Electrospray and APCI analysis of polyhydroxyalkaloids using positive and negative collision induced dissociation experiments in a quadrupole ion trap
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Abstract:
Atmospheric pressure chemical ionisation (APCI) and electrospray (ES) are compared as ion sources in the analysis of polyhydroxyalkaloids (PHAs) by liquid chromatography mass spectrometry (LC-MS) and collision induced dissociation (CID) product ion spectra, from tandem mass spectrometry (MS-MS) experiments in a quadrupole ion trap, are reported for 12 naturally occurring PHAs. APCI was found to be a more useful source than ES, as APCI could be used to generate deprotonated molecule ions in negative mode and for some isomeric PHAs the negative CID product ion spectra were more diagnostic than the positive product ion spectra. On-column detection limits were also approximately 32 times lower by positive APCI than ES. The work provides data that will facilitate screening and characterisation of this group of important natural products in plant and fungal extracts.Keywords:
Atmospheric-pressure chemical ionization
Collision-induced dissociation
Quadrupole ion trap
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Abstract Recently, linear ion traps (LITs) have been combined with quadrupole (Q), time‐of‐flight (TOF) and Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometery (MS). LITs can be used either as ion accumulation devices or as commercially available, stand‐alone mass spectrometers with MS n capabilities. The combination of triple quadrupole MS with LIT technology in the form of an instrument of configuration QqLIT, using axial ejection, is particularly interesting, because this instrument retains the classical triple quadrupole scan functions such as selected reaction monitoring (SRM), product ion (PI), neutral loss (NL) and precursor ion (PC) while also providing access to sensitive ion trap experiments. For small molecules, quantitative and qualitative analysis can be performed using the same instrument. In addition, for peptide analysis, the enhanced multiply charged (EMC) scan allows an increase in selectivity, while the time‐delayed fragmentation (TDF) scan provides additional structural information. Various methods of operating the hybrid instrument are described for the case of the commercial Q TRAP (AB/MDS Sciex) and applications to drug metabolism analysis, quantitative confirmatory analysis, peptides analysis and automated nanoelectrospray (ESI‐chip‐MS) analysis are discussed. Copyright © 2004 John Wiley & Sons, Ltd.
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Triple quadrupole mass spectrometers are generally considered the instrument of choice for quantitative analysis. However, for the analysis of large peptides we have encountered some cases where, as the data presented here would indicate, ion trap mass spectrometers may be a good alternative. In general, specificity and sensitivity in bioanalytical liquid chromatography/mass spectrometry (LC/MS) assays are achieved via tandem MS (MS/MS) utilizing collision-induced dissociation (CID) while monitoring unique precursor to product ion transitions (i.e. selected reaction monitoring, SRM). Due to the difference in CID processes, triple quadrupoles and ion traps often generate significantly different fragmentation spectra of product ion species and intensities. The large peptidic analytes investigated here generated fewer fragments with higher relative abundance on the ion trap as compared to those generated on the triple quadrupole, resulting in lower limits of detection on the ion trap.
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Fragmentation
Hybrid mass spectrometer
Top-down proteomics
Collision-induced dissociation
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Abstract A novel LC/MS/MS method that uses multiple ion monitoring (MIM) as a survey scan to trigger the acquisition of enhanced product ions (EPI) on a hybrid quadrupole‐linear ion trap mass spectrometer (Q TRAP) was developed for drug metabolite identification. In the MIM experiment, multiple predicted metabolite ions were monitored in both Q1 and Q3. The collision energy in Q2 was set to a low value to minimize fragmentation. Results from analyzing ritonavir metabolites in rat hepatocytes demonstrate that MIM‐EPI was capable of targeting a larger number of metabolites regardless of their fragmentation and retained sensitivity and duty cycle similar to multiple reaction monitoring (MRM)‐EPI. MIM‐based scanning methods were shown to be particularly useful in several applications. First, MIM‐EPI enabled the sensitive detection and MS/MS acquisition of up to 100 predicted metabolites. Second, MIM‐MRM‐EPI was better than MRM‐EPI in the analysis of metabolites that undergo either predictable or unpredictable fragmentation pathways. Finally, a combination of MIM‐EPI and full‐scan MS (EMS), as an alternative to EMS‐EPI, was well suited for routine in vitro metabolite profiling. Overall, MIM‐EPI significantly enhanced the metabolite identification capability of the hybrid triple quadrupole‐linear ion trap LC/MS. Copyright © 2008 John Wiley & Sons, Ltd.
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Abstract A new type of quadrupole linear ion trap mass spectrometer, Q TRAP™ LC/MS/MS system (Q TRAP™), was evaluated for its performance in two studies: firstly, the in vitro metabolism of gemfibrozil in human liver microsomes, and, secondly, the quantification of propranolol in rat plasma. With the built‐in information‐dependent‐acquisition (IDA) software, the instrument utilizes full scan MS in the ion trap mode and/or constant neutral loss scans as survey scans to trigger product ion scan (MS 2 ) and MS 3 experiments to obtain structural information of drug metabolites ‘on‐the‐fly’. Using this approach, five metabolites of gemfibrozil were detected in a single injection. This instrument combines some of the unique features of a triple quadrupole mass spectrometer, such as constant neutral loss scan, precursor ion scan and multiple reaction monitoring (MRM), together with the capability of a three‐dimensional ion trap. Therefore, it becomes a powerful instrument for metabolite identification. The fast duty cycle in the ion trap mode allows the use of full product ion scan for quantification. For the quantification of propranolol, both MRM mode and full product ion scan in the ion trap mode were employed. Similar sensitivity, reproducibility and linearity values were established using these two approaches. The use of the product ion scan mode for quantification provided a convenient tool in selecting transitions for improving selectivity during the method development stage. Copyright © 2003 John Wiley & Sons, Ltd.
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Selected ion monitoring
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The application of a new hybrid RF/DC quadrupole-linear ion trap mass spectrometer to support drug metabolism and pharmacokinetic studies is described. The instrument is based on a quadrupole ion path and is capable of conventional tandem mass spectrometry (MS/MS) as well as several high-sensitivity ion trap MS scans using the final quadrupole as a linear ion trap. Several pharmaceutical compounds, including trocade, remikiren and tolcapone, were used to evaluate the capabilities of the system with positive and negative turbo ionspray, using either information-dependent data acquisition (IDA) or targeted analysis for the screening, identification and quantification of metabolites. Owing to the MS/MS in-space configuration, quadrupole-like CID spectra with ion trap sensitivity can be obtained without the classical low mass cutoff of 3D ion traps. The system also has MS(3) capability which allows fragmentation cascades to be followed. The combination of constant neutral loss or precursor ion scan with the enhanced product ion scan was found to be very selective for identifying metabolites at the picogram level in very complex matrices. Owing to the very high cycle time and, depending on the mass range, up to eight different MS experiments could be performed simultaneously without compromising chromatographic performance. Targeted product ion analysis was found to be complementary to IDA, in particular for very low concentrations. Comparable sensitivity was found in enhanced product ion scan and selected reaction monitoring modes. The instrument is particularly suitable for both qualitative and quantitative analysis.
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Collision induced dissociation (CID) in a quadrupole ion trap mass spectrometer using the conventional 30 ms activation time is compared with high amplitude short time excitation (HASTE) CID using 2 ms and 1 ms activation times. As a result of the shorter activation times, dissociation of the parent ions using the HASTE CID technique requires resonance excitation voltages greater than conventional CID. After activation, the rf trapping voltage is lowered to allow product ions below the low mass cut-off to be trapped. The HASTE CID spectra are notably different from those obtained using conventional CID and can include product ions below the low mass cut-off for the parent ions of interest. The MS/MS efficiencies of HASTE CID are not significantly different when compared with the conventional 30 ms CID. Similar results were obtained with a two-dimensional (linear) ion trap and a three-dimensional ion trap.
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The use of a Q-q-Q(linear ion trap) instrument to obtain product ion spectra is described. The instrument is based on the ion path of a triple quadrupole mass spectrometer with Q3 operable as either a conventional RF/DC quadrupole mass filter or a linear ion trap mass spectrometer with axial ion ejection. This unique ion optical arrangement allows de-coupling of precursor ion isolation and fragmentation from the ion trap itself. The result is a high sensitivity tandem mass spectrometer with triple quadrupole fragmentation patterns and no inherent low mass cut-off. The use of the entrance RF-only section of the instrument as accumulation ion trap while the linear ion trap mass spectrometer is scanning enhances duty cycles and results in increased sensitivities by as much as a factor of 20. The instrument is also capable of all of the triple quadrupole scans including multiple-reaction monitoring (MRM) as well as precursor and constant neutral loss scanning. The high product ion scanning sensitivity allows the recording of useful product ion spectra near the MRM limit of quantitation.
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Quadrupole ion trap
Trap (plumbing)
Top-down proteomics
Posttranslational modification
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Mass spectrometric identification and characterization of growth-promoting anabolic-androgenic steroids in biological matrices has been a major task for doping control as well as food safety laboratories. The fragmentation behavior of stanozolol, its metabolites 17-epistanozolol, 3'-OH-stanozolol, 4alpha-OH-stanozolol, 4beta-OH-stanozolol, 17-epi-16alpha-OH-stanozolol, 16alpha-OH-stanozolol, 16beta-OH-stanozolol, as well as the synthetic analogues 4-dehydrostanozolol, 17-ketostanozolol, and N-methyl-3'-OH-stanozolol, was investigated after positive electrospray ionization and subsequent collision-induced dissociation utilizing a quadrupole-linear ion trap and a novel linear ion trap-orbitrap hybrid mass spectrometer. Stable isotope labeling, H/D-exchange experiments, MS3 analyses and high-resolution/high mass accuracy measurements of fragment ions were employed to allow proposals for charge-driven as well as charge-remote fragmentation pathways generating characteristic product ions of stanozolol at m/z 81, 91, 95, 105, 119, 135 and 297 and 4-hydroxylated stanozolol at m/z 145. Fragment ions were generated by dissociation of the steroidal A- and B-ring retaining the introduced charge within the pyrazole function of stanozolol and by elimination of A- and B-ring fractions including the pyrazole residue. In addition, a charge-remote fragmentation causing the neutral loss of methanol was observed, which was suggested to be composed by the methyl residue at C-18 and the hydroxyl function located at C-17.
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Orbitrap
Collision-induced dissociation
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Ion trapping
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Quadrupole ion trap
Fragmentation
Ion trapping
Hybrid mass spectrometer
Quadrupole mass analyzer
Tandem
Trap (plumbing)
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