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Quadrupole Ion Trap Mass Spectrometer (quadrupole + ion_trap_mass_spectrometer)
Selected AbstractsAn investigation of the homolytic saccharide cleavage of deprotonated flavonol 3- O -glycosides in a quadrupole ion trap mass spectrometerJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 8 2008Barry D. Davis Abstract The trend in the extent of homolytic saccharide cleavage is reported for a series of deprotonated flavonol 3- O -glycosides upon collision-induced dissociation (CID) in a quadrupole ion trap mass spectrometer. The second-generation product ions from the primary [Y0], and [Y0, H],, product ions were also identified. It was determined that the structure of both the aglycon and the saccharide portions of the flavonoid glycoside are pivotal in inducing radical cleavage. In contrast to earlier work on this subject reported for a smaller group of flavonols, the correlation between the degree of B-ring hydroxylation and the extent of radical saccharide cleavage showed several notable exceptions in the present work. Homolytic cleavage was also investigated in the context of using tandem mass spectrometry to identify the aglycon portions of flavonoid glycosides. Copyright © 2008 John Wiley & Sons, Ltd. [source] Using collision-induced dissociation with corrections for the ion number of degrees of freedom for quick comparisons of relative bonding strengthJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 11 2004Natalia Vinokur Abstract The number of degrees of freedom-dependent stability of ions and ion,neutral non-covalent complexes under collision-induced dissociation (CID) conditions was studied in a quadrupole ion trap mass spectrometer. It was found that the stability of ions as probed by energy-variable CID has a linear dependence on the total number of degrees of freedom for the ions (or ion,neutral complexes) with the same (or nearly the same) bonding energy. The slope of such a stability vs number of degrees of freedom dependence correlates with the binding energy. Proton-bound amine dimers display the lowest slope as they have weak bonds. Breaking covalent bonds will result in much greater slopes. In addition to the binding energy, the vibrational frequencies of the ion also affect the stability vs number of degrees of freedom behavior. Studying such a dependence of the CID stability in a system paves the way for direct relative binding energy comparisons. The application of this approach is demonstrated by testing the relative heme affinities of anti-malaria drugs and related compounds. Copyright © 2004 John Wiley & Sons, Ltd. [source] Coupling of ion-molecule reactions with liquid chromatography on a quadrupole ion trap mass spectrometerRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 8 2008Yuriy Pyatkivskyy We report for the first time a coupling of gas-phase ion-molecule reactions with chromatographic separations on a quadrupole ion trap mass spectrometer. The interface was accomplished by using a pulsed valve for the introduction of a volatile neutral into the ion trap. The pulsed valve controller is synchronized with the mass spectrometer software. The setup requires some minor modifications to the vacuum system of the commercial quadrupole ion trap but most of the modifications are external to the mass spectrometer. Two applications of this interface are described: differentiation between two phosphoglucose positional isomers and detection of a phosphopeptide in a peptide mixture. Both applications are using the reactivity of trimethoxyborate towards a phosphate moiety in the negative ion mode. The detection of phosphopeptides hinges on our findings that non-phosphorylated peptide anions do not react with trimethoxyborate. This LC/MS detection can be easily visualized in terms of selected reaction monitoring. Copyright © 2008 John Wiley & Sons, Ltd. [source] Ion motion in the rectangular wave quadrupole field and digital operation mode of a quadrupole ion trap mass spectrometer,RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 1 2006L. Ding A quadrupolar electric field driven by a rectangular wave voltage can be used for mass-selective storage and analysis. The ion motion in such an electric field is derived, and the stability of ions is presented in the a-q diagram that is commonly used for sinusoidal wave quadrupole mass spectrometry in association with the solution of the Mathieu equation. The pseudo-potential well is discussed in an approximation that leads to the relation of secular frequency to operating parameters. A scheme for a digital ion trap mass spectrometer is described, based on this theory. An ion optics simulation was performed to check the theory of resonant ejection, and to prove the feasibility of the mass scan method for a practical ion trap of such geometry. Copyright © 2005 John Wiley & Sons, Ltd. [source] Characterisation and determination of indole alkaloids in frog-skin secretions by electrospray ionisation ion trap mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2002Stephen McClean The characterisation of selected indole alkaloids in a quadrupole ion trap mass spectrometer is presented. Fragmentation profiles for tryptamine, 5-hydroxytryptamine (5-HT), N,-methyl 5-hydroxytryptamine (N,-methyl 5-HT), N,,N,-dimethyl 5-hydroxytryptamine (bufotenine), N,,N,,N,-trimethyl 5-hydroxytryptamine (5-HTQ), and N,,N,-dimethyl 5-methoxytryptamine (5-MeODMT) are presented with proposed structures given for each product ion observed. Such MSn experiments can be used to differentiate the isobaric molecular ions of the compounds 5-HTQ (M+) and 5-MeODMT (MH+). The quantitative determination of certain indole alkaloids in the skin secretions of the Australian Golden Bell frog, Litoria aurea, by LC/ESI-ion trap MS is also presented. The concentrations of 5-HT, N,-methyl 5-HT and 5-HTQ were found to be 2.68, 0.26 and 0.54,µg per,mg of skin secretion, respectively. Copyright © 2002 John Wiley & Sons, Ltd. [source] Systematic determination of ion score cutoffs based on calculated false positive rates: application for identifying ubiquitinated proteins by tandem mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 3 2008Julian Vasilescu Abstract We report a simple approach for determining ion score cutoffs that permit the confident identification of ubiquitinated proteins by tandem mass spectrometry (MS/MS). Initial experiments involving the analysis of gel bands containing multi-Ubiquitin chains with quadrupole time-of-flight and quadrupole ion trap mass spectrometers revealed that standard ion score cutoffs used for database searching were not sufficiently stringent. We also found that false positive and false negative rates (FPR and FNR) varied significantly depending on the cutoff scores used and that appropriate cutoffs could only be determined following a systematic evaluation of false positive rates. When standard cutoff scores were used for the analysis of complex mixtures of ubiquitinated proteins, unacceptably high FPR were observed. Finally, we found that FPR for ubiquitinated proteins are affected by the size of the protein database that is searched. These observations may be applicable for the study of other post-translational modifications. Copyright © 2007 John Wiley & Sons, Ltd. [source] Evaluation of axial DC offsets during scanning of a quadrupole ion trap for sensitivity improvementsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 9 2001Timothy Vaden In the normal operation of quadrupole ion trap mass spectrometers, approximately half of the trapped ions are ejected through the source endcap during a mass-selective instability scan. This reduces the sensitivity of the instrument by ,50%. In this preliminary study, a circuit was constructed that produced a dipolar DC offset on the axial modulation waveform to recover this lost ion current. A variable (0 to 10,V DC), positive and negative offset was applied to the source and detector endcap, respectively. This DC offset axially displaced the ion cloud toward the detector endcap increasing the probability of detection. Several compounds, including 11 pesticides, were evaluated. Sensitivity enhancements ranged from 13 to 97% (theoretical 100%). No spectral resolution problems were observed; however, a compound-dependent mass discrimination was observed in several cases. This mass discrimination problem is currently under investigation. Copyright © 2001 John Wiley & Sons, Ltd. [source] | ||||||||||