Coupled Space- and Velocity-Focusing in Time-of-Flight Mass Spectrometry-a Comprehensive Theoretical Investigation

Experimental Validation of Comprehensive Calculation for High-Resolution Linear MALDI-TOF Mass Spectrometry

This work discusses the effectiveness of the previously developed comprehensive calculation model to optimize linear MALDI-TOF mass spectrometers. The model couples space- and velocity-focusing to precisely analyze the flight-time distribution of ions and predict optimal experimental parameters for the highest mass resolving power. Experimental validation was conducted using a laboratory-made instrument to analyze CsI3 and angiotensin I ions in low to medium m/z range. The results indicate that the predicted optimal extraction voltage and delay were reasonably accurate and effective. In the low m/z range, the peak width obtained using optimal parameters reached the sub nanosecond range, corresponding to a mass resolving power of 10 000-17 000, or 20 000-34 000 if shot-to-shot random fluctuations were minimized by the dynamic data correction method. The observed optimal mass resolving power in the current experiment is 4.8-7.8 times that of commercial instruments. Practical limitations resulting in the gap between the observed and theoretical ultimate mass resolving power are discussed.

Method of kinetic energy reconstruction from time-of-flight mass spectra

We present a method for the reconstruction of ion kinetic energy distributions from ion time-of-flight mass spectra through ion trajectory simulations. In particular, this method is applicable to complicated spectrometer geometries with largely anisotropic ion collection efficiencies. A calibration procedure using a single ion mass peak allows the accurate determination of parameters related to the spectrometer calibration, experimental alignment, and instrument response function, which improves the agreement between simulations and experiment. The calibrated simulation is used to generate a set of basis functions for the time-of-flight spectra, which are then used to transform from time-of-flight to kinetic-energy spectra. We demonstrate this reconstruction method on a recent pump-probe experiment by Asmussen et al. [Asmussen et al., Phys. Chem. Chem. Phys., 23, 15138, (2021)] on helium nanodroplets and retrieve time-resolved kinetic-energy-release spectra for the ions from ion time-of-flight spectra.

Advances in high-resolution mass spectrometry techniques for analysis of high mass-to-charge ions

A major challenge in modern mass spectrometry (MS) is achieving high mass resolving power and accuracy for precision analyses in high mass-to-charge (m/z) regions. To advance the capability of MS for increasingly demanding applications, understanding limitations of state-of-the-art techniques and their status in applied sciences is essential. This review summarizes important instruments in high-resolution mass spectrometry (HRMS) and related advances to extend their working range to high m/z regions. It starts with an overview of HRMS techniques that provide adequate performance for macromolecular analysis, including Fourier-transform, time-of-flight (TOF), quadrupole-TOF, and related data-processing techniques. Methodologies and applications of HRMS for characterizing macromolecules in biochemistry and material sciences are summarized, such as top-down proteomics, native MS, drug discovery, structural virology, and polymer analyses.

Active Humoral Response Reverts Tumorigenicity through Disruption of Key Signaling Pathway

Immune checkpoint inhibitors such as monoclonal antibodies (mAbs) are amongst the most important breakthroughs in cancer therapeutics. However, high cost and short acting time limits its affordability and clinical application. Therefore, an economical and durable alternative is urgently needed. Previously, we identified an IL-17RB targeting mAb which intercepts IL-17B/IL-17RB signal transduction and suppresses tumorigenesis in many types of cancer. We reason that active immunity against the antigenic epitope of IL-17RB can reproduce the anti-cancer effect of mAbs with better sustainability. Here, we present a cancer vaccine composed of multiple synthesized epitope peptides chemically conjugated onto CRM197, a highly immunogenic carrier protein. Combining mass spectrometry with immunoassay, we standardized hapten density determination and optimized vaccine design. Furthermore, orthotopically transplanted syngeneic mouse tumor 4T1 showed that administration of this vaccine therapeutically mitigates primary cancer growth as well as distance metastasis. In conclusion, we demonstrate preparation, characterization and pre-clinical application of a novel peptide cancer vaccine.

High-performance miniature linear time-of-flight mass spectrometry as an advantageous tool in a high mass-to-charge range

A newly developed miniature MALDI-TOF mass spectrometer provides superior performance in a high m/z range.

Low-Energy Electron Inelastic Mean Free Path of Graphene Measured by a Time-of-Flight Spectrometer

The detailed examination of electron scattering in solids is of crucial importance for the theory of solid-state physics, as well as for the development and diagnostics of novel materials, particularly those for micro- and nanoelectronics. Among others, an important parameter of electron scattering is the inelastic mean free path (IMFP) of electrons both in bulk materials and in thin films, including 2D crystals. The amount of IMFP data available is still not sufficient, especially for very slow electrons and for 2D crystals. This situation motivated the present study, which summarizes pilot experiments for graphene on a new device intended to acquire electron energy-loss spectra (EELS) for low landing energies. Thanks to its unique properties, such as electrical conductivity and transparency, graphene is an ideal candidate for study at very low energies in the transmission mode of an electron microscope. The EELS are acquired by means of the very low-energy electron microspectroscopy of 2D crystals, using a dedicated ultra-high vacuum scanning low-energy electron microscope equipped with a time-of-flight (ToF) velocity analyzer. In order to verify our pilot results, we also simulate the EELS by means of density functional theory (DFT) and the many-body perturbation theory. Additional DFT calculations, providing both the total density of states and the band structure, illustrate the graphene loss features. We utilize the experimental EELS data to derive IMFP values using the so-called log-ratio method.

A Dynamic Data Correction Method for Enhancing Resolving Power of Integrated Spectra in Spectroscopic Analysis

A dynamic data correction method embedded in the process of data acquisition improves spectral quality. The method minimizes the impact of random errors in spectroscopic measurements by correcting peak positions in every single-scan spectrum. The method is fast enough to facilitate online data correction. The integration of corrected spectra improves resolving power and signal-to-noise ratio. The correction method can apply to most analytical spectra. In mass spectrometry and Raman spectroscopy, observations show that it improved the average resolving power by roughly 40-150% and revealed unresolved spectral features.

Impact of uneven sample morphology on mass resolving power in linear MALDI-TOF mass spectrometry: A comprehensive theoretical investigation

This work discusses the correlation between the mass resolving power of matrix-assisted laser desorption/ionization time-of-flight mass analyzers and extraction condition with an uneven sample morphology. Previous theoretical calculations show that the optimum extraction condition for flat samples involves an ideal ion source design and extraction delay. A general expression of spectral feature takes into account ion initial velocity, and extraction delay is derived in the current study. The new expression extends the comprehensive calculation to uneven sample surfaces and above 90% Maxell-Boltzmann initial velocity distribution of ions to account for imperfect ionization condition. Calculation shows that the impact of uneven sample surface or initial spatial spread of ions is negligible when the extraction delay is away from the ideal value. When the extraction delay approaches the optimum value, the flight-time topology shows a characteristic curve shape, and the time-domain mass spectral feature broadens with an increase in initial spatial spread of ions. For protonated 2,5-dihydroxybenzoic acid, the mass resolving power obtained from a sample of 3-μm surface roughness is approximately 3.3 times lower than that of flat samples. For ions of m/z 3000 coexpanded with 2,5-dihydroxybenzoic acid, the mass resolving power in the 3-μm surface roughness case only reduces roughly 7%. Comprehensive calculations also show that the mass resolving power of lighter ions is more sensitive to the accuracy of the extraction delay than heavier ions.