Energy deposition during electron-induced dissociation

AbstractWe report studies of the internal energy deposited during activation of mass-selected ions through electron-ion collisions. Characteristic fragmentations of the molecular ion of limonene and W(CO)n+ (n = 1-6) indicate that electron-induced dissociation in a Fourier transform ion cyclotron resonance mass spectrometer proceeds via multiple collisions and that the average internal energy deposited during the activation process can be selected to be similar to that associated with electron-impact ionization. Control of the degree of ion excitation through selection of the electron energy, flux, and interaction time with the ions of interest is demonstrated, and advantages of this promising activation technique are discussed

The 3D OrbiSIMS—label-free metabolic imaging with subcellular lateral resolution and high mass-resolving power

We report the development of a 3D OrbiSIMS instrument for label-free biomedical imaging. It combines the high spatial resolution of secondary ion mass spectrometry (SIMS; under 200 nm for inorganic species and under 2 μm for biomolecules) with the high mass-resolving power of an Orbitrap (>240,000 at m/z 200). This allows exogenous and endogenous metabolites to be visualized in 3D with subcellular resolution. We imaged the distribution of neurotransmitters—gamma-aminobutyric acid, dopamine and serotonin—with high spectroscopic confidence in the mouse hippocampus. We also putatively annotated and mapped the subcellular localization of 29 sulfoglycosphingolipids and 45 glycerophospholipids, and we confirmed lipid identities with tandem mass spectrometry. We demonstrated single-cell metabolomic profiling using rat alveolar macrophage cells incubated with different concentrations of the drug amiodarone, and we observed that the upregulation of phospholipid species and cholesterol is correlated with the accumulation of amiodarone

A comparative study of ion activation processes in mass spectrometry

This thesis examines and compares several ion formation and activation techniques used in mass spectrometry, including, charge exchange, collision-induced dissociation, surface-induced dissociation, electron-induced decomposition, and photodissociation. Fragmentation recorded for the molecular ion of the organic molecule, limonene, is used to compare the energy transfer associated with each of these activation techniques. In a second experiment, the distribution $P(\epsilon)$ of internal energies deposited into an ion upon activation is determined using a simple thermochemical procedure based on the appearance energies from a series of decarbonylation reactions from metal carbonyl ions. $P(\epsilon)$ distributions of tungsten hexacarbonyl molecular ions following collisional activation at electron and kiloelectron volt energies were compared for several atomic, diatomic and polyatomic target gases. The difference in energy deposition at the two collision energies was attributed to different mechanisms (electronic and vibrational excitation) of activation. Kiloelectron volt angle-resolved collision-induced dissociation (ARMS) experiments were performed on tungsten hexacarbonyl and iron pentacarbonyl molecular ions at small scattering angles ($\u3c$2.5\sp\circ) at 1.5, 2 and 3 keV collision energies. The average internal energy deposited into the ion increased by more than 5 eV as the scattering angle ($\theta$) is raised from 0 to 2.5\sp\circ. The average internal energy also increased with the kinetic energy of the ion ($E$) and the mass of the target. The $P(\epsilon)$ distributions acquired upon collisional activation for ions scattered through small angles upon 3 keV collision are bimodal in shape. the lower energy component in the distribution is thought to be due to electronic excitation, while the higher energy component is associated with a vibrational excitation mechanism. $P(\epsilon)$ distributions were also determined for tungsten hexacarbonyl ions formed by charge exchange with singly and doubly charged rare gas ions. The energy transferred varied with the recombination energy of the ion. A large fraction of the kinetic energy of the rare gas ion was also transferred during charge exchange at energies between 2 and 10 eV. Charge exchange between doubly charged rare gas ions and tungsten hexacarbonyl resulted in the formation of doubly charged ions. Singly charged ions were also recorded due to a single electron transfer from the doubly charged rare gas ion. Kinetic energy release measurements for reaction between doubly charged transition-metal ions and tungsten hexacarbonyl showed that the average energy released by the reactants upon transfer of a single electron is approximately 2 eV

Dynamic Range of Mass Accuracy in LTQ Orbitrap Hybrid Mass Spectrometer

Using a novel orbitrap mass spectrometer, the authors investigate the dynamic range over which accurate masses can be determined (extent of mass accuracy) for short duration experiments typical for LC/MS. A linear ion trap is used to selectively fill an intermediate ion storage device (C-trap) with ions of interest, following which the ensemble of ions is injected into an orbitrap mass analyzer and analyzed using image current detection and fast Fourier transformation. Using this technique, it is possible to generate ion populations with intraspectrum intensity ranges up to 104. All measurements (including ion accumulation and image current detection) were performed in less than 1 s at a resolving power of 30,000. It was shown that 5-ppm mass accuracy of the orbitrap mass analyzer is reached with >95% probability at a dynamic range of more than 5000, which is at least an order of magnitude higher than typical values for time-of-flight instruments. Due to the high resolving power of the orbitrap, accurate mass of an ion could be determined when the signal was reliably distinguished from noise (S/Np-p>2…3)

Surface-Induced Dissociation of Noncovalent Protein Complexes in an Extended Mass Range Orbitrap Mass Spectrometer

Herein we demonstrate the first adaptation of surface-induced dissociation in a modified high-mass range, high-resolution Orbitrap mass spectrometer. The SID device was designed to be installed in the Q-Exactive series of Orbitrap mass spectrometers with minimal disruption of standard functions. The performance of the SID-Orbitrap instrument has been demonstrated with several protein complex and ligand-bound protein complex systems ranging from 53 to 336 kDa. We also address the effect of ion source temperature on native protein-ligand complex ions as assessed by SID. Results are consistent with previous findings on quadrupole time-of-flight instruments and suggest that SID coupled to high-resolution MS is well-suited to provide information on the interface interactions within protein complexes and ligand-bound protein complexes. <br /

From Protein Complexes to Subunit Backbone Fragments: A Multi-stage Approach to Native Mass Spectrometry

Native mass spectrometry (MS) is becoming an important integral part of structural proteomics and system biology research. The approach holds great promise for elucidating higher levels of protein structure: from primary to quaternary. This requires the most efficient use of tandem MS, which is the cornerstone of MS-based approaches. In this work, we advance a two-step fragmentation approach, or (pseudo)-MS³, from native protein complexes to a set of constituent fragment ions. Using an efficient desolvation approach and quadrupole selection in the extended mass-to-charge (<i>m</i>/<i>z</i>) range, we have accomplished sequential dissociation of large protein complexes, such as phosporylase B (194 kDa), pyruvate kinase (232 kDa), and GroEL (801 kDa), to highly charged monomers which were then dissociated to a set of multiply charged fragmentation products. Fragment ion signals were acquired with a high resolution, high mass accuracy Orbitrap instrument that enabled highly confident identifications of the precursor monomer subunits. The developed approach is expected to enable characterization of stoichiometry and composition of endogenous native protein complexes at an unprecedented level of detail