Pharmaceutical metabolite profiling using quadrupole/ion mobility spectrometry/time‐of‐flight mass spectrometry

The use of hybrid quadrupole ion mobility spectrometry time‐of‐flight mass spectrometry (Q/IMS/TOFMS) in the metabolite profiling of leflunomide (LEF) and acetaminophen (APAP) is presented. The IMS drift times (T_d) of the drugs and their metabolites were determined in the IMS/TOFMS experiments and correlated with their exact monoisotopic masses and other in silico generated structural properties, such as connolly molecular area (CMA), connolly solvent‐excluded volume (CSEV), principal moments of inertia along the X, Y and Z Cartesian coordinates (MI‐X, MI‐Y and MI‐Z), inverse mobility and collision cross‐section (CCS). The correlation of T_d with these parameters is presented and discussed. IMS/TOF tandem mass spectrometry experiments (MS² and MS³) were successfully performed on the N‐acetyl‐p‐benzoquinoneimine glutathione (NAPQI‐GSH) adduct derived from the in vitro microsomal metabolism of APAP. As comparison, similar experiments were also performed using hybrid triple quadrupole linear ion trap mass spectrometry (QTRAPMS) and quadrupole time‐of‐flight mass spectrometry (QTOFMS). The abilities to resolve the product ions of the metabolite within the drift tube and fragment the ion mobility resolved product ions in the transfer travelling wave‐enabled stacked ring ion guide (TWIG) demonstrated the potential applicability of the Q/IMS/TOFMS technique in pharmaceutical metabolite profiling. Copyright © 2009 John Wiley & Sons, Ltd.     

Quantification,confirmation and screening capability of UHPLC coupled to triple quadrupole and hybrid quadrupole time‐of‐flight mass spectrometry in pesticide residue analysis

The potential of three mass spectrometry (MS) analyzers (triple quadrupole, QqQ; time of flight, TOF; and quadrupole time of flight, QTOF) has been investigated and compared for quantification, confirmation and screening purposes in pesticide residue analysis of fruit and vegetable samples. For this purpose, analytical methodology for multiresidue determination of 11 pesticides, taken as a model, has been developed and validated in nine food matrices for the three mass analyzers coupled to ultra high pressure liquid chromatography. In all cases, limits of quantification around 0.01 mg/kg were reached, fulfilling the most restrictive case of baby‐food analysis. Regarding absolute sensitivity, the lower limits of detection were obtained, as expected, for QqQ (100 fg), whereas slightly higher limits (300 fg) were obtained for both TOF and QTOF. Confirmative capacity of each analyzer was studied for each analyte based on the identification points (IPs) criterion, useful for a comprehensive comparison. QTOF mass analyzer showed the highest confirmatory capacity, although QqQ normally led to sufficient number of IPs, even at lower concentration levels. The potential of TOF MS was also investigated for screening purposes. To this aim, around 50 commercial fruits and vegetables samples were analyzed, searching for more than 400 pesticides. TOF MS proved to be an attractive analytical tool for rapid detection and reliable identification of a large number of pesticides thanks to the full spectrum acquisition at accurate mass with satisfactory sensitivity. This process is readily boosted when combined with specialized software packages, together with theoretical exact mass databases. Several pesticides (e.g. carbendazim in citrus and indoxacarb in grape) were detected in the samples. Further unequivocal confirmation of the identity was performed using reference standards and/or QTOF MS/MS experiments. Copyright © 2010 John Wiley & Sons, Ltd.     

Optimization of a quadrupole ion storage trap as a source for time‐of‐flight mass spectrometry

Designs of a quadrupole ion trap (QIT) as a source for time‐of‐flight (TOF) mass spectrometry are evaluated for mass resolution, ion trapping, and laser activation of trapped ions. Comparisons are made with the standard hyperbolic electrode ion trap geometry for TOF mass analysis in both linear and reflectron modes. A parallel‐plate design for the QIT is found to give significantly improved TOF mass spectrometer performance. Effects of ion temperature, trapped ion cloud size, mass, and extraction field on mass resolution are investigated in detail by simulation of the TOF peak profiles. Mass resolution (m/Δm) values of several thousand are predicted even at room temperature with moderate extraction fields for the optimized design. The optimized design also allows larger radial ion collection size compared with the hyperbolic ion trap, without compromising the mass resolution. The proposed design of the QIT also improves the ion–laser interaction volume and photon collection efficiency for fluorescence measurements on trapped ions. Copyright © 2011 John Wiley & Sons, Ltd.     

Evaluation and validation of an ion mobility quadrupole time‐of‐flight mass spectrometry pesticide screening approach

An ion mobility quadrupole time‐of‐flight mass spectrometry‐based pesticide suspect screening methodology was developed and validated covering 20 plant‐derived food matrices deriving from six commodity groups of different complexity according to the actual European Commission document SANTE/11813/2017 applying a QuEChERS sample preparation protocol. The method combines ultra‐performance liquid chromatography, traveling wave ion mobility, and quadrupole time‐of‐flight mass spectrometry. Besides the determination of the physicochemical property collision cross‐section and the establishment of a corresponding scientific suspect screening database comprising 280 pesticides for several pesticides, different protomers, sodium adducts, as well as dimers were identified in ion mobility spectrometry traces. Additionally, collision cross‐section values were included in the validation requirements regarding chromatography and mass spectrometry for the detection of pesticides. A collision cross‐section value window was analyzed within a tolerable error of ±2%. For this cross‐matrix validation, screening detection limits were determined at concentration levels of 0.100 mg/kg (84% of the original pesticide scope), 0.010 mg/kg (56%), and 0.001 mg/kg (21%). By application of ion mobility spectrometry, the compound identification was improved due to independence of commodity of concern and concentration levels of analyte molecules, as false assignments are reduced by application of a collision cross‐section range.     

Rapid identification of gallotannins from Chinese galls by matrix‐assisted laser desorption/ionization time‐of‐flight quadrupole ion trap mass spectrometry

Chinese gall, a conventional traditional Chinese medicine, contains high levels of gallotannins. A rapid method for direct analysis of the gallotannins without using any troublesome sample pretreatments was developed using matrix‐assisted laser desorption/ionization time‐of‐flight quadrupole ion trap mass spectrometry (MALDI‐QIT‐TOF MS) to successfully identify the gallotannin components in the crude extract of Chinese galls within several minutes. The high quality of the MS and MS² spectra acquired clearly showed that hydrolysable tannins in Chinese galls were identified as a series of the gallotannins with degrees of polymerization (DP) of 4–11 galloyl units. The MS² data indicated that the identified gallotannins with DP of 4–7 galloyl units had clear fragmentation with loss of 1–5 galloyl units which were further deprived of 1–3 water moieties. This technique may be used for rapid evaluation and screening of hydrolysable tannins in medicinal plants. Copyright © 2009 John Wiley & Sons, Ltd.     

An introduction to hybrid ion trap/time‐of‐flight mass spectrometry coupled with liquid chromatography applied to drug metabolism studies

Metabolism studies play an important role at various stages of drug discovery and development. Liquid chromatography combined with mass spectrometry (LC/MS) has become a most powerful and widely used analytical tool for identifying drug metabolites. The suitability of different types of mass spectrometers for metabolite profiling differs widely, and therefore, the data quality and reliability of the results also depend on which instrumentation is used. As one of the latest LC/MS instrumentation designs, hybrid ion trap/time‐of‐flight MS coupled with LC (LC‐IT‐TOF‐MS) has successfully integrated ease of operation, compatibility with LC flow rates and data‐dependent MSⁿ with high mass accuracy and mass resolving power. The MSⁿ and accurate mass capabilities are routinely utilized to rapidly confirm the identification of expected metabolites or to elucidate the structures of uncommon or unexpected metabolites. These features make the LC‐IT‐TOF‐MS a very powerful analytical tool for metabolite identification. This paper begins with a brief introduction to some basic principles and main properties of a hybrid IT‐TOF instrument. Then, a general workflow for metabolite profiling using LC‐IT‐TOF‐MS, starting from sample collection and preparation to final identification of the metabolite structures, is discussed in detail. The data extraction and mining techniques to find and confirm metabolites are discussed and illustrated with some examples. This paper is directed to readers with no prior experience with LC‐IT‐TOF‐MS and will provide a broad understanding of the development and utility of this instrument for drug metabolism studies. Copyright © 2012 John Wiley & Sons, Ltd.     

Use of a quadrupole linear ion trap mass spectrometer in metabolite identification and bioanalysis

A new type of quadrupole linear ion trap mass spectrometer, Q TRAP trade mark LC/MS/MS system (Q TRAP trade mark ), 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.     

Elucidation of artefacts in proton transfer reaction time‐of‐flight mass spectrometers

We present an effective procedure to differentiate instrumental artefacts, such as parasitic ions, memory effects, and real trace impurities contained in inert gases. Three different proton transfer reaction mass spectrometers were used in order to identify instrument‐specific parasitic ions. The methodology reveals new nitrogen‐ and metal‐containing ions that up to date have not been reported. The parasitic ion signal was dominated by [N₂]H⁺ and [NH₃]H⁺ rather than by the common ions NO⁺ and O₂⁺. Under dry conditions in a proton transfer reaction quadrupole interface time‐of‐flight mass spectrometer (PTR‐QiTOF), the ion abundances of [N₂]H⁺ were elevated compared with the signals in the presence of humidity. In contrast, the [NH₃]H⁺ ion did not show a clear humidity dependency. On the other hand, two PTR‐TOF1000 instruments showed no significant contribution of the [N₂]H⁺ ion, which supports the idea of [N₂]H⁺ formation in the quadrupole interface of the PTR‐QiTOF. Many new nitrogen‐containing ions were identified, and three different reaction sequences showing a similar reaction mechanism were established. Additionally, several metal‐containing ions, their oxides, and hydroxides were formed in the three PTR instruments. However, their relative ion abundancies were below 0.03% in all cases. Within the series of metal‐containing ions, the highest contribution under dry conditions was assigned to the [Fe(OH)₂]H⁺ ion. Only in one PTR‐TOF1000 the Fe⁺ ion appeared as dominant species compared with the [Fe(OH)₂]H⁺ ion. The present analysis and the resulting database can be used as a tool for the elucidation of artefacts in mass spectra and, especially in cases, where dilution with inert gases play a significant role, preventing misinterpretations.     

Rapid separation and identification of furocoumarins in Angelica dahurica by high‐performance liquid chromatography with diode‐array detection,time‐of‐flight mass spectrometry and quadrupole ion trap mass spectrometry

High‐performance liquid chromatography with diode‐array detection (HPLC/DAD), time‐of‐flight mass spectrometry (HPLC/TOFMS) and quadrupole ion trap mass spectrometry (HPLC/QITMS) were used for separation, identification and structural analysis of furocoumarins in Angelica dahurica. Two furocoumarins (imperatorin and isoimperatorin) in Angelica dahurica extract were identified unambiguously by comparing their relative retention times, characteristic ultraviolet information and accurate mass measurement. A formula database of known furocoumarins in Angelica dahurica was established, against which the other 21 furocoumarins were identified effectively based on the accurate extract masses and formulae acquired by HPLC/TOFMS. In order to distinguish the isomers, multi‐stage mass spectrometry (MSⁿ, ion trap mass spectrometry) was used. General fragmentation behavior of the furocoumarins in the ion trap mass spectrometer was studied by the two furocoumarin standards, and their fragmentation rules in MSⁿ spectra were summarized. These deduced fragmentation rules of furocoumarins were successfully implemented in distinguishing the three groups of isomers in Angelica dahurica by HPLC/QITMS. By using the three different analytical techniques, 23 furocoumarins in Angelica dahurica were tentatively identified within 30 min. Finally, HPLC/TOFMS fingerprints of Angelica dahurica were established by which it can be concluded that a rapid and effective method based on the three analytical techniques for identification of chemical components was established. This can provide help for further quality control of Angelica dahurica and pharmacology mechanism study of furocoumarins in Angelica dahurica. Copyright © 2009 John Wiley & Sons, Ltd.