Screening and characterization of reactive metabolites using glutathione ethyl ester in combination with Q-trap mass spectrometry

The present study describes a new analytical approach for the detection and characterization of chemically reactive metabolites using glutathione ethyl ester (GSH-EE) as the trapping agent in combination with hybrid triple quadrupole linear ion trap mass spectrometry. Polarity switching was applied between a negative precursor ion (PI) survey scan and the positive enhanced product ion (EPI) scan. The negative PI scan step was carried out monitoring the anion at m/z 300, corresponding to deprotonated gamma-glutamyl-dehydroalanyl-glycine ethyl ester originating from the GSH-EE moiety. Samples resulting from incubations in the presence of GSH-EE were cleaned and concentrated by solid-phase extraction, followed by the PI-EPI analysis. Unambiguous identification of GSH-EE-trapped reactive metabolites was greatly facilitated by the unique survey scan of the anion at m/z 300, which achieved less background interference, in particular, from endogenous glutathione adducts present in human liver microsomes. Further structural characterization was achieved by analyzing positive MS(2) spectra that featured rich fragments without mass cutoff and were acquired in the same liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. The effectiveness and reliability of this approach was evaluated using a number of model compounds in human liver microsomal incubations, including acetaminophen, amodiaquine, carbamazepine, 4-ethylphenol, imipramine and ticlopidine. In addition, iminoquinone reactive metabolites of mianserin were trapped and characterized for the first time using this method. Compared to neutral loss (NL) scanning assays using GSH as the trapping agent, the results have demonstrated superior selectivity, sensitivity, and reliability of this current approach.     

Fragmentation studies on the antibiotic avilamycin A using ion trap mass spectrometry

A comprehensive study on the fragmentation pattern of the antimicrobial growth promoter avilamycin A was conducted in a quadrupole ion trap mass spectrometer equipped with an electrospray ionization (ESI) source. Performing multiple-stage experiments on the deprotonated molecule (m/z 1401) and its principal product ions showed that a sequential shortening of the oligosaccharide backbone took place, which can be attributed to the localization of the negative charge in the terminal dichloroisoeverninic acid. Under (+)-ESI conditions, avilamycin A readily formed an intense sodium-cationized molecule, [M + Na](+) (m/z 1425). Structural elucidation of the second-, third- and fourth-generation fragment ions revealed that all of the structures shared a common molecular portion comprising a central monosaccharide. This observation allowed us to assign confidently the complexation site of the alkali metal cation. In addition to the monosodiated molecule, the full-scan mass spectral acquisition also yielded a less abundant disodiated molecule, [M - H + 2Na](+) (m/z 1447). Multiple-stage experiments on this ion indicated that the second sodium ion compensates for the negative charge located at either of two positions within the molecule. While deprotonation of the phenolic hydroxyl group in the dichloroisoeverninic acid moiety was suggested to be driven by charge stabilization in the aromatic ring (in analogy with the deprotonated molecule in the (-)-ESI mode), the deprotonation at an alpha-carbon of an ester side-chain substituent in the oligosaccharide part was believed to provide a stable chelation-like coordination site for the cation.     

Analysis of rare-earth elements in soil sample by using laser-ablation ion trap mass spectrometry

Laser-ablation ion trap mass spectrometry (LA-ITMS) is applied for the analysis of rare-earth elements in soil samples. The target elements studied in this work were ytterbium (Yb) and samarium (Sm). The isotopic compositions of these elements were analyzed for standard samples with chip shape, the western phosphate rock sample (NIST SRM-694), and soil samples collected near our laboratory. For metal samples of Sm and Yb, isotopes of these elements as well as oxide forms were clearly identified. For the case of soil samples only a tentative assignment on the mass peaks were performed due to the complicated mass spectra that originated from the oxide forms of various rare-earth elements.     

Rapid screening and characterization of drug metabolites using a new quadrupole-linear ion trap mass spectrometer

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.     

Multistep mass spectrometry of heterocyclic amines in a quadrupole ion trap mass analyser

The fragmentation of heterocyclic amines (HAs) in an ion trap was studied by means of the infusion of methanolic solutions containing the compounds under assay, and using an atmospheric pressure chemical ionization (APCI) as ion source. The MS(n) spectra obtained for compounds included in the same family, either aminoimidazoazaarenes (AIAs) or carbolines, were compared in order to propose fragmentation pathways for each HA. Moreover, labelled AIAs were used to establish the mechanisms. The protonated molecule was always obtained, but subsequent fragmentation was different for both families. In the case of AIAs, major product ions came from the fragmentation of the aminoimidazole moiety, thus the base peak in MS(2) corresponded to the loss of the methyl group, and losses of C(2)NH(3) and CN(2)H(2) were also observed. Further fragmentation occurred in the heterocyclic rings, mainly with losses of HCN and CH(3)CN. For carbolines, the most important product ions came from the loss of ammonia, except for harman and norharman, the loss of a methyl group for methylated carbolines or the loss of diverse fragments from the heterocyclic rings. In some cases, ion-molecule reactions into the ion trap were observed. For instance, for AalphaC or MeAalphaC one ion originating from these reactions corresponded to the base peak.     

稳定图的测定与矩形离子阱质谱性能分析

从理论上讲, 离子阱质谱仪的性能是由阱内电场分布决定的,而电场分布又是由组成离子阱的电极几何结构和离子阱工作电压决定的. 对于矩形离子阱, 即使不考虑其几何结构的偏差, 其阱内的电场分布一般也很复杂. 在矩形离子阱内, 除四极电场外, 还包含多种成分的其他各种高阶场, 它们直接影响离子在阱内的运动轨迹和离子阱质谱的性能. 由于各种电场成分对离子阱内离子运动的影响非常复杂, 还很难从数学上给出精确的解析解, 使得目前从理论上还无法预测高阶场成分对质谱性能的影响. 本工作通过测定不同几何结构的矩形离子阱的稳定图, 从实验上比较了不同场半径, 即不同电场分布条件下的离子阱质谱性能的差别. 实验中, 通过改变离子阱的几何比例结构, 详细测定了不同结构的矩形离子阱的稳定图特征, 并与实验测得的质谱分析结果进行比较. 同时, 我们还详细介绍了矩形离子阱质谱的稳定图的测定方法, 并根据得到的不同情况下的稳定图结构分析了离子阱的质谱性能. 研究结果表明： 可以通过比较试验得到的稳定图结构来判断其离子阱质谱仪的性能如质量分辨能力等. 此外, 实验结果还发现： 对于y方向拉伸结构的矩形离子阱, 其实验绘制得到的是不完整的稳定图. 但根据稳定图边界的特点, 通过采用四极直流电压调制的方法, 可以对y方向拉伸结构的矩形离子阱的性能进行改善, 极大地提高了阱的质量分辨能力.     

Determination of organotins in water by micro liquid chromatography–electrospray/ion trap mass spectrometry

Due to the varying toxicity the species of organotins in their widespread applications, it is important for analytical methods to address their speciation. Traditional methods call for the hydrolysis and subsequent derivatization of the organotins before analysis. These methods can be time‐consuming, derivatization can be incomplete and high levels of background interference produce difficulties in identification and quantification. The use is described of a non‐derivatization and non‐hydrolysis micro‐liquid chromatography–electrospray/ion trap mass spectrometry for separation and detection of the organotins. Copyright © 1999 John Wiley & Sons, Ltd.     

Multi-parameter investigation of tandem mass spectrometry in a linear ion trap using response surface modelling

The feasibility of experimental design in combination with subsequent response surface modelling was illustrated for the prediction and interpretation of tandem mass spectrometric (MS/MS) fragmentation data using a linear quadrupole ion trap under various experimental conditions. The instrumental parameters included were (i) the pressure of the collision gas, (ii) the collision energy, (iii) the fill time of the linear ion trap and (iv) the scan rate. The spectral intensity and width of five fragment ions of the doubly charged neuro-active peptide bombesin were used for evaluation, and all experiments were performed so as to resemble the results obtained from a liquid chromatographic peak. The reported results show how fairly simple mathematical tools can be utilized successfully to describe fundamental mechanisms associated with multiple collisional activation and collision-induced dissociation processes without an extensively controlled experimental environment. Most beneficial, using the suggested approach, is the ability to study interaction (synergistic) effects between various parameters. As was realized from the results, many interaction effects are indeed significant. For example, the effect on the signal intensity of different collision gas pressure settings is strongly dependent on the settings of the other parameters. The described approach can easily be adopted for optimization purposes of any MS/MS experiment.     

Investigation into factors affecting precision in ion trap mass spectrometry using different scan directions and axial modulation potential amplitudes

Electrospray ionization mass spectra obtained from different scan directions are observed to be dependent on the axial modulation potential amplitudes used for resonant ejection and on the positive deviation caused by higher even-multipole fields present in most commercial ion traps. The axial modulation voltage influences the dissociation of ions during resonant ejection and the observed mass shifts. The higher even-multipole fields in commercial ion traps are known to influence resonant ejection from the ion trap and can cause a loss in mass resolution for peaks in reverse scan mass spectra compared with that obtained by the forward scan. However, along with the dissociation of ions during resonant ejection causing a loss in resolution, the possibility of resolving an isotopic distribution is also shown to be influenced by the mass shifts caused by the space charge. These mass shifts differ depending on the scan direction employed. A significant loss in resolution can also result from resonant ejection using non-optimal axial modulation voltages. We also present results showing the ejection of ions at betaz = 1/2 using the reverse scan mode without the axial modulation voltage. Ion ejection at betaz = 1/2 is uncommon in commercial (stretched ion traps) with the conventional analytical scan without the use of a frequency of the axial modulation voltage corresponding to this non-linear resonance.     

Characterization of the chemical composition of white chrysanthemum flowers of Hangzhou by using high‐performance ion trap mass spectrometry

In this study, high‐performance liquid chromatography coupled with amaZon SL high‐performance ion trap mass spectrometry was used to analyze the target components in white chrysanthemum flowers of Hangzhou. Twenty‐one components were detected and identified in both white chrysanthemum flowers of Hangzhou samples by using target compound analysis. Furthermore, seven new compounds in white chrysanthemum flowers of Hangzhou were found and identified by analyzing the fragment ion behavior in the mass spectra. The established method can be expedient for the global quality investigation of complex components in herbal medicines and food.     

A comparative study of glycoprotein concentration,glycoform profile and glycosylation site occupancy using isotope labeling and electrospray linear ion trap mass spectrometry

A strategy is presented for comparative analysis of glycoproteins in which the variation of protein concentration, variation of glycosylation site occupancy and variation of glycoform profile can be determined. A comparative study was performed using stable isotope labeling of glycopeptides and peptides by formaldehyde-H₂ and formaldehyde-D₂ and analysis by ESI-MS analysis. The relative intensity of the nonglycosylated peptide provided information about protein concentration variation. Variation of the glycoform profile was obtained by comparing the glycoform profile of d₀- and d₄-dimethyl labeled glycopeptides. By knowing the variation of protein concentration and the variation of glycoform profile, the variation of glycosylation site occupancy could be calculated. The utility of the proposed strategy was demonstrated with ribonuclease B with different protein concentrations, different levels of glycosylation site occupancy and different glycoform profiles.     

Quadrupole ion trap mass spectrometry: a view at the turn of the century

A personal account of the quadrupole ion trap researches carried out in my laboratory and in collaboration with other laboratories. This account commences with the announcement, in 1983, of the first commercially available ion trap detector, manufactured by Finnigan MAT, and continues to the present day. Much of the ion trap mass spectrometry research that took place during the period following this announcement until 1994 has been discussed in detail in three volumes entitled Practical Aspects of Ion Trap Mass Spectrometry that were published in 1995. Except for those researches that impinged directly on our work during this period, no discussion of the contents of these three volumes is repeated here. The ion trap literature from 1994 to the present has been reviewed selectively so as to convey to the reader the dynamic nature of ion trap mass spectrometry and the wide variety of its application.     

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.     

Characterization of in vitro metabolites of trimethoprim and diaveridine in pig liver microsomes by liquid chromatography combined with hybrid ion trap/time-of-flight mass spectrometry

Trimethoprim (TMP) and diaveridine (DVD) are used in combination with sulfonamides and sulfaquinoxlaine as an effective antibacterial agent and antiprotozoal agent, respectively, in humans and animals. To gain a better understanding of the metabolism of TMP and DVD in the food-producing animals, the metabolites incubated with liver microsomes of pigs were analyzed for the first time with high-performance liquid chromatography combined with hybrid ion trap/time-of-flight mass spectrometry. Seven TMP-related and six DVD-related metabolites were characterized based on the accurate MS2 spectra and known structure of the parent drug, respectively. The metabolites of TMP were identified as two O-demethylation metabolites, a di-O-demethylation metabolite, two N-oxides metabolites, a hydroxylated metabolite on the methylene carbon and a hydroxylated metabolite on the methyl group. DVD was also biotransformed to two O-demethylation metabolites, a di-O-demethylation metabolite, an N-oxide metabolite, a hydroxylation metabolite on the methylene carbon and a hydroxylation metabolite followed by O-demethylation. The results indicate that the two compounds have similar biotransformation pathways in pigs. O-Demethylation was the major metabolic route of TMP and DVD in the pig liver microsomes. The proposed metabolic pathways of TMP and DVD in liver microsomes will provide a basis for further studies of the in vivo metabolism of the two drugs in food-producing animals.     

Ion trap mass spectrometry on a comet nucleus: the Ptolemy instrument and the Rosetta space mission

In May 2014, the Rosetta spacecraft is scheduled to rendezvous with the comet Churyumov-Gerasimenko ('67P'). One of the instruments on board the 'Lander' which will descend on to the surface of the comet is a miniaturised GC/MS system that incorporates an ion trap mass spectrometer, specially developed for isotope ratio analysis. This article describes the development and optimisation of the ion trap for this unique application, and presents a summary of the range of pre-programmed experiments that will contribute to the characterisation of the solid and volatile cometary materials.     

Triterpenoid saponins profiling by adducts-targeted neutral loss triggered enhanced resolution and product ion scanning using triple quadrupole linear ion trap mass spectrometry

Triterpenoid saponins (TSs) are a unique class of high molecular weight glycosides and have been frequently used in cosmetic and phytotherapy industry. There is a great need to comprehensively profile these plant metabolites for studying their functions. In the present study, a novel adducts targeted neutral loss (NL), triggered enhanced resolution (ER) and enhanced product ion (EPI) scanning approach were described for TSs profiling using a triple quadrupole linear ion trap mass spectrometry. This approach circumvented the disadvantages of poor glycosidic bond cleavage of TSs by monitoring the NH₃ (NL17) and HCOOH (NL46) loss of their abundant ammonium and formate adducts, respectively. The sugar-loss independent NL scanning served as a sensitive survey scan and triggered information-dependent ER and EPI scans to increase peak assignment confidence. NL17 was superior to NL46 for TSs characterization due to the better fragmentation of ammonium adducts than formate adducts. For those TSs undetectable by NL17, precursor ion (PI) scan for sapogenin fragments could be used to screen out non-adducted TSs. The NL/PI-ER-EPI approach was applied for TSs profiling in Astragali Radix, a famous medicinal and nutritional plant widely used in Asian countries and United States. In total, 136 TSs were detected while previous research using high resolution mass spectrometry based full scan only detected 22 TSs in this herb.     

Evidence for linkage position determination in known feruloylated mono- and disaccharides using electrospray ion trap mass spectrometry

Various feruloylated arabinose- and galactose-containing mono- and disaccharides with known linkage configurations (2-O-(trans-feruloyl)-L-arabinopyranose, 5-O-(trans-feruloyl)-L-arabinofuranose, O-[2-O-(trans-feruloyl)-alpha-L-arabinofuranosyl]-(1-->5)-L-arabinofuranose, and O-[6-O-(trans-feruloyl)-beta-D-galactopyranosyl]-(1-->4)-D-galactopyranose) were analyzed by electrospray ionization mass spectrometry using an ion trap or a quadrupole time-of-flight (Q-TOF) mass analyzer. Collision-induced dissociation (CID) experiments using the two mass analyzers generated similar tandem mass spectrometric (MS/MS) fragmentation patterns. However, the ester-bond cleavage ions were more abundant using the Q-TOF mass analyzer. Compared with the positive ion mode, the negative ion mode produces simpler and more useful CID product-ion patterns. For arabinose-containing feruloylated compounds, results obtained with both analyzers show that it is possible to assign the location of the feruloyl group to the O-2 or O-5 of arabinosyl residues. In the characterization of the 2-O-feruloyl and 5-O-feruloyl linkages, the relative abundance of the cross-ring fragment ions at m/z 265 (-60 u or -62 u after 18O-labelling) and at m/z 217 (-108 u or -110 u after 18O-labelling) play a relevant role. For galactose-containing feruloylated compounds, losses of 60, 90 and 120 Da observed in MS3 experiment correspond to the production of 0,2A1, 0,3A1 and (0,2A1-60 Da) cross-ring cleavage ions, respectively, fixing the location of feruloyl group at the O-6 of the galactose residue.     

Determination of regioselectivity in ring opening of tert-butylaziridinones by a combination of (15)N labeling and electrospray ionization-ion trap mass spectrometry

The ring opening of 1,3-di-tert-butylaziridinone by tert-butylamine and aniline was investigated by using electrospray ionization and collision-induced dissociation in an ion trap mass spectrometer in conjunction with (15)N labeling of the two amine nucleophiles. Using the MS(n) capabilities of the ion trap instrument, we were able to monitor the retention of the (15)N label through successive fragmentation steps. Both amines exhibited a remarkable degree of selectivity in that they both cleaved exclusively the 1,3-bond (the alkyl-nitrogen bond). This result is in contrast to that obtained previously with methylamine, which cleaved just the opposite bond, namely, the 1,2-bond (the acyl-nitrogen bond). These contrasting results could not have been predicted by previously published guidelines.     

q value and parent energy optimization using a low-voltage ionization approach increases resolution in linear ion trap mass spectrometry

In this work, the isolation step in the linear ion trap was performed using different “q values” conditions at a low collision-induced dissociation (CID) energy leading to the parent ion resolution improvements, reasonably due to better ion energy distribution. According to the results, we obtained a greater resolution and mass accuracy operating in both traditional electrospray and low voltage ionization near the q value = 0.778 and with a CID energy of 10%. This effect was evaluated with low-molecular-mass compounds (skatole and arginine). The proposed optimization yielded a superior instrument performance without adding technological complexity to mass spectrometry analyses.