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Ion-trap Mass Spectrometer (ion-trap + mass_spectrometer)
Selected AbstractsPeptides of human gingival crevicular fluid determined by HPLC-ESI-MSEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 6 2005Elisabetta Pisano The acidic-soluble protein content of human gingival crevicular fluid was analyzed by reverse-phase high-performance liquid chromatography (RP-HPLC), and the eluent deriving from the chromatography separation was directly introduced into an ion-trap mass spectrometer through electrospray ionization (ESI-IT MS). By this technique the molecular weight of peptides/proteins was determined with a precision of ,,1/10,000 amu. On the basis of the chromatographic behavior and the knowledge of the molecular mass value, some peptides and proteins soluble in acidic solution were unambiguously recognized. Besides high quantities of human serum albumin, , -defensins 1,4 and minor amounts of cystatin A, statherin, basic PB salivary peptide and other unidentified components were detected. The presence of , -defensins in gingival crevicular fluid is in agreement with their relevant contribution to protein composition deriving from granulocyte secretions. Other peptides and proteins abundant in human saliva, such as proline-rich proteins (PRPs) and histatins, were not detected in gingival crevicular fluid. Further investigations will be necessary to establish the origin of statherin and PB salivary peptide in gingival crevicular fluid. [source] Rapid classification of enzymes in cleaning products by hydrolysis, mass spectrometry and linear discriminant analysisRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 22 2008Miriam Beneito-Cambra A method for the rapid classification of proteases, lipases, amylases and cellulases used as enhancers in cleaning products, based on precipitation with acetone, hydrolysis with HCl, dilution of the hydrolysates with ethanol, and direct infusion into the electrospray ion source of an ion-trap mass spectrometer, has been developed. The abundances of the ([M+H]+ ions of the amino acids, from the hydrolysates of both the enzyme industrial concentrates and the detergent bases spiked with them, were used to construct linear discriminant analysis models, capable of distinguishing between the enzyme classes. For this purpose, the variables were normalized as follows: (A) the ion abundance of each amino acid was divided by the sum of the ion abundances of all the amino acids in the corresponding mass spectrum; (B) the ratios of pairs of ion abundances were obtained by dividing the ion abundance of each amino acid by each one of the ion abundances of the other 17 amino acids in the corresponding mass spectrum. Using normalization procedure B, excellent class-resolution between proteases, lipases, amylases and cellulases was achieved. In all cases, enzymes in industrial concentrates and manufactured cleaning products were correctly classified with >98% assignment probability. Copyright © 2008 John Wiley & Sons, Ltd. [source] Metabolism of a sulfur-containing heteroarotionoid antitumor agent, SHetA2, using liquid chromatography/tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 21 2008Zhongfa Liu SHetA2 {[(4-nitrophenyl)amino][2,2,4,4-tetramethylthiochroman-6-yl)amino]methanethione], NSC 726189}, a sulfur-containing heteroarotinoid, selectively inhibits cancer cell growth and induces apoptosis without activation of nuclear retinoic acid receptors (RARs). The objective of this study was to investigate its in vitro metabolism in rat and human liver microsomes and in vivo metabolism in the mouse and rat using liquid chromatography-ultraviolet/multi-stage mass spectrometry (LC-UV/MSn) on an ion-trap mass spectrometer coupled with a photo-diode array (PDA) detector. In vitro, in the absence of glutathione (GSH), oxidation of the four aliphatic methyl groups of SHetA2 yielded one mono-, two di-, and one tri-hydroxylated SHetA2 metabolites, which were identified based on their UV and multi-stage mass spectra. In the presence of GSH, in addition to these primary oxidative metabolites, four GSH adducts of SHetA2 and a novel rare form thioether GSH adduct was detected and characterized. In vivo, the monohydroxylated SHetA2 metabolites were also detected in mouse and rat plasma and two GSH adducts were detected in rat liver following intravenous (i.v.) bolus administration of SHetA2 at 40,mg/kg. Copyright © 2008 John Wiley & Sons, Ltd. [source] Determination of aerobic-anaerobic metabolism-related compounds in a Chaoborus flavicans population by infusion ion trap mass spectrometry of extracts of individual larvaeRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 6 2006Maria da Graça Gama Melão 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,µL water and deproteinized with a spin-filter; 50,µL aliquots were mixed with 50,µL 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,µM for pyruvate and lactate to 200,µM for acetate and glycerol. The MS2 ion-trap spectra obtained at pH 7 (ammonium acetate buffer) were used to distinguish maleate (cis -2-butenedioic), which gave [M,CO2,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. Copyright © 2006 John Wiley & Sons, Ltd. [source] Enantiomer discrimination of peptides by tandem mass spectrometry: influence of the peptide sequence on chiral recognitionRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 22 2004Christoph Czerwenka The enantiomer discrimination of peptides by electrospray ionization tandem mass spectrometry is described. A cinchona alkaloid derivative, tert -butylcarbamoylquinine, is used as chiral selector. The chiral selector forms diastereomeric complexes with the peptide enantiomers in the liquid phase (methanolic solution), which are then transferred to the gas phase, where their dissociation behaviour is studied in an ion-trap mass spectrometer. Different degrees of dissociation of the diastereomeric complexes allow for the discrimination of the peptide enantiomers. The influence of the peptide sequence on enantiomer discrimination is discussed and molecular recognition information is derived by comparing the results obtained for related peptides. For dipeptides, small amino acid residues at the N-terminus and bulky side chains at the C-terminus were found to enhance chiral recognition, while for tripeptides the effects were rather irregular. Copyright © 2004 John Wiley & Sons, Ltd. [source] Determination of atrazine, deethylatrazine and simazine in water at parts-per-trillion levels using solid-phase extraction and gas chromatography/ion trap mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2003W. T. Ma Methods for trace analysis of atrazine and simazine in water have been developed by using stable-isotope dilution with detection by gas chromatography/mass spectrometry. D5 -Atrazine was used as the internal standard for the determination of atrazine and deethylatrazine, while 13C3 -simazine was used for simazine analysis. Water samples were fortified with known amounts of the internal standards and submitted to solid-phase extraction with a C18 bonded-silica cartridge. A gas chromatograph coupled with an ion-trap mass spectrometer was used to analyze the water sample extracts. Method detection limits were 38 parts-per-trillion (ppt) for atrazine and deethylatrazine and 75 ppt for simazine. The accuracy of the method, represented by relative analytical errors, was less than 15%, and the method precision was less than 5% (relative standard deviation, n,=,9). The method was successfully applied to analyze surface water samples collected from a reservoir and a river at ppt levels. Copyright © 2003 John Wiley & Sons, Ltd. [source] A novel nanoflow interface for atmospheric pressure ionization mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2003Atsumu HirabayashiArticle first published online: 23 JAN 200 A novel spray-ionization technique for nanoflow liquid chromatography/mass spectrometry (nLC/MS) has been developed by modifying the sonic spray ionization (SSI) technique. A solution from a tapered fused-silica capillary is sprayed by a gas flow coaxial to the capillary, and ions produced are analyzed with an ion-trap mass spectrometer. The ion intensity is shown to have a steep threshold at a low gas velocity and to be much less dependent on the gas velocity than that of conventional SSI, in which the ion intensity is strongly dependent on the gas velocity and reaches its maximum at sonic velocity. Thus, we conclude that the concentration of charge in the solution at the tapered capillary tip with an inner diameter of 15,,m is almost at saturation so that charged droplets are produced from the solution by electrical force, rather than by sheer stress due to the gas flow. The ions are readily produced from these charged droplets. Preliminary results are compared with results obtained with a miniaturized electrospray unit. Copyright © 2003 John Wiley & Sons, Ltd. [source] Studies on azaspiracid biotoxins.RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2002In this report, the mass spectral analysis of azaspiracid biotoxins is described. Specifically, the collision-induced dissociation (CID) behavior and differences between CID spectra obtained on a triple-quadrupole, a quadrupole time-of-flight, and an ion-trap mass spectrometer are addressed here. The CID spectra obtained on the triple-quadrupole mass spectrometer allowed the classification of the major product ions of the five investigated compounds (AZA 1,5) into five distinct fragment ion groups, according to the backbone cleavage positions. Although the identification of unknown azaspiracids was difficult based on CID alone, the spectra provided sufficient structural information to allow confirmation of known azaspiracids in marine samples. Furthermore, we were able to detect two new azaspiracid analogs (AZA 1b and 6) in our samples and provide a preliminary structural analysis. The proposed dissociation pathways under tandem mass spectrometry (MS/MS) conditions were confirmed by a comparison with accurate mass data from electrospray quadrupole time-of-flight MS/MS experiments. Regular sequential MSn analysis on an ion-trap mass spectrometer was more restricted in comparison to the triple-quadrupole mass spectrometer, because the azaspiracids underwent multiple [M,+,H,,,nH2O]+ (n,=,1,6) losses from the precursor ion under CID. Thus, the structural information obtained from MSn experiments was somewhat limited. To overcome this limitation, we developed a wide-range excitation technique using a 180-u window that provided results comparable to the triple-quadrupole instrument. To demonstrate the potential of the method, we applied it to the analysis of degraded azaspiracids from mussel tissue extracts. Copyright © 2002 John Wiley & Sons, Ltd. [source] Collision-induced dissociation of glycero phospholipids using electrospray ion-trap mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2001Åsmund Larsen Characterisation of phospholipids was achieved using collision-induced dissociation (CID) with an ion-trap mass spectrometer. The product ions were compared with those obtained with a triple quadrupole mass spectrometer. In the negative ion mode the product ions were mainly sn -1 and sn -2 lyso-phospholipids with neutral loss of ketene in combination with neutral loss of the polar head group. Less abundant product ions were sn -1 and sn -2 carboxylate anions. CID using a triple quadrupole mass spectrometer, however, gave primarily the sn -1 and sn -2 carboxylate anions together with lyso-phosphatidic acid with neutral loss of water. For the ion trap a charge-remote-type mechanism is proposed for formation of the lyso-phospholipid product ions by loss of ,-hydrogen on the fatty acid moiety, electron rearrangement and neutral loss of ketene. A second mechanism involves nucleophilic attack of the phosphate oxygen on the sn -1 and sn -2 glycerol backbone to form carboxylate anions with neutral loss of cyclo lyso-phospholipids. CID (MS3 and MS4) of the lyso-phospholipids using the ion-trap gave the same carboxylate anions as those obtained with a triple quadrupole instrument where multiple collisions in the collision cell are expected to occur. The data demonstrate that phospholipid species determination can be performed by using LC/MSn with an ion-trap mass spectrometer with detection of the lyso-phospholipid anions. The ion-trap showed no loss in sensitivity in full scan MSn compared to multiple reaction monitoring data acquisition. In combination with on-line liquid chromatography this feature makes the ion-trap useful in the scanning modes for rapid screening of low concentrations of phospholipid species in biological samples as recently described (Uran S, Larsen,Å, Jacobsen PB, Skotland T. J. Chromatogr. B 2001; 758: 265). Copyright © 2001 John Wiley & Sons, Ltd. [source] A study of the electrospray ionisation and ion-trap fragmentation of [M,,,H], ions of new 3,5-disubstituted tetrahydro-2H -1,3,5-thiadiazin-2-thionesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 10 2001Roberto Martínez-Alvarez The electrospray ionisation (ESI) in negative mode of the pharmacologically significant 3,5-disubstituted tetrahydro-2H -1,3,5-thiadiazin-2-thiones, and their subsequent fragmentations using an ion-trap mass spectrometer, have been investigated. Experiments on sequential product ion fragmentations (MSn) were performed in order to elucidate the degradation pathways for these compounds. The data presented show that the fragmentation of the even-electron [M,,,H], ions could proceed through an internal nucleophilic substitution displacement. Decarboxylation and extrusion of carbon disulfide are other fragmentations observed. Copyright © 2001 John Wiley & Sons, Ltd. [source] Gas-Phase Reactivity of Metavanadate [VO3], towards Methanol and Ethanol: Experiment and TheoryCHEMISTRY - A EUROPEAN JOURNAL, Issue 31 2007Tom Waters Dr. Abstract The gas-phase reactivity of the metavanadate anion [VO3], towards methanol and ethanol was examined by a combination of ion,molecule reaction and isotope labelling experiments in a quadrupole ion-trap mass spectrometer. The experimental data were interpreted with the aid of density functional theory calculations. [VO3], dehydrated methanol to eliminate water and form [VO2(,2 -OCH2)],, which features an [,2 - C,O -OCH2]2, ligand formed by formal removal of two protons from methanol and which is isoelectronic with peroxide. [VO3], reacted with ethanol in an analogous manner to form [VO2(,2 -OCHCH3)],, as well as by loss of ethene to form [VO2(OH)2],. The calculations predicted that important intermediates in these reactions were the hydroxo alkoxo anions [VO2(OH)(OCH2R)], (R: H, CH3). These were predicted to undergo intramolecular hydrogen-atom transfer to form [VO(OH)2(,1 -OCHR)], followed by ,1 - O,,2 - C,O rearrangements to form [VO(OH)2(,2 -OCHR)],. The latter reacted further to eliminate water and generate the product [VO2(,2 -OCHR)],. This major product observed for [VO3], is markedly different from that observed previously for [NbO3], containing the heavier Group,5 congener niobium. In that case, the major product of the reaction was an ion of stoichiometry [Nb, O3, H2], arising from the formal dehydrogenation of methanol to formaldehyde. The origin of this difference was examined theoretically and attributed to the intermediate alkoxo anion [NbO2(OH)(OCH3)], preferring hydride transfer to form [HNbO2(OH)], with loss of formaldehyde. This contrasts with the hydrogen-atom-transfer pathway observed for [VO2(OH)(OCH3)],. [source] Diastereomeric differentiation of norbornene amino acid peptides by electrospray ionization tandem mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 18 2009B. Raju A new class of diastereomeric pairs of non-natural amino acid peptides derived from butyloxycarbonyl (Boc-)protected cis- (2S,3R)- and trans- (2S,3S) -, -norbornene amino acids including a monomeric pair have been investigated by electrospray ionization (ESI) tandem mass spectrometry using quadrupole time-of-flight (Q-TOF) and ion-trap mass spectrometers. The protonated cis -BocN- , -nbaa (2S,3R) (1) (,nbaa,=,, -norbornene amino acid) eliminates the Boc group to form [M+H,Boc+H]+, whereas an additional ion [M+H,C4H8]+ is formed from trans -BocN- , -nbaa (2S,3S) (2). Similarly, it is observed that the peptide diastereomers (di-, tri- and tetra-), with cis -BocN- , -nbaa (2S,3R)- at the N-terminus, initially eliminate the Boc group to form [M+H,Boc+H]+ which undergo further fragmentation to give a set of product ions that are different for the peptides with trans -BocN- , -nbaa (2S,3S)- at the N-terminus. Thus the Boc group fragments differently depending on the configuration of the amino acid present at the N-terminus. It is also observed that the peptide bond cleavage in these peptides is less favoured and most of the product ions are formed due to retro-Diels-Alder fragmentation. Interestingly, sodium-cationized peptide diastereomers mainly yield a series of retro-Diels-Alder fragment ions which are different for each diastereomer as they are formed starting from [M+Na,Boc+H]+ in peptides with cis -BocN- , -nbaa (2S,3R)- at the N-terminus, and [M+Na,C4H8]+ in peptides with trans -BocN- , -nbaa (2S,3S)- at the N-terminus. All these results clearly indicate that these diastereomeric pairs of peptides yield characteristic product ions which help distinguish the isomers. Copyright © 2009 John Wiley & Sons, Ltd. [source] | ||||||||||