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Methotrexate (MTX) is a therapeutic drug that is widely used in clinic for treatment of a variety of cancers. However, MTX has limited selectivity and serious cytotoxicity, at the same time, there are problems such as narrow therapeutic window and large individual variability in metabolism and excretion of MTX. Therefore, blood concentration monitoring is required for MTX administration in clinical practice. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) has the advantages of strong specificity, good separation characteristics, high sensitivity and fast detection speed, which has become the internationally recognized “gold standard” for blood concentration monitoring of drugs. In this study, an isotope dilution mass spectrometry method was developed for accurate measurement of MTX in serum by the house-made QLIT-6610MD quadrupole-linear ion trap liquid chromatography-mass spectrometer. Unlike the traditional triple quadrupole QqQ tandem mass spectrometer, the quadrupole-linear ion trap (Q-LIT) mass spectrometer adopts the quadrupole-linear ion trap direct axial coupling design, i.e., a single linear ion trap is used to replace the QqQ tandem mass spectrometer’s back-end fragmentation cell and the quadrupole, and no other components are installed between the quadrupole and linear ion trap, which greatly streamlines the quality and efficiency of the mass spectrometer while ensuring the original performance of the instrument. With this unique configuration, the QLIT-6610MD instrument uses a simultaneous fragmentation and accumulation technique, which remarkedly reduces matrix-induced interferences and effectively reduces space charge effects. Serum samples were pretreated with methanol to precipitate proteins and the supernatants were measured by QLIT-6610MD spectrometer. The linear correlation coefficient (R2＞0.999 0) is obtained for MTX in the range of 10-5 000 μg/L. The limit of quantification is 10 μg/L. The precision of the quality control is better than 6.94%, and the recoveries of spiked serum samples are 86.39%-97.84% with a coefficient of variation less than 8.04%. We used the QLIT-6610MD and AB QTRAP 6500+ liquid chromatography-mass spectrometers to analyze 70 clinical serum samples for comparison of the performance of the house-made instrument by means of Pearson’s coefficient and BLand-ALtman method. The results showed that the QLIT-6610MD mass spectrometry achieves a similar level of performance to AB ATRAP 6500+ instrument, and provides a new domestic instrument option for clinical mass spectrometry. In addition, this study explores the possibility applying the multi-stage fragmentation technique (MSn) to determine MTX in serum, gaining fundamental data for future studies.

Methotrexate (MTX) is a therapeutic drug that is widely used in clinic for treatment of a variety of cancers. However, MTX has limited selectivity and serious cytotoxicity, at the same time, there are problems such as narrow therapeutic window and large individual variability in metabolism and excretion of MTX. Therefore, blood concentration monitoring is required for MTX administration in clinical practice. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) has the advantages of strong specificity, good separation characteristics, high sensitivity and fast detection peed, which has become the internationally recognized “ gold standard” for blood concentration monitoring of drugs. In this study, an isotope dilution mass spectrometry method was developed for accurate measurement of MTX in serum by the house-made QLIT-6610MD quadrupole-linear ion trap liquid chromatography-mass spectrometer. Unlike the traditional triple quadrupole QqQ tandem mass spectrometer, the quadrupole-linear ion trap (Q-LIT) mass spectrometer adopts the quadrupolelinear ion trap direct axial coupling design, i.e., a single linear ion trap is used to replace the QqQ tandem mass spectrometer’s back-end fragmentation cell and the quadrupole, and no other components are installed between the quadrupole and linear ion trap, which greatly streamlines the quality and efficiency of the mass spectrometer while ensuring the original performance of the instrument. With this unique configuration, the QLIT-6610MD instrument uses a simultaneous fragmentation and accumulation technique, which remarkedly reduces matrix-induced interferences and effectively reduces space charge effects. Serum samples were pretreated with methanol to precipitate proteins and the supernatants were measured by QLIT-6610MD spectrometer. The linear correlation coefficient (R²>0.999 0) is obtained for MTX in the range of 10-5 000 μg/L. The limit of quantification is 10 μg/L. The precision of the quality control is better than 6.94%, and the recoveries of spiked serum samples are 86.39%-97.84% with a coefficient of variation less than 8.04%. We used the QLIT-6610MD and AB QTRAP 6500+ liquid chromatography-mass spectrometers to analyze 70 clinical serum samples for comparison of the performance of the house-made instrument by means of Pearson’s coefficient and BLand-ALtman method. The results showed that the QLIT-6610MD mass spectrometry achieves a similar level of performance to AB ATRAP 6500+ instrument, and provides a new domestic instrument option for clinical mass spectrometry. In addition, this study explores the possibility applying the multi-stage fragmentation technique (MSn) to determine MTX in serum, gaining fundamental data for future studies. [ABSTRACT FROM AUTHOR]

Rapid and accurate on-site detection of chemical warfare agents (CWAs) could defend military and civilian populations against current and emerging chemical weapons. With the development of ambient ionization and linear ion trap technology, the rapid and accurate quantitative determination method of CWAs based on direct ionization and multistage mass spectrometry has attracted widespread attention. In this study, a microliter electrospray ionization-miniature linear ion trap mass spectrometry (LIT-MS) instrument was designed and constructed, and the effects of quadrupole enhanced dipole resonance excitation on the resolution and sensitivity were investigated; consequently, the parameters of CWAs detection were optimized. Based on the broad time-frequency ion excitation technology, accurate multiple reaction monitoring (MRM) quantitative analysis of DMMP (G-series agent simulants, m/z 125 → m/z 93) was obtained. The linear correlation coefficient in the concentration range of 1 to 20 μg/mL could reach 99.02%, and the relative standard deviations (RSD) of continuous repeatability, interday repeatability, and intraday repeatability were all less than 10%. The results showed that the accurate pseudo-MRM detection method based on miniature linear ion trap mass spectrometry for CWAs detection was feasible. [ABSTRACT FROM AUTHOR]

We explore the spatial distribution of ions in a linear multipole radio-frequency ion trap by ion-trajectory simulation using the SIMION software. As a typical example, a two-dimensional column density is characterised for Ag2+ ions stored in several types of the trap. Taking into account the effects of the space charge and ion–buffer He collisions, we are able to reproduce a ring profile of an ion distribution experimentally observed for a linear octopole trap at a high density of ions close to the space-charge limit. This simulation demonstrates also that the profile of the ion distribution is dependent on the number of ions stored and the temperature of a buffer He gas. As for a quadrupole trap, an ion distribution is shown to be located around the central axis of the trap as observed by experiment. An influence of the electrode structure is also discussed for the quadrupole trap. [ABSTRACT FROM AUTHOR]

The demand for accurate mass spectrometry measurement in the field of clinical diagnosis is increasing. In the face of foreign monopoly, our team has developed new technologies and new methods for the selective enrichment of trace targets in complex matrices by ion traps, and has developed a quadrupole-linear ion trap (quadrupole-linear ion trap, Q-LIT) tandem mass spectrometer with independent intellectual property rights and a liquid chromatography tandem mass spectrometry system (model QLIT-6610MD), which have obtained a medical device registration certificate in China. In this study, a home-built Q-LIT liquid chromatography-tandem mass spectrometer QLIT-6610MD was developed to measure vancomycin in serum with high accuracy . After protein precipitation and liquid-liquid extraction, the samples were analyzed by QLIT-6610MD. The endogenous substances in the samples did not interfere with the quantification. The results showed that vancomycin has a good linear relationship of signal intensity vs. concentration in the range of 1.56-50.0 mg/L with the linear correlation coefficient (R2)≥0.99, and the limit of detection and limit of quantitation are 0.19 and 1.56 mg/L, respectively. Intra-day and inter-day precisions are 1.62%-3.82% and 2.07%-5.07%, respectively. The recoveries of vancomycin in serum samples are 95.97%-97.74%. The coefficient of variability (CV) of matrix effect normalization factor is less than 7.60%, CV of sample stability is better than 4.26%, and CV of long interval sample analysis is better than 2.13%. The method was verified by the determination of low, medium and high quality controls, and the results were all within the range of target values. QLIT-6610MD, AB API4000 and YS EXACT 9900MD were used to determine 42 real clinical serum samples. The correlation and consistency of the data were analyzed by Deming regression, Bland-Altman analysis and Pearson correlation analysis. The results showed good consistency among the results obtained by the three spectrometers, indicating that the data of three instruments are comparable, which prove that the home-made QLIT-6610MD can reach the quantitative accuracy of triple quadrupole-mass spectrometer. The instrument can effectively reduce the interference of matrix ions and enhance the capture efficiency of target ions, based on quadrupole-linear ion trap tandem mass spectrometric technique. QLIT-6610MD has great potential to provide a new instrumentation solution for real-time clinical analysis in the future.

In order to ensure the measurement accuracy of ion trap mass spectrometer, it is necessary to perform mass calibration on the instrument when there is a mass shift. Mass calibration can be achieved by improving the stability of the electrical components or upgrading the hardware with significant technical costs. Compared with hardware optimization. mass calibration based on software algorithms can better utilize the performance of existing instruments. Mass calibration can be achieved by manually inputting standard samples or calibration solution parameters. However, mass axis calibration in this way still requires setting specific segmentation points based on the actual situation and manually adjusting them to achieve the desired accuracy. Therefore, to improve the low efficiency with manual segmentation during mass calibration, an automatic segmented calibration algorithm was proposed to improve the calibration accuracy and facilitate rapid operation. The algorithm used point by point fitting to deter- mine whether the segment interval met the requirements and also determined each segment interval. At the same time, the mass axis was automatically segmented to reduce the mass deviation of each checkpoint. This method was compared with traditional method, different deviation thresholds were explored, and multiple instruments were selected to verify this method. The results showed that the algorithm can reasonably segment the mass axis and establish a new linear relationship between electrical parameters and m/z under existing conditions, allowing the deviation of each checkpoint to be controlled within a lower preset range (±0.1 u), thus improving the instrument's calibration efficiency and measurement accuracy. reducing the difficulty of personnel operation. The significance of this study is that the algorithm only adjusts and optimizes the signals generated by the hardware without changing the structure of the instrument itself, which is helpful for improving the overall performance and stability of the instrument. Moreover, the principle and conclusion of the algorithm are independent of the experimental platform. so it can be applied to a variety of other types of mass spectrometers. For the insufficient points. firstly, the upper limit of accuracy provided by the algorithm itself is still determined by the hardware accuracy of the instrument, so it is only possible to calibrate and optimize the mass axis within a certain accuracy range. Secondly, because the calibration process requires a certain number of reference points. which poses certain requirements for the selection of calibration solutions. [ABSTRACT FROM AUTHOR]

Accurate and highly sensitive analysis of folpet and captan was accomplished using liquid chromatography-triple quadrupole linear ion trap mass spectrometry (LC-QqQIT) with selective ion mode; mass filtering, collision, and trapping condition. Dimensional mass spectrometry (MS3) parameters were optimized for the residue detection of folpet and captan in six food commodities (apples, tomatoes, sweet pepper, wheat flour, sesame seeds, and fennel seeds). The sample preparation method was based on the known QuEChERS protocol, except a mixture of acetonitrile/acetone was used for the sample extraction from the sesame seeds. The robustness and reliability of the developed MS3 method were demonstrated by performing a full validation, according to SANTE/11312/2021, at 0.01–0.25 mg/kg. Recovery ranged from 83 to 118% with a relative standard deviation below 19% in all the tested commodities, and limits of quantifications (LOQs) were 0.01 mg/kg in apples and tomatoes; 0.03 mg/kg in sweet pepper; and 0.05 mg/kg in wheat flour, sesame seeds, and fennel seeds. Monitoring results showed that about 90% of apples contained captan residue, and in sweet pepper, concentrations of captan and folpet as high as 1.57 and 0.97 mg/kg were found, respectively. The novel developed MS3 method enabled more reliable identification of these commonly problematic fungicides at lower LOQs than previously reported methods. [ABSTRACT FROM AUTHOR]

Vitamin D deficiency and insufficiency is a global health issue that afflicts people of different age groups all over the world. As a reliable indicator for the evaluation of vitamin D, 25OHD is usually determined by LC-MS/MS. The tandem mass spectrometry based on ion trap has the characteristics of simple structure and high sensitivity. However, there are some problems such as narrow linear range and space charge effect, which limit its analysis of trace substances in complex matrix samples. In this study, the device and technology of a new quadrupole linear ion trap mass spectrometry was used to reduce the space charge interference of trace or ultra trace target ions by high abundance impurity ions in complex matrices. For the first time, isotope dilution mass spectrometry for accurate measurement of serum 25OHD was established by QLIT-6610MD, which is quadrupole-linear ion trap tandem mass spectrometer, and was independently developed by Technology Innovation Center of Mass Spectrometry for State Market Regulation, Center for Advanced Measurement Science, National Institute of Metrology. Serum samples were precipitated with methanol, extracted with n-hexane, dried with liquid nitrogen, redissolved in the initial mobile phase, and determined by QLIT-6610MD. The matrix-matched standard curve was used for quantification. The linear ranges of 25OHD2 and 25OHD3 were in the range of 0.78-50 μg/L and 1.56-100 μg/L with R2>0.999 9, respectively. The detection and quantification limits of 25OHD2 and 25OHD3 were 0.06, 0.12 μg/L and 0.02, 0.06 μg/L, respectively. The precision of quality control was better than 4.06%. The recoveries ranged from 99.25% to 108.38%, and the coefficients of variation were all less than 5.1%. After the method confirmation, the quantitative results of clinical samples were compared with triple quadrupole tandem mass spectrometry. 50 Clinical serum samples were measured and compared by QLIT-6610MD, AB 4500MD and YS EXACT 9900MD. The correlation and consistency of the data were analyzed by Pearson and Bland-Altman. The correlation coefficient of the three groups data was R≥0.998 0, P

Vitamin D deficiency and insufficiency is a global health issue that afflicts people of different age groups all over the world. As a reliable indicator for the evaluation of vitamin D, 25OHD is usually determined by LC-MS/MS. The tandem mass spectrometry based on ion trap has the characteristics of simple structure and high sensitivity. However, there are some problems such as narrow linear range and space charge effect, which limit its analysis of trace substances in complex matrix samples. In this study, the device and technology of a new quadrupole linear ion trap mass spectrometry was used to reduce the space charge interference of trace or ultra trace target ions by high abundance impurity ions in complex matrices. For the first time, isotope dilution mass spectrometry for accurate measurement of serum 25OHD was established by QLIT-6610 MD, which is quadrupole-linear ion trap tandem mass spectrometer, and was independently developed by Technology Innovation Center of Mass Spectrometry for State Market Regulation, Center for Advanced Measurement Science, National Institute of Metrology. Serum samples were precipitated with methanol, extracted with n-hexane, dried with liquid nitrogen, redissolved in the initial mobile phase, and determined by QLIT-6610 MD. The matrix-matched standard curve was used for quantification. The linear ranges of 25OHD2 and 25OHD3 were in the range of 0.78-50 μg/L and 1.56-100 μg/L with R²＞0.999 9, respectively. The detection and quantification limits of 25OHD2 and 25OHD3 were 0.06, 0.12 μg/L and 0.02, 0.06 μg/L, respectively. The precision of quality control was better than 4.06%. The recoveries ranged from 99.25% to 108.38%, and the coefficients of variation were all less than 5.1%. After the method confirmation, the quantitative results of clinical samples were compared with triple quadrupole tandem mass spectrometry. 50 Clinical serum samples were measured and compared by QLIT-6610 MD, AB 4500 MD and YS EXACT 9900 MD. The correlation and consistency of the data were analyzed by Pearson and Bland-Altman. The correlation coefficient of the three groups data was R≥0.998 0, P＜0.01, and the results of Bland-Altman analysis showed good consistency, indicating that the results measured by the three instruments were consistent, which meant that QLIT-6610 MD can meet the needs of clinical diagnosis. QLIT-6610 MD achieved the same level of triple quadrupole mass spectrometry to determine the concentration of 25OHD in serum. It can not only become a new choice for clinical mass spectrometry, but also lay a foundation for the development of domestic mass spectrometer. Based on the direct axial coupling technology of quadrupole and linear ion trap, QLIT-6610 MD can greatly reduce the interference of matrix ions and make the ion trap detect target ions more effectively. This technology has a strong potential to further improve the measurement accuracy of trace or ultra trace targets in complex matrices. In the future, it can be applied to mass spectrometry monitoring scenarios that needs to meet the requirements of high accuracy, high sensitivity, on-site speed and low cost at the same time. [ABSTRACT FROM AUTHOR]

Ion trajectory numerical simulation is used to find the linear ion trap excitation contour in the second stability region. The effects of initial conditions, the ejection Mathieu parameter, scan speed, dipole excitation voltage and gas damping are studied. Modeling shows that in the stability region center the resolution power is ≈200000 (at full width half height of a peak, FWHM) at pressure 0.1 mTorr and 100 % excitation efficiency (not taking into account the space charge).

The miniaturization of ion trap mass analyzers is an important direction in the development of mass spectrometers. In this work, we proposed two models of miniaturized HreLIT with a field radius of about 2 mm based on the existing research on conventional HreLIT and other ion traps, one with ions ejection slits on one pair of electrodes only (2-slit model) and the other with the same slits on all electrodes (4-slit model). The relationship of mass resolution with r/rx and the "stretch" distance of electrodes in the ejection direction is investigated by theoretical simulations. Trends of electric fields inside the ion traps were discussed as well. The comparable maximum resolution is observed at r/rx = 2/1.4 in both models, but stretching simulations revealed that the peak resolution of the 2-slit model was higher than that of the other model by about 8%. The highest value of 517 was obtained when stretching 1.1 mm. Furthermore, the resolution of ions with m/z = 119 could exceed 1000 when the scan rate was reduced to 800 Th/s. The mass spectrometry capability of miniature HreLIT has been confirmed theoretically, and it laid the foundation for the subsequent fabrication with MEMS technology. [ABSTRACT FROM AUTHOR]

Targeted mass spectrometry (MS) methods are powerful tools for the selective and sensitive analysis of peptides identified in global discovery experiments. Selected reaction monitoring (SRM) is the most widely accepted clinical MS method due to its reliability and performance. However, SRM and parallel reaction monitoring (PRM) are limited in throughput and are typically used for assays with around 100 targets or fewer. Here we introduce a new MS platform featuring a quadrupole mass filter, collision cell, and linear ion trap architecture, capable of targeting 5000-8000 peptides per hour. This high multiplexing capability is facilitated by acquisition rates of 70-100 Hz and real-time chromatogram alignment. We present a Skyline external software tool for building targeted methods based on data-independent acquisition chromatogram libraries or unscheduled analysis of heavy labeled standards. Our platform demonstrates ∼10× lower limits of quantitation (LOQs) than traditional SRM on a triple quadrupole instrument for highly multiplexed assays, due to parallel product ion accumulation. Finally, we explore how analytical figures of merit vary with method duration and the number of analytes, providing insights into optimizing assay performance.

Hepatitis C virus (HCV) is an infectious disease that has become a global clinical issue because of its significant morbidity and mortality. Novel anti‐hepatitis C drugs are continuously developed to decrease the pervasiveness of the infection globally. A synthetic ravidasvir, benzimidazole‐naphthylene‐imidazole derivatives, has been used as an anti‐HCV drug. This study determined the metabolites of ravidasvir and its pharmacokinetics in rats using information‐dependent acquisition and multiple reaction monitoring scanning modes in linear ion trap LC–MS/MS instrument, respectively. Two time‐programming linear‐gradient chromatographic methods were employed using a Kinetex C18 column (50 × 3 mm, 2.6 μm) and a Luna HILIC column (100 × 4.6 mm, 3 μm) for the qualitative and quantitative determination of ravidasvir and its metabolites, respectively. In silico prediction where sites in a molecule are susceptible to metabolism by cytochrome P450 was implemented, which helped in proposing the metabolic pathway of ravidasvir. The most dominant metabolite in rat liver microsomal samples was oxidative ravidasvir, where one O‐demethylated metabolite and eight isomers of the oxidative ravidasvir metabolites were identified. The study provides essential data for proposing the metabolic pathway and successfully applied it to determine the pharmacokinetics of ravidasvir in rat plasma. [ABSTRACT FROM AUTHOR]

The miniaturization of ion trap mass analyzers is an important direction in the development of mass spectrometers. In this work, we proposed two models of miniaturized HreLIT with a field radius of about 2 mm based on the existing research on conventional HreLIT and other ion traps, one with ions ejection slits on one pair of electrodes only (2-slit model) and the other with the same slits on all electrodes (4-slit model). The relationship of mass resolution with r/rx and the “stretch” distance of electrodes in the ejection direction is investigated by theoretical simulations. Trends of electric fields inside the ion traps were discussed as well. The comparable maximum resolution is observed at r/rx = 2/1.4 in both models, but stretching simulations revealed that the peak resolution of the 2-slit model was higher than that of the other model by about 8%. The highest value of 517 was obtained when stretching 1.1 mm. Furthermore, the resolution of ions with m/z = 119 could exceed 1000 when the scan rate was reduced to 800 Th/s. The mass spectrometry capability of miniature HreLIT has been confirmed theoretically, and it laid the foundation for the subsequent fabrication with MEMS technology.

Linear ion traps and quadrupole mass spectrometers play vital roles in quantum technologies and classical mass spectrometry respectively. Therefore, such systems with nearly same operational principles, are very well studied both theoretically and experimentally. Despite such vast knowledge base, linear ion traps continue to be an important research topic, particularly the effect of small perturbations from ideal conditions. Here, non-degenerate nonlinear resonances of the ion dynamics in a linear three-segmented round-rod radio-frequency ion trap have been studied. Purposefully designed perturbation from an ideal 4-rod symmetric structure results in additional instabilities in the dynamics of the trapped ions. The weightage of the dodecapole potential increases by an order of magnitude in such an asymmetric setup compared to that present in usual symmetric setup of nearly equivalent geometry. The experimental results are corroborated by ion dynamics simulations with commercial software SIMION. Increased dodecapole potential in the asymmetric structure leads to resolution of the frequency of ion oscillation in two mutually perpendicular directions in the radial plane which is otherwise unresolved in a symmetric structure in absence of dc potential. Such asymmetric linear trap, in principle, finds importance in the study of Coulomb crystal, mass spectrometry and relevant trapped ion dynamics. It also opens up the possibility to remove undesired ion species (often known as dark ion) within a chain of physical qubits. • One middle electrode in a three-segmented linear ion trap is taken of different diameter making the trap setup asymmetric. • Nonlinear resonances appear as non-degenerate in the rf stability diagram. • Weightage of the dodecapole potential is larger by an order of magnitude compared to symmetric setup of equivalent geometry. • Increased dodecapole potential has promising applications in mass spectrometry, dark ion elimination from trapped ion-chain. [ABSTRACT FROM AUTHOR]

The detection of volatile organic compounds (VOCs) in water faces challenges due to the presence of complex matrix interferences and low concentration. This paper presented a portable gas chromatography linear ion trap mass spectrometer (GC-LIT-MS) coupled with dynamic headspace sampling (DHS) system for sensitive and rapid on-site analysis of VOCs in water. The instrument weighs 18 kg and has compact dimensions of 43 cm × 35 cm x 20 cm, offering portability and convenience. A low thermal mass (LTM) chromatographic column, utilizing resistive heating, enables rapid heating and cooling within the runtime of GC. The linear ion trap, for the first time, has been integrated as a mass analyser in portable gas chromatography-mass spectrometer (GC-MS). Its ability to store a greater number of ions within the trap expands the dynamic range of the instrument. The influence of dynamic headspace injection conditions on the purging efficiency of VOCs was investigated and the equilibrium temperature was optimized. The GC-LIT-MS method was demonstrated to be capable to identify and separate 55 VOCs in water within 4 min, with most of them exhibiting detection limits of less than 1 μg L−1. The calibration of 4 VOCs with concentrations ranged from 2 parts per million (ppm) to 200 ppm showed excellent linearity (R2 > 0.99) and dynamic range more than five orders of magnitude. Resolution superior to unit mass was achieved within the range of 15 AMU to 550 AMU. [Display omitted] • A portable gas chromatography linear ion trap mass spectrometer was developed. • The great ion storage capacity of the linear ion trap extends the dynamic range of the instrument. • Coupled with dynamic headspace sampling, the GC-LIT-MS was capable to identify and separate 55 VOCs in water within 4 min, exhibiting excellent performances. [ABSTRACT FROM AUTHOR]

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Based on reviewing the structure and principle of the quadrupole linear ion trap, this review explains the core technical principles of the linear ion trap electronic system and cascade mass spectrometry, and introduces the stored waveform inverse Fourier transform technique in quadrupole linear ions. The application in the well, especially how to select the parent ion. The quadrupole linear ion trap is a magical analyzer that analyzes ions with a mass-to-charge ratio of thousands or more. In the full scan mode, the ion trap still has high sensitivity, and its sensitivity is often 10-1 000 times higher than that of the quadrupole. Compared to other types of analyzers, MSn of multi-stage tandem mass spectrometry can be achieved with a single linear ion trap, which is very useful for structural identification of analytes. The resonance-assisted alternating voltage is used to excite the parent ion and the fragment ion, which is the key to achieving cascade mass spectrometry. In addition, the quadrupole linear ion trap is relatively easy to manufacture, requires low processing accuracy, and is cost effective. This review will introduce the mechanical structure of the quadrupole linear ion trap and the technical principles of circuit implementation; describe how to apply collision induced dissociation and assisted RF to achieve linear ion trap tandem mass spectrometry; explain how to pass RF voltage and DC voltage in a linear ion trap. The cooperation is to capture and excite ions; finally, the practical application of the stored waveform inverse Fourier transform technique in selecting parent ions and separating adjacent mass ions is also demonstrated. [ABSTRACT FROM AUTHOR]

In the development of commercial quadrupole mass spectrometers, there is an interest in improving the performance characteristics such as transmission, resolution, and mass range. In particular, parametric and dipolar resonance excitation of trapping ions are used for linear quadrupole mass filters. Theoretical methods and numerical simulation of ion trajectories were applied for study of ion-optical properties. The review is devoted to description of different excitation methods to improve QMF performance and consists of three parts. The first part presents the results of a linear ion trap simulation for various operating conditions and excitation methods. The second part considers the effects of dipole excitation (DE) on the performance of the quadrupole mass filter. The last part analyzes the formation of stability islands by different methods of quadrupole excitation. To date conditions of mass separation in quadrupole mass filters with sin wave supply were described for stability islands of the first and third stability regions formed by quadrupole and DE. By complicating the electronics such methods allow to overcome the destructive influence of electric field distortions and obtain a resolving power and ion transmission efficiency comparable with commercial devices. At quadrupole resonance excitation by a two-frequency signal, it is possible to reduce the length of electrodes three times without losses in resolution and transmission, which reduces the cost of rod set production with micrometer accuracy. Dipole resonance excitation allows controlling the shape of the mass peak by changing amplitude and phase of the auxiliary AC signal. The main factors affecting the resolving power of a linear ion trap are described theoretically. The numerical modeling results are confirmed by experiment., Competing Interests: Declaration of conflicting interestsThe author declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Atoms and molecules often react at different rates depending on their internal quantum states. Thus, controlling which internal states are populated can be used to manipulate the reactivity and can lead to a more detailed understanding of reaction mechanisms. We demonstrate this control of reactions by studying the electronically excited state reaction. This reaction is exothermic only if Ca is in one of its excited electronic states. Using laser-cooling and electrodynamic trapping, we cool and trap Ca at millikelvin temperatures for several minutes. We can then change the fraction of time they spend in each of the two excited states by adjusting the detunings of the cooling lasers. This allows us to disentangle the reactions that begin with Ca in the 2P -state from the ones where Ca is in the 2D -state. Using time-of-flight mass spectrometry, we determine independent reaction rate constants for Ca in both electronically excited states. [ABSTRACT FROM AUTHOR]

We report automated procedures for multiple tandem mass spectra acquisition allowing UV–Vis photodissociation action spectroscopy measurements of ions and radicals. The procedures were developed for two commercial ion trap mass spectrometers and applied to collision-induced and electron–transfer dissociation tandem mass spectrometry modes of ion generation. [ABSTRACT FROM AUTHOR]

We report here a novel approach for the extraction and analysis of thyroid hormones (TH) and their metabolites (THM) from human serum samples. Our method features a compact, 96-well micro-titre plate-based pre-analytic extraction/clean-up workflow combined with an isotope dilution LC-MS/MS-MS3 analytical method. In particular, these features make possible the detection of iodothyronines at their endogenous concentrations in serum differing by a factor of ca. 104, with potential to semi-automate the pre-analytics. The method was validated by the assessment of linearity, lower limits of quantification and detection (LLOQ and LLOD respectively), intra- and inter-day accuracy, precision, process efficiency (PE), matrix effect (ME) and relative recovery (RE). Calibration curves were linear in the concentration range in sample matrix from 0.1–250 nM for T3, rT3, T4 and 3-T1AM and from 0.005–1 nM for 3,5-T2 and 3,3′-T2. Using a 200-μL sample volume, the analyte dependant LLOQ were in the range 0.005 (3,5-T2) to 0.25 (T4) nM and LLOD were between 0.002 (3,5-T2) and 0.052 nM (T4). We applied the LC-MS/MS-MS3 method to the analysis of a cross section of patients with disorders of the thyroid hormone axis. T4, T3 and rT3 concentrations (± standard deviation) were 120 ± 18, 1.9 ± 0.4 and 0.45 ± 0.09 nM respectively. 3,3′-T2 concentrations (± standard deviation) were 0.079 ± 0.022 nM; 3,5-T2 concentrations were below the LLOQ and/or LLOD in all but a single sample (0.013 nM). This method expands the analytical spectrum to endogenous thyroid hormone metabolites such as 3,5-T2 which exert biological actions and rT3 which may act as surrogate markers for disturbed thyroid hormone metabolism. [ABSTRACT FROM AUTHOR]

We have demonstrated the use of a simple single ion trap mass spectrometer to identify classes of compounds as well as individual components in complex mixtures. First, a neutral reagent was used to mass tag oxygen-containing analytes using a gas-phase ion/molecule reaction. Then, a neutral loss scan was used to indicate the carboxylic acids. The lack of unit mass selectivity in the neutral loss scan required subsequent product ion scans to confirm the presence and identity of the individual carboxylic acids. The neutral loss scan technique reduced the number of data-dependent MS/MS scans required to confirm identification of signals as protonated carboxylic acids. The method was demonstrated on neat mixtures of standard carboxylic acids as well as on solutions of relevant pharmaceutical tablets and may be generalizable to other ion/molecule reactions. [ABSTRACT FROM AUTHOR]

MS/MS spectrum matching currently serves as a favored means to identify the concerned metabolites attributing to the accessibility of several famous databases. However, the rule that takes the entire structure into account frequently leads to "0 hit" when inquiring MS/MS (usually MS2) spectrum in the databases. Conjugation plays an important role for the high-level structural diversity of metabolites in all organisms, and a given conjugate usually consists of two or more substructures. If MS3 spectra participate in database retrieval, the structural annotation potential of those databases should be dramatically expanded via identifying substructures. Attributing to the ubiquitous distribution pattern, flavonoid glycosides were deployed as the representative family to justify whether the primary fragment ion termed as Y 0 +, resulted from neutral loss of glycosyl residue(s), generated identical MS3 spectrum with MS2 spectrum of the aglycone cation namely [A+H]+. Because of owning unique ability to measure MS/MS spectrum with the exactly desired exciting energy, linear ion trap chamber of Qtrap-MS was responsible for generating the desired MS3 and MS2 spectra. When taking both m/z and ion intensity features into consideration, the findings included: 1) glycosides sharing identical aglycones produced the same MS3 spectra for Y 0 +; 2) different MS3 spectra for Y 0 + occurred amongst glycosides bearing distinct, even isomeric, aglycones; 3) isomeric aglycones generated different MS2 spectra; and 4) MS3 spectra for Y 0 + agreed with MS2 spectra of [A+H]+ when comparing paired glycoside and aglycone. Together, fingerprint comparison between MS3 and MS2 spectra could structurally annotate the substructures and further advance MS/MS spectrum matching towards the identification of, but not limited to, aglycones for flavonoid glycosides. [Display omitted] • Fingerprint comparison between MS3 and MS2 spectra advance MS/MS spectrum matching. • The MS3 spectrum of Y 0 + was well-aligned with the MS2 spectrum of [A+H]+. • Forty-eight authentic flavonoids including glycosides and aglycones were used. • Spectrum matching helps the annotation of substructures for numerous metabolites. [ABSTRACT FROM AUTHOR]

We report on the performance of a cryogenic 2D linear ion trap (cryoLIT) that is shown to be mass-selective in the temperature range of 17-295 K. As the cryoLIT is cooled, the ejection voltages during the mass instability scan decrease, which results in an effective mass shift to lower m/z relative to room temperature. This is attributed to a decrease in trap radius caused by thermal contraction. Additionally, the cryoLIT generates reproducible mass spectra from day-to-day, and is capable of performing stored waveform inverse Fourier transform (SWIFT) mass isolation of fragile N2-tagged ions for the purpose of background-free infrared dissociation spectroscopy.ᅟ [ABSTRACT FROM AUTHOR]

Liquid chromatography coupled with tandem mass spectrometry has long been employed for the quantitation of molecules. With judicious selection of precursor and fragment ions, multiple-reaction monitoring assays can be developed rapidly for these experiments. However, there are cases where analyses struggle due to high background signals caused by matrix effects that interfere with the analytical signal. An alternative to MRMs involves using two stages of tandem mass spectrometry - an MS3 experiment. Although this technique can provide greater selectivity than MS/MS experiments, cycle times for MS3 experiments are typically longer than MRM-type experiments. Here, we present a quantitation technique employing an MS3 method with shorter cycle times than traditional linear ion trap MS3 scans. Termed 'scan-free' MS3, this technique performs 'mass analysis' by isolating the ions of interest in the linear ion trap and then emptying the trap of these ions. The signal will be due only to those preselected ions, resulting in an MS3 experiment with up to a ∼35% reduction in cycle times relative to standard MS3 experiments without loss of sensitivity. We compare the analytical performance of this method with MRMs, as well as standard MS3 experiments, finding equivalent or better performance from the scan-free MS3 method. [ABSTRACT FROM AUTHOR]

Background As a comprehensive discipline that studies food and nutrition, foodomics requires reliable qualitative and quantitative information about the food proteome component in order to extract new integrative information from the complex multivariable space of omics. This new information is necessary to achieve a higher level of understanding of processes in food science and technology, consequently new functions of food and improved markers of food quality and safety and completely transform concept of food safety. Scope and approach We are making an effort to present mass spectrometry (MS) based proteomic approaches that are being utilized in different proteomic studies, not necessarily in the field of foodomics, which are important and have the potential to advance this field. Current analytical capabilities of MS-based proteomics together with sample preparation procedures and quantification strategies, and recent technical developments were presented. Key findings and conclusions MS-based proteomics enables the analysis of different aspects of proteins and provides a variety of approaches for reliable quantification of individual proteins and/or food proteome. This is a complex field and its successful implementation requires a dedicated analyst, a thorough design of sample preparation procedure, the selection of an MS technique and approach, an adequate type of mass spectrometer, a thorough data analysis and validation. Improvements in the technology of mass spectrometers are continuously expanding capabilities of MS-based proteomics. [ABSTRACT FROM AUTHOR]

Detecting megadalton matrix-assisted laser desorption/ionization (MALDI) ions in an ion trap mass spectrometer is a technical challenge. In this study, megadalton protein and polymer ions were successfully measured by MALDI linear ion trap mass spectrometer (LIT-MS) for the first time. The LIT-MS is comprised of a Thermo linear ion trap mass analyzer and a highly sensitive charge-sensing particle detector (CSPD). A newly designed radio frequency (rf) scan mode with dipolar resonance ejection techniques is proposed to extend the mass range of LIT-MS up to one million Thomson (Th). We analyze high mass ions with mass-to charge (m / z) ratios ranging from 100 kTh to 1 MTh, including thyroglobulin, alpha-2-macroglobulin, immunoglobulins (e.g., IgG and IgM), and polymer (∼ 940 kTh) ions. Besides, it is also very challenging for ion trap mass spectrometry to detect megadalton ions at low concentrations. By adopting high affinity carboxylated/oxidized detonation nanodiamonds (oxDNDs) to enrich IgM molecules and form antibody-nanodiamond conjugates, we have successfully reached ∼ 5 nM (5 μg/mL) concentration which is better than that by the other techniques. Three-section linear ion trap (LIT) mass analyzer coupled with charge-sensing particle detector (CSPD) can successfully analyze multiply charged immunoglobulin M ions at nanomolar concentrations. [Display omitted] • MALDI linear ion trap mass spectrometer. • Charge-sensing particle detector. • Detection of megadalton MALDI ions at low concentrations. [ABSTRACT FROM AUTHOR]

Mass spectrometry (MS)-based precursor ion isolation, collision-induced dissociation (CID) fragmentation, and detection using linear ion-trap multiple-stage mass spectrometry (LIT MSn) in combination with high resolution mass spectrometry (HRMS) provides a unique tool for structural characterization of complex mixture without chromatographic separation. This approach permits not only separation of various lipid families and their subfamilies, but also stereoisomers, thereby, revealing the structural details. In this report, we describe the LIT MSn approach to unveil the structures of a 2,3-diacyl trehalose (DAT) family isolated from the cell envelope of Mycobacterium tuberculosis, in which more than 30 molecular species, and each species consisting of up to six isomeric structures were found. LIT MSn performed on both [M + Na]+ and [M + HCO2]− ions of DAT yield complimentary structural information for near complete characterization of the molecules, including the location of the fatty acyl substituents on the trehalose backbone. This latter information is based on the findings of the differential losses of the two fatty acyl chains in the MS2 and MS3 spectra; while the product ion spectra from higher stage LIT MSn permit confirmation of the structural assignment.

Reported herein is a simple method of performing single analyzer precursor ion scans in a linear quadrupole ion trap using orthogonal double resonance excitation. A first supplementary AC signal applied to the y electrodes is scanned through ion secular frequencies in order to mass-selectively excite precursor ions while, simultaneously, a second fixed-frequency AC signal is applied orthogonally on the x electrodes in order to eject product ions of selected mass-to-charge ratios towards the detector. The two AC signals are applied orthogonally so as to preclude the possibility of (1) inadvertently ejecting precursor ions into the detector, which results in artifact peaks, and (2) prevent beat frequencies on the x electrodes from ejecting ions off-resonance. Precursor ion scans are implemented while using the inverse Mathieu q scan for easier mass calibration. The orthogonal double resonance experiment results in single ion trap precursor scans with far less intense artifact peaks than when both AC signals are applied to the same electrodes, paving the way for implementation of neutral loss scanning in single ion trap mass spectrometers. [ABSTRACT FROM AUTHOR]

A dual-polarity linear ion trap (LIT) mass spectrometer was developed in this study, and the method for simultaneously controlling and detecting cations and anions was proposed and realized in the LIT. With the application of an additional dipolar DC field on the ejection electrodes of an LIT, dual-polarity mass spectra could be obtained, which include both the mass-to-charge ( m/z) ratio and charge polarity information of an ion. Compared with conventional method, the ion ejection and detection efficiency could also be improved by about one-fold. Furthermore, ion-ion reactions within the LIT could be dynamically controlled and monitored by manipulating the distributions of ions with opposite charge polarities. This method was then used to control and study the reaction kinetics of ion-ion reactions, including electron transfer dissociation (ETD) and charge inversion reactions. A dual-polarity collision-induced dissociation (CID) experiment was proposed and performed to enhance the sequence coverage of a peptide ion. Ion trajectory simulations were also carried out for concept validation and system optimization. [ABSTRACT FROM AUTHOR]

A linear wire ion trap (LWIT) with both electron ionization (EI) and single photon ionization (SPI) sources was built. The SPI was provided by a vacuum ultraviolet (VUV) lamp with the ability to softly ionize organic compounds. The VUV lamp was driven by a pulse amplifier, which was controlled by a pulse generator, to avoid the detection of photons during ion detection. Sample gas was introduced through a leak valve, and the pressure in the system is shown to affect the signal-to-noise ratio and resolving power. Under optimized conditions, the limit of detection (LOD) for benzene was 80 ppbv using SPI, better than the LOD using EI (137 ppbv). System performance was demonstrated by distinguishing compounds in different classes from gasoline. [ABSTRACT FROM AUTHOR]

A method of fragmenting ions over a wide range of m/ z values while balancing energy deposition into the precursor ion and available product ion mass range is demonstrated. In the method, which we refer to as 'multigenerational collision-induced dissociation', the radiofrequency (rf) amplitude is first increased to bring the lowest m/ z of the precursor ion of interest to just below the boundary of the Mathieu stability diagram (q = 0.908). A supplementary AC signal at a fixed Mathieu q in the range 0.2-0.35 (chosen to balance precursor ion potential well depth with available product ion mass range) is then used for ion excitation as the rf amplitude is scanned downward, thus fragmenting the precursor ion population from high to low m/ z. The method is shown to generate high intensities of product ions compared with other broadband CID methods while retaining low mass ions during the fragmentation step, resulting in extensive fragment ion coverage for various components of complex mixtures. Because ions are fragmented from high to low m/ z, space charge effects are minimized and multiple discrete generations of product ions are produced, thereby giving rise to 'multigenerational' product ion mass spectra. [ABSTRACT FROM AUTHOR]

Ion isolation in a linear ion trap is demonstrated using dual resonance frequencies, which are applied simultaneously. One frequency is used to eject ions of a broad m/ z range higher in m/ z than the target ion, and the second frequency is set to eject a range of ions lower in m/ z. The combination of the two thus results in ion isolation. Despite the simplicity of the method, even ions of low intensity may be isolated since signal attenuation is less than an order of magnitude in most cases. The performance of dual frequency isolation is demonstrated by isolating individual isotopes of brominated compounds. [ABSTRACT FROM AUTHOR]

Steroid analysis is being conquered by liquid chromatography tandem mass spectrometry (LC–MS/MS) benefiting from higher standardization, selectivity and diversity. Regarding high throughput in routine diagnostics rapid chromatography is mandatory. Introducing MS 3 (MS/MS/MS), specificity of mass spectrometric detection can be enhanced without sacrificing analysis time. 100 mL of human plasma/serum, saliva, urine and 10–20 mg of hair are used for the simultaneous quantification of 17α-hydroxyprogesterone, aldosterone, androstenedione, cortisol, cortisone, dehydroepiandrosterone sulfate (DHEAS), estradiol, progesterone, and testosterone using online solid phase extraction (SPE) LC–MS/MS or LC–MS 3 . Steroids can be analyzed in 4 min after a single manual dilution and protein precipitation step. In complex sample matrices like hair MS 3 detection was found to be appropriate for quantitation. Lower limits of quantitation ranged from 37 pmol/L (estradiol) up to 3.1 nmol/L (DHEAS). General accuracy was 89–107% with between-run imprecision ≤10%. Comparison to immunoassays revealed significant differences in quantitation for urinary cortisol (−71% mean), aldosterone (−40% mean) and plasma aldosterone (−45% mean). The comparison of MS 2 and MS 3 quantitation of hair cortisol also revealed significant differences. In general, quantitation via MS 3 was not applicable for a long time. But with the current generation of mass spectrometers quantitation via MS 3 can be superior to MS 2 regarding specificity and accuracy when dealing with matrix issues. However, drawbacks regarding flexibility and precision have to be taken into account. Concludingly, simple protein precipitation combined with rapid online SPE LC–MS/MS/MS allows us to quantify over broad, essential concentration ranges in human serum, saliva, urine and hair. [ABSTRACT FROM AUTHOR]

Space charge effects play important roles in ion trap operations, which typically limit the ion trapping capacity, dynamic range, mass accuracy, and resolving power of a quadrupole ion trap. In this study, a rhombic ion excitation and ejection method was proposed to minimize space charge effects in a linear ion trap. Instead of applying a single dipolar AC excitation signal, two dipolar AC excitation signals with the same frequency and amplitude but 90° phase difference were applied in the x- and y-directions of the linear ion trap, respectively. As a result, mass selective excited ions would circle around the ion cloud located at the center of the ion trap, rather than go through the ion cloud. In this work, excited ions were then axially ejected and detected, but this rhombic ion excitation method could also be applied to linear ion traps with ion radial ejection capabilities. Experiments show that space charge induced mass resolution degradation and mass shift could be alleviated with this method. For the experimental conditions in this work, space charge induced mass shift could be decreased by ~50%, and the mass resolving power could be improved by ~2 times at the same time. [ABSTRACT FROM AUTHOR]

The ion enhanced activation and collision-induced dissociation (CID) by simultaneous dipolar excitation of ions in the two radial directions of linear ion trap (LIT) have been recently developed and tested by experiment. In this work, its detailed properties were further studied by theoretical simulation. The effects of some experimental parameters such as the buffer gas pressure, the dipolar excitation signal phases, power amplitudes, and frequencies on the ion trajectory and energy were carefully investigated. The results show that the ion activation energy can be significantly increased by dual-direction excitation using two identical dipolar excitation signals because of the addition of an excitation dimension and the fact that the ion motion radius related to ion kinetic energy can be greater than the field radius. The effects of higher-order field components, such as dodecapole field on the performance of this method are also revealed. They mainly cause ion motion frequency shift as ion motion amplitude increases. Because of the frequency shift, there are different optimized excitation frequencies in different LITs. At the optimized frequency, ion average energy is improved significantly with relatively few ions lost. The results show that this method can be used in different kinds of LITs such as LIT with 4-fold symmetric stretch, linear quadrupole ion trap, and standard hyperbolic LIT, which can significantly increase the ion activation energy and CID efficiency, compared with the conventional method. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

It is well-known that matrix effects in high performance liquid chromatography coupled to electrospray ionization mass spectrometry (HPLC-ESI-MS) can seriously compromise quantitative analysis and affect method reproducibility. Paired ion electrospray ionization (PIESI) mass spectrometry is an approach for analyzing ultra-low levels of anions in the positive ion mode. This approach uses a structurally optimized ion pairing reagent to post-column associate with the anionic analyte, subsequently forming positively charged complexes. These newly formed complex ions are often more surface-active as compared to either the native anion or the ion pairing reagent. No studies have examined whether or not the PIESI approach mitigates matrix effects. Consequently, a controlled study was done using five analytes in highly controlled and reproducible synthetic groundwater and urine matrices. In addition, two different mass spectrometers (linear ion trap and triple quadrupole) were used. Compared to the negative ion mode, the PIESI-MS approach was less susceptible to matrix effects when performed on two different MS platforms. Using PIESI-MS, less dilution of the sample is needed to eliminate ionization suppression which, in turn, permits lower limits of detection and quantitation. [ABSTRACT FROM AUTHOR]

It is well known that superimposition of some positive octopole field will benefit the performance of ion trapmass analyzer. In the radial-ejection linear ion trap (LIT), adding some octopole field component to the main quadrupole field is usually accomplished by stretching the ejection rod pair. In this study, the effect of octopole potential and some other higher order potential on the performance of LIT mass analyzer is investigated. A simple and effective method, which is to add some octopole component by building a LIT with a pair of rectangular electrodes and a pair of semi-circular electrodes, is reported. Its properties were studied by numerical simulations and experiments. The results showed that a certain amount of positive octopole component could be produced by simply adjusting the position and width of the rectangular electrodes. A resolution of over 1200 at m/z 609 (~1600Da/s) was observed in this type of LIT. They also performed tandem mass spectrometry well. The device with optimum geometry for ion ejection from rectangular electrodes provided comparable performance to that for ion ejection from semicircular electrodes. This type of LIT design is easy for fabrication and assembly. [ABSTRACT FROM AUTHOR]

Mass selective axial ejection (MSAE) from a low pressure linear ion trap (LIT) is investigated in the presence of added auxiliary nonlinear radio frequency (rf) fields. Nonlinear rf fields allow ions to be ejected with high sensitivity at large excitation amplitudes and reduced deleterious effects of space charge. These permit the operation of the LIT at ion populations considerably larger than the space charge limit usually observed in the absence of the nonlinear fields while maintaining good spectral resolution and mass accuracy. Experimental data show that the greater the strength of the nonlinear field, the less the effects of space charge on mass assignment and peak width. The only deleterious effect is a slight broadening of the mass spectral peaks at the highest values of added nonlinear fields used. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A novel linear ion trap mass analyzer featuring half round rod electrodes (HreLIT) has been built. It is mainly composed of two pairs of stainless steel electrodes which have a cross-section of half round rod and a pair of end electrodes. The HreLIT has a simple structure and so it could be assembled by hand with relatively high mechanical accuracy. The external dimension of HreLIT is 50 mm × 29.5 mm × 28 mm (length × width × height) and its internal volume is about 3.8 cm. A home-made HreLIT mass spectrometer with three-stage vacuum system was built and the performance of HreLIT was characterized using reserpine solution and PPG standard solution. When the scan rate was 254 u/s, mass peak with FWHM of 0.14 u was achieved for ions with m/z 609, which corresponds to a mass resolution of 4350. The HreLIT was also operated at a low q value of 0.28 to extend its mass range. The experiment result showed a mass range of over 2800 u and the amplitude of radio frequency (rf) signal was only 1560 V (0-p). Three-stage tandem mass spectrometry was successfully performed in the HreLIT, and the collision-induced dissociation (CID) efficiencies of MS (CID of ions with m/z 609) and MS (CID of ions with m/z 448) were 78% and 59%, respectively. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Listeria monocytogenes ( L. monocytogenes) is a facultative, Gram-positive, food-borne bacterium, which causes serious infections. Although it is known that lipids play important roles in the survival of Listeria, the detailed structures of these lipids have not been established. In this contribution, we described linear ion-trap multiple-stage mass spectrometric approaches with high-resolution mass spectrometry toward complete structural analysis including the identities of the fatty acid substituents and their position on the glycerol backbone of the polar lipids, mainly phosphatidylglycerol, cardiolipin (CL), and lysyl-CL from L. monocytogenes. The location of the methyl side group along the fatty acid chain in each lipid family was characterized by a charge-switch strategy. This is achieved by first alkaline hydrolysis to release the fatty acid substituents, followed by tandem mass spectrometry on their N-(4-aminomethylphenyl) pyridinium (AMPP) derivatives as the M+ ions. Several findings in this study are unique: (1) we confirm the presence of a plasmalogen PG family that has not been previous reported; (2) an ion arising from a rare internal loss of lysylglycerol residue was observed in the MS spectrum of lysyl-CL, permitting its distinction from other CL subfamilies. [ABSTRACT FROM AUTHOR]

Food allergen research has made giant steps in the last years thanks to the features offered by the latest technology of mass analyzers placed on the market allowing multiplex sensitive detection of proteins. Potentials and features of two mass analyzers namely a linear ion trap capable of performing a data dependent or selected reaction monitoring analysis and an OrbitrapTM stand-alone MS enabling a broadband fragmentation without mass selection at highest mass resolving power are herein described and applied to the multiplex screening of allergens in a type of wine chosen as a reference matrix. Quantitative and confirmative capabilities of both platforms were assessed on the specific case study, the multiple detection of egg and milk -related proteins, typically employed in white wines as fining agents. Commercial bioinformatic tools used for a quick allergen identification will be also discussed. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The most common data collection in shotgun proteomics is via data-dependent acquisition (DDA), a process driven by an automated instrument control routine that directs MS/MS acquisition from the highest abundant signals to the lowest. An alternative to DDA is data-independent acquisition (DIA), a process in which a specified range in m/ z is fragmented without regard to prioritization of a precursor ion or its relative abundance in the mass spectrum, thus potentially offering a more comprehensive analysis of peptides than DDA. In this work, we evaluate both DDA and DIA on three different linear ion trap instruments: an LTQ, an LTQ modified with an electrodynamic ion funnel, and an LTQ Velos. These instruments represent both older (LTQ) and newer (LTQ Velos) ion trap designs (i.e., linear versus dual ion traps, respectively), and allow direct comparison of peptide identifications using both DDA and DIA analysis. Further, as the LTQ Velos has an enhanced 'S-lens' ion guide to improve ion flux, we found it logical to determine if the former LTQ model could be leveraged by improving sensitivity by modifying with an electrodynamic ion guide of significantly different design to the S-lens. We find that the ion funnel enabled LTQ identifies more proteins in the insoluble fraction of a yeast lysate than the other two instruments in DIA mode, whereas the faster scanning LTQ Velos performs better in DDA mode. We explore reasons for these results, including differences in scan speed, source ion optics, and linear ion trap design. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Ion trajectory numerical simulation is used to find the linear ion trap excitation contour in the second stability region. The effects of initial conditions, the ejection Mathieu parameter, scan speed, dipole excitation voltage and gas damping are studied. Modeling shows that in the stability region center the resolution power is ≈ 200 000 (at full width half height of a peak, FWHM) at pressure 0.1 mTorr and 100 % excitation efficiency (not taking into account the space charge)., Competing Interests: The authors declare no competing interests., (© 2022 Published by Elsevier Ltd.)

A high precision electric field simulation method is employed to investigate micron-size geometry deviation effects on the electric field distributions as well as on mass resolutions in linear ion traps. Translational and angular displacements within three linear ion traps with different electrode geometries, hyperbolic, circular and rectangular electrodes, were studied. It is found that the linear ion trap with rectangular electrodes is more sensitive to translational displacements, while the linear ion trap with circular electrodes is more sensitive to angular displacements in general. As a guideline, the results could be used in the design and fabrication process of a linear ion trap. [ABSTRACT FROM AUTHOR]

There is a raising demand for sensitive and high throughput MS based methods for screening purposes especially tailored to the detection of allergen contaminants in different food commodities. A challenging issue is represented by complex food matrices where the antibody-based kits commercially available might encounter objective limitations consequently to epitope masking phenomena due to a multitude of interfering compounds arising from the matrix. The performance of a method duly optimized for the extraction and simultaneous detection of soy, egg and milk allergens in a cookie food matrix by microHPLC-ESI-MS/MS, is herein reported. Thanks to the innovative configuration and the versatility shown by the dual cell linear ion trap MS used, the most intense and reliable peptide markers were first identified by untargeted survey experiment, and subsequently employed to design an ad hoc multi-target SRM method, based on the most intense transitions recorded for each selected precursor peptide. A sample extraction and purification protocol was optimized also including an additional step based on sonication, which resulted in a considerable improvement in the detection of milk allergen peptides. Data Dependent™ Acquisition scheme allowed to fill out a tentative list of potential peptide markers, which were further filtered upon fulfilling specific requirements. A total of eleven peptides were monitored simultaneously for confirmation purposes of each allergenic contaminant and the two most sensitive peptide markers/protein were selected in order to retrieve quantitative information. Relevant LODs were found to range from 0.1µg/g for milk to 0.3µg/g for egg and 2µg/g for soy. [ABSTRACT FROM AUTHOR]

This work reports implementation of an optimized linear ion trap (LIT) mass analyzer manufactured using digital light processing (DLP), a low cost rapid prototyping technique. To satisfy requirements for a portable commercial instrument, our previous DLP LIT has been improved by using polymer material for electrodes and housing with higher heat deflection temperature and much improved metal coating of the electrodes. In this way, a polymer-based LIT can operate at higher pressures with more stable voltages, low outgassing and with much longer electrode lifetime. This paper demonstrates non-scanning operation of a DLP LIT based on ceramic resin with specially electroplated electrodes. Non-scanning mode is suitable for applications in which only specific mass fragments are targeted such as security and forensics. Experimental results from a DLP LIT are therefore shown for simulants of cocaine, TNT and sarin. [ABSTRACT FROM AUTHOR]