektrometrie s elektrosprejovou ionizací MeSH
- karisoprodol mozkomíšní mok metabolismus MeSH
- lidé MeSH
- meprobamát mozkomíšní mok metabolismus MeSH
- mikrodialýza MeSH
- mozek metabolismus MeSH
- potkani Sprague-Dawley MeSH
- reprodukovatelnost výsledků MeSH
- tandemová hmotnostní spektrometrie MeSH
- vysokoúčinná kapalinová chromatografie MeSH
- zvířata MeSH
- Check Tag
- lidé MeSH
- mužské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- Názvy látek
- karisoprodol MeSH
- meprobamát MeSH
- Klíčová slova
- adulteration, dietary supplements, phosphodiesterase-5 inhibitors, tandem mass spectrometry, transmission-mode desorption electrospray ionization, ultrahigh performance liquid chromatography,
- MeSH
- cyklické nukleotidfosfodiesterasy, typ 5 * MeSH
- hmotnostní spektrometrie s elektrosprejovou ionizací MeSH
- hmotnostní spektrometrie MeSH
- inhibitory fosfodiesterasy 5 * MeSH
- potravní doplňky MeSH
- vysokoúčinná kapalinová chromatografie MeSH
- Publikační typ
- dopisy MeSH
- komentáře MeSH
- práce podpořená grantem MeSH
- Názvy látek
- cyklické nukleotidfosfodiesterasy, typ 5 * MeSH
- inhibitory fosfodiesterasy 5 * MeSH
DART (Direct Analysis in Real Time) coupled with Time-of-Flight Mass Spectrometry (TOF/MS) has been used for analyses of ice-teas. The article focuses on quality and authenticity of ice-teas as one of the most important tea-based products on the market. Twenty-one samples of ice-teas (black and green) were analysed. Selected compounds of ice-teas were determined: theobromine, caffeine, total phenolic compounds, total soluble solids, total amino acid concentration, preservatives and saccharides were determined. Fingerprints of DART-TOF/MS spectra were used for comprehensive assessment of the ice-tea samples. The DART-TOF/MS method was used for monitoring the following compounds: citric acid, caffeine, saccharides, artificial sweeteners (saccharin, acesulphame K), and preservatives (sorbic and benzoic acid), phosphoric acid and phenolic compounds. The measured data were subjected to a principal components analysis. The HPLC and DART-TOF/MS methods were compared in terms of determination of selected compounds (caffeine, benzoic acid, sorbic acid and saccharides) in the ice-teas. The DART-TOF/MS technique seems to be a suitable method for fast screening, testing quality and authenticity of tea-based products.
- Klíčová slova
- DART, PCA analysis, TOF, ice-tea, quality,
- Publikační typ
- časopisecké články MeSH
