International Journal of Mass Spectrometry最新文献

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.

The Velocity Slice Imaging technique has revolutionized charged particle-molecule interaction studies in general and electron-molecule interaction studies in particular. Multiple electrostatic lens assemblies are often used in spectrometers for resolving low kinetic energy fragments. In a crossed-beam experiment with an effusive molecular beam as a target, the background gas forms a strong extended source of ions where the charged particle beam is used as a projectile without focusing. This extended source creates artefacts on the momentum images as we try to magnify them beyond a certain size. Here, we present a systematic study of this effect on momentum imaging in the low-energy-electron molecule collisions as an example and the solutions to address this issue by background subtraction with suitable magnification. Additionally, we demonstrated that a supersonic molecular beam target helps minimize these artefacts in the image magnification by reducing the background signal. These systematic findings may bring valuable insight into the investigation of low kinetic energy release processes involving electron impact, ion impact, and merge beam experiments with large interaction volumes where high magnification is essential.

Metal ions play major roles in the functioning of biological systems. In our previous work, site-specific sodiation of gramicidin S (G), which is a cyclic antiparallel β-sheet consisting of four intramolecular N–H⋅⋅⋅OC hydrogen bonds, was examined. It was found that amide N–H bonds in [G + nH]ⁿ⁺ with n = 1 and 2 were deprotonated to form [G + nH − mH + mNa]ⁿ⁺ with m up to 7 and 8, respectively, in a 1 mM NaOH water/methanol (1/1) solution. In this work, sodiation of melittin (MEL) which is composed of two α-helices was studied. In a 1 mM NaOH solution, the maximum number of m for [MEL + nH − mH + mNa]ⁿ⁺ was found to increase with n, i.e., m = 4 for n = 2, m = 5 for n = 3, and m = 8 for n = 4. This suggests the occurrence of partial denaturation of the α-helix with an increase in n. The denaturation may be caused by loosening of intramolecular amide hydrogen bonds in the C-terminus side of MEL which is composed of 4 basic residues. For further investigation, sodiation of cytochrome c composed of α-helices, and ubiquitin composed of α-helices and a β-sheet was examined. In a 1 mM NaOH water/methanol solution, cytochrome c maintains its native conformation and only 9 acidic sites in addition to 15 carboxylic groups (total 24) are sodiated. This suggests that cytochrome c is resistive to sodiation in a 1 mM NaOH solution. In contrast to cytochrome c, denaturation of ubiquitin was observed in a 1 mM NaOH water/methanol solution. This suggests that β-sheet is less resistive to sodiation than α-helix. The denatured ubiquitin may have a molten globule conformation due to the presence of folded α-helices that act as hinges to prevent extensive unfolding.

Matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD) with reducing matrices enables rapid mass spectrometric characterization of intact proteins. Several novel matrices have been developed for improving the fragmentation efficiency of MALDI-ISD. In particular, matrix having aniline group stronger facilitate MALDI-ISD than that having phenol group. Because the aniline N–H bond is stronger than the phenol O–H bond, the efficient fragmentation induced using matrices containing aniline group cannot be explained by the previously proposed mechanism involving the matrix-peptide hydrogen atom transfer. To explain these phenomena, electron transfer from the matrix to the peptide was recently proposed as the initial step in the MALDI-ISD processes. In this study, to estimate whether a peptide acquires hydrogen atoms or electrons in the first step of MALDI-ISD, the transition-state barriers of the reaction between dipeptide and hydrogen atoms produced from the excited-state matrix were calculated, assuming the peptide in the ground state during the MALDI-ISD process. The barrier obtained for the corresponding hydrogen atom attachment reaction did not correlate with the yield of the fragment ions produced by MALDI-ISD. In contrast, a correlation has been reported between the yields of the fragment ions produced by MALDI-ISD and the ionization energy of the matrix solids, indicating that MALDI-ISD occurs efficiently using a matrix that easily emits electrons. These results strongly suggest that MALDI-ISD of peptides using reducing matrices is well explained by the transfer of electrons and subsequent protons from the matrix to the peptide.

The measurement of volatile organic compounds (VOCs) originating from organisms allows continuous monitoring and a unique insight into the metabolism. One method offering the sensitivity to detect these VOCs is secondary electrospray ionization coupled to high-resolution mass spectrometry (SESI-HRMS). SESI was derived from electrospray ionization (ESI) and has found widespread application in clinical research and monitoring of animals. This review discusses the technical aspects behind SESI, the advancements, and the technical hurdles faced. Additionally, the recent advances in the applications of SESI in human and animal-centered research are presented.

Terpenes are an incredibly diverse category of chemical compounds, featuring a variety of structural features and modifications. This work focuses on the monocyclic monoterpene (C₁₀H₁₆) limonene and one of its hydrated derivatives α-terpineol. Previous experiments have shown that these compounds may become protonated under atmospheric conditions. It was of interest to provide greater detail in how these compounds would break down following protonation, where previous studies lacked mechanistic detail. To overcome these shortcomings, our lab applied combined experimental and theoretical approaches. Tandem mass spectrometry experiments were used to yield the protonated compounds, and collision induced dissociation to break them apart, identifying underlying unimolecular reaction channels of the protonated target. The experimental data is supplemented with density functional theory calculations, which are used to model the individual transformations involved in each of the experimentally observed reaction channels. The mass spectrometry experiments revealed four fragmentation channels in the case of protonated limonene, two major ones and two minor ones, in terms of relative abundance. The neutral loss of C₄H₈ was the most abundant product ion channel, followed by the neutral loss of C₃H₆. The other two fragmentation pathways were minor, and lead to the neutral losses of C₂H₄ and C₃H₈. Density functional theory and RRKM calculations revealed the mechanisms by which these reactions occurred and were shown to be consistent with the experimental data. In the case of protonated α-terpineol, a single fragmentation channel was observed, leading to the neutral loss of water, although sequential fragmentation that was similar to protonated limonene was observed. These observations were justified through calculations, showing that a relatively stable α-terpineol ion-molecule complex is formed in the source, leading to the observed chemistry.

We have developed a multichannel phase-locked sine waveform generator for a mass dispersive rotating electric field device, known as a rotating wall mass analyzer (RWMA). The waveform generator outputs eight sine waves phase shifted by 45°. The frequency of the waveforms is adjustable in the range of 0.1–100 kHz and the maximum amplitude is 100 V_p-p, which is greater than 20 V_p-p provided by commercial arbitrary waveform generators. Adjustment of either amplitude or frequency maintains phase alignment for all eight output channels to continually generate a uniform rotating electric field inside the RWMA. The RWMA is a high-throughput mass analyzer for preparative mass spectrometry that separates a multicomponent continuous ion beam in space and enables the deposition of ions of different m/z onto concentric ring shapes on surfaces. Here, we demonstrate that increasing the generator's amplitude from 20 V_p-p to 50 V_p-p resolves a continuous ion beam of ubiquitin charge states with a measured mass resolution (m/Δm) of R = 14. This resolution improves to R = 26 for a 100 V_p-p generator output. Furthermore, the designed waveform generator facilitates a single m/z calibration of the rotating electric field parameters to extract a m/z value from a measured radius. These parameters are shown to be valid for other m/z species, ion beam kinetic energies, and ionization polarity modes.