Journal of the American Society for Mass Spectrometry最新文献

Investigating and manipulating the ion–molecule reactions within the ionization source of ion mobility spectrometry (IMS) or mass spectrometry can contribute to developing advanced ionization sources and novel analytical techniques. In this study, a pressure-tunable photoionization tandem ion mobility spectrometer (PI-tandem-IMS) was developed to investigate the ionization suppression caused by unusual proton transfer reactions in dual-analyte systems in which high proton affinity (PA) ions are deprotonated by low PA molecules. The proton transfer reaction mechanisms in the toluene–acetone and toluene–ethanol systems were studied. The experimental results showed the linear correlation between the ln(S_X2H⁺·K_0(T⁺₎/S_T⁺·K_0(X2H⁺₎ + 1) and the square of the reactant concentration c_X², as well as the cubic power of the pressure p³. Based on this, the generation of the proton-bound dimers in the toluene–acetone and toluene–ethanol systems was assigned as a termolecular process. The reaction rate coefficients k of the toluene–acetone and toluene–ethanol systems were calculated at different temperatures, and the Arrhenius plot showed that rate coefficients were both negatively correlated with temperature, implying that elevated temperatures suppress the proton transfer reaction. At 313.15 K, the calculated k values for the toluene–acetone and the toluene–ethanol systems were 2.2 × 10^–26 cm⁶/s and 5.2 × 10^–28 cm⁶/s, respectively, suggesting a higher inhibitory effect of acetone on toluene ionization than that of ethanol. Besides, the suppressive effect of reducing the pressure or increasing the reaction region electric field strength on proton transfer reactions was shown, which demonstrated the PI-tandem IMS was a good tool for understanding ion–molecule reactions in the ionization source.

Additional multipole fields are unavoidable in real quadrupole linear ion traps (QLITs) and play a crucial role in influencing their performance. In this study, the impact of these multipole fields on ion ejection and dynamics in QLITs is exhaustively analyzed using a vectorized Runge–Kutta method and a comprehensive theoretical model of ion vibration involving all the common multipole fields. The comparison of nonlinear resonance under different added multipole fields reveals obvious ion ejection from hexapole and octopole resonances as well as multiple resonance points in most multipole fields. Ion ejection with dipole excitation under these fields demonstrates distinct variations at different excitation working values, influenced by the inherent power distribution of ion motion in a linear quadrupole and the energy dispersion caused by the added multipole fields at varying stability parameters. Furthermore, theoretical and numerical analyses of ion dynamics mutually validate each other, offering the first comprehensive demonstration of ion excitation responses under various multipole fields across a wide stability range. The results show that for positive even-order multipole fields, forward scans lead to lower and more stable maximum amplitude responses compared to reverse scans, while the opposite is true for negative fields. In hexapole fields, the forward scan responses are lower than the reverse scan responses, and both increase sharply near nonlinear resonance points, regardless of field polarity. This work provides a thorough theoretical foundation for optimizing multipole field applications in QLITs.

Collision induced dissociation (CID) and collision induced unfolding (CIU) experiments are important tools for determining the structures of and differences between biomolecular complexes with mass spectrometry. However, quantitative comparison of CID/CIU data acquired on different platforms or even using different regions of the same instrument can be very challenging due to differences in gas identity and pressure, electric fields, and other experimental parameters. In principle, these can be reconciled by a detailed understanding of how ions heat, cool, and dissociate or unfold in time as a function of these parameters. Fundamental information needed to model these processes for different ion types and masses is their heat capacity as a function of the internal (i.e., vibrational) temperature. Here, we use quantum computational theory to predict average heat capacities as a function of temperature for a variety of model biomolecule types from 100 to 3000 K. On a degree-of-freedom basis, these values are remarkably invariant within each biomolecule type and can be used to estimate heat capacities of much larger biomolecular ions. We also explore effects of ion heating, cooling, and internal energy distribution as a function of time using a home-built program (IonSPA). We observe that these internal energy distributions can be nearly Boltzmann for larger ions (greater than a few kDa) through most of the CID/CIU kinetic window after a brief (few-μs) induction period. These results should be useful in reconciling CID/CIU results across different instrument platforms and under different experimental conditions, as well as in designing instrumentation and experiments to control CID/CIU behavior.

There are many reasons to consider postdoctoral research after completing a Ph.D. For those interested in academic careers at all levels, a postdoctoral research associate (PDRA) position is often required or at least preferred. Even for those interested in industry, government, or alternative careers, postdoctoral research provides opportunities to expand your knowledge and skill sets beyond your Ph.D. training. It can be a wonderful time to focus on research with minimal distractions and interruptions. However, there has been little discussion about the challenges of the postdoc transition. The postdoc experience can vary widely, but common challenges include transitioning into a new environment, learning new skills, serving in multiple roles as a mentor and mentee, different and sometimes unclear positions in the institution, and competition for limited opportunities. In this Commentary, we draw on our personal experiences and interviews with postdocs of various backgrounds and intersectionalities (gender, race, first-gen, neurodiversity, etc.) to discuss how to successfully navigate various aspects of the postdoc experience. Our perspective comes primarily within mass spectrometry (MS) research, but the interviews include several experiences outside of the MS field to develop discussions applicable to a broad range of PDRA experiences.

Per- and polyfluoroalkyl substances (PFAS) are contaminants of increasing concern, with over seven million compounds currently inventoried in the PubChem PFAS Tree. Recently, ion mobility spectrometry has been combined with liquid chromatography and high-resolution mass spectrometry (LC-IMS-HRMS) to assess PFAS. Interestingly, using negative electrospray ionization, perfluoroalkyl carboxylic acids (PFCAs) form homodimers ([2M-H]⁻), a phenomenon observed with trapped, traveling wave, and drift-tube IMS. In addition to the limited research on their effect on analytical performance, there is little information on the conformations these dimers can adopt. This study aimed to propose most probable conformations for PFCA dimers. Based on qualitative analysis of how collision cross section (CCS) values change with the mass-to-charge ratio (m/z) of PFCA ions, the PFCA dimers were hypothesized to likely adopt a V-shaped structure. To support this assumption, in silico geometry optimizations were performed to generate a set of conformers for each possible dimer. A CCS value was then calculated for each conformer using the trajectory method with Lennard-Jones and ion-quadrupole potentials. Among these conformers, at least one of the ten lowest-energy conformers identified for each dimer exhibited theoretical CCS values within a ±2% error margin compared to the experimental data, qualifying them as plausible structures for the dimers. Our findings revealed that the fluorinated alkyl chains in the dimers are close to each other due to a combination of C–F···O=C and C–F···F–C stabilizing interactions. These findings, together with supplementary investigations involving environmentally relevant cations, may offer valuable insights into the interactions and environmental behavior of PFAS.

Mass spectrometry (MS) has become an essential tool in virtually all academic, pharmaceutical, and biopharmaceutical analytical laboratories. The specialized and bespoke area of MS research and application of high m/z ion (>m/z 6000 and high mass, >150 kDa) formation, transmission, analysis, and detection is a relatively new area of focus for MS that has seen dramatic acceleration in interest over the last two decades. Herein we delve into this exciting aspect of MS, discussing how MS instrumentation has been refined and evolved for native-MS analysis. We cover the early groundbreaking experiments showing high m/z ion formation, transmission, and preservation of protein structure in the gas phase. Additionally, we discuss specific instrument optimizations and modifications that have advanced high m/z ion generation, transmission, analysis, and detection, contributing to the research area known as gas-phase structural biology. Native-MS sample introduction methods, emerging technologies, and future perspectives are also examined. Finally, we share personal opinions, observations, and experiences that are new to the community or previously unpublished.

Paper spray mass spectrometry (PS-MS) often employs laser cutting to prepare paper substrates, potentially inducing localized thermal decomposition of the cellulose backbone. This work investigates how cellulose pyrolysis products and inherent background molecules within the paper affect PS-MS signal quality and evaluates paper pretreatment methods to enhance performance. Comparative analyses of laser-cut and razor-cut paper using mass spectrometry and ultraviolet–visible spectroscopy (UV–vis) showed significant differences. Laser-cut paper exhibited elevated MS blank signals and higher absorbance in the 200–400 nm UV region, indicating increased chemical abundance and complexity. Gas chromatography–mass spectrometry (GC-MS) identified over 20 residual compounds on laser-cut paper absent in razor-cut samples, half of which were identified as known cellulose pyrolysis products. Washing the paper substrates with methanol, water, or dilute nitric acid significantly reduced both pyrolysis products and background molecules, with water showing the most improvement. Analyses of morphine, fentanyl, methamphetamine, voriconazole, and fluconazole showed no reduction in the signal after washing, with fentanyl and methamphetamine exhibiting a significantly increased MS signal, regardless of the cutting method. This work reveals that while pyrolysis products from laser cutting contribute to increased chemical noise, inherent background molecules in the paper also play a significant role. A simple water wash mitigates both issues, potentially improving the overall PS-MS performance for a range of analytes.

Accurately assigning formulas to thousands of peaks generated by ultrahigh resolution mass spectrometry in a single analysis poses a significant challenge, especially when dealing with diverse molecular compositions across complex mixtures. This difficulty is further compounded by the lack of an established universal mass calibration and formula assignment method. We have developed HRMS-Viewer, a Python-based software tool designed for processing ultrahigh resolution mass spectrometry data specific to petroleum and natural organic matter (NOM). The software employs an efficient, experience-driven approach for small molecule formula assignment, offering a streamlined yet intuitive workflow. Key features include advanced noise reduction, automatic or manual recalibration, real-time visualization of formula assignment results, and options for manual correction. During the workflow, HRMS-Viewer enables the visualization and manual control of critical steps including noise reduction, recalibration, peak identification, and data review.