skip to main content

Title: An ion mobility mass spectrometer coupled with a cryogenic ion trap for recording electronic spectra of charged, isomer-selected clusters

Infrared and electronic spectra are indispensable for understanding the structural and energetic properties of charged molecules and clusters in the gas phase. However, the presence of isomers can potentially complicate the interpretation of spectra, even if the target molecules or clusters are mass-selected beforehand. Here, we describe an instrument for spectroscopically characterizing charged molecular clusters that have been selected according to both their isomeric form and their mass-to-charge ratio. Cluster ions generated by laser ablation of a solid sample are selected according to their collision cross sections with helium buffer gas using a drift tube ion mobility spectrometer and their mass-to-charge ratio using a quadrupole mass filter. The mobility- and mass-selected target ions are introduced into a cryogenically cooled, three-dimensional quadrupole ion trap where they are thermalized through inelastic collisions with an inert buffer gas (He or He/N2mixture). Spectra of the molecular ions are obtained by tagging them with inert atoms or molecules (Ne and N2), which are dislodged following resonant excitation of an electronic transition, or by photodissociating the cluster itself following absorption of one or more photons. An electronic spectrum is generated by monitoring the charged photofragment yield as a function of wavelength. The capacity of the instrument is illustrated with the resonance-enhanced photodissociation action spectra of carbon clusters ([Formula: see text]) and polyacetylene cations (HC2 nH+) that have been selected according to the mass-to-charge ratio and collision cross section with He buffer gas and of mass-selected [Formula: see text] and Au2Ag+clusters.

more » « less
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  ;  ;  ;  ;  ;  
Publisher / Repository:
American Institute of Physics
Date Published:
Journal Name:
Review of Scientific Instruments
Page Range / eLocation ID:
Article No. 043201
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. The structural stability of biomolecules in the gas phase remains an important topic in mass spectrometry applications for structural biology. Here, we evaluate the kinetic stability of native-like protein ions using time-dependent, tandem ion mobility (IM). In these tandem IM experiments, ions of interest are mobility-selected after a first dimension of IM and trapped for up to ∼14 s. Time-dependent, collision cross section distributions are then determined from separations in a second dimension of IM. In these experiments, monomeric protein ions exhibited structural changes specific to both protein and charge state, whereas large protein complexes did not undergo resolvable structural changes on the timescales of these experiments. We also performed energy-dependent experiments, i.e., collision-induced unfolding, as a comparison for time-dependent experiments to understand the extent of unfolding. Collision cross section values observed in energy-dependent experiments using high collision energies were significantly larger than those observed in time-dependent experiments, indicating that the structures observed in time-dependent experiments remain kinetically trapped and retain some memory of their solution-phase structure. Although structural evolution should be considered for highly charged, monomeric protein ions, these experiments demonstrate that higher-mass protein ions can have remarkable kinetic stability in the gas phase. 
    more » « less
  2. Abstract

    Phosphorylated proteins play essential roles in many cellular processes, and identification and characterization of the relevant phosphoproteins can help to understand underlying mechanisms. Herein, we report a collision‐induced dissociation top‐down approach for characterizing phosphoproteins on a quadrupole time‐of‐flight mass spectrometer. β‐casein, a protein with two major isoforms and five phosphorylatable serine residues, was used as a model. Peaks corresponding to intact β‐casein ions with charged states up to 36+were detected. Tandem mass spectrometry was performed on β‐casein ions of different charge states (12+, and 15+to 28+) in order to determine the effects of charge state on dissociation of this protein. Most of the abundant fragments corresponded to y, b ions, and internal fragments caused by cleavage of the N‐terminal amide bond adjacent to proline residues (Xxx‐Pro). The abundance of internal fragments increased with the charge state of the protein precursor ion; these internal fragments predominantly arose from one or two Xxx‐Pro cleavage events and were difficult to accurately assign. The presence of abundant sodium adducts of β‐casein further complicated the spectra. Our results suggest that when interpreting top‐down mass spectra of phosphoproteins and other proteins, researchers should consider the potential formation of internal fragments and sodium adducts for reliable characterization.

    more » « less
  3. Abstract

    Alkali and alkaline earth metal adducts of a branched glycan, XXXG, were analyzed with helium charge transfer dissociation (He‐CTD) and low‐energy collision‐induced dissociation (LE‐CID) to investigate if metalation would impact the type of fragments generated and the structural characterization of the analyte. The studied adducts included 1+ and 2+ precursors involving one or more of the cations: H+, Na+, K+, Ca2+, and Mg2+. Regardless of the metal adduct, He‐CTD generated abundant and numerous glycosidic and cross‐ring cleavages that were structurally informative and able to identify the 1,4‐linkage and 1,6‐branching patterns. In contrast, the LE‐CID spectra mainly contained glycosidic cleavages, consecutive fragments, and numerous neutral losses, which complicated spectral interpretation. LE‐CID of [M + K + H]2+and [M + Na]+precursors generated a few cross‐ring cleavages, but they were not sufficient to identify the 1,4‐linkage and 1,6‐branching pattern of the XXXG xyloglucan. He‐CTD predominantly generated 1+ fragments from 1+ precursors and 2+ product ions from 2+ precursors, although both LE‐CID and He‐CTD were able to generate 1+ product ions from 2+ adducts of magnesium and calcium. The singly charged fragments derive from the loss of H+from the metalated product ions and the formation of a protonated complementary product ion; such observations are similar to previous reports for magnesium and calcium salts undergoing electron capture dissociation (ECD) activation. However, during He‐CTD, the [M + Mg]2+precursor generated more singly charged product ions than [M + Ca]2+, either because Mg has a higher second ionization potential than Ca or because of conformational differences and the locations of the charging adducts during fragmentation. He‐CTD of the [M + 2Na]2+and the [M + 2 K]2+precursors generated singly charged product ions from the loss of a sodium ion and potassium ion, respectively. In summary, although the metal ions influence the mass and charge state of the observed product ions, the metal ions had a negligible effect on the types of cross‐ring cleavages observed.

    more » « less
  4. Ion mobility spectrometry (IMS) using Structures for Lossless Ion Manipulations (SLIM) is an emerging powerful tool for rapid isomer separations. This technology offers high mobility resolution due to prolonged ion mobility path lengths that are achieved on a small form factor separation device. In this work, we interface SLIM IMS separation with a chemical ionization source, which allows one to sample from the gas- and particle-phases directly. As such, one can monitor dynamic isomer populations in ambient air in real-time without prior sample preparation. This technology opens the door to new possibilities in atmospheric chemistry where isomer distribution is expected to play a key role in gas phase processes and in the formation of organic aerosols. The CI-IMS-TOF instrument built by TOFWERK produces ions via a two-step chemical ionization process, which involves 1) producing reagent ions and 2) ionizing neutral analyte molecules via the reagent ions through either charge transfer or adduct formation. Once generated, these secondary ions travel into the SLIM IMS region, where a series of DC- and AC-electrodes on printed circuit boards create a traveling wave driving force. As the ions travel through the helium buffer gas, they separate based on their rotationally averaged collision cross-sections. In the present work, various experiments were performed using an aerosol flow tube reactor and an atmospheric simulation chamber to recreate atmospheric conditions. Gas-phase oxidation of isoprene was used to explore the capabilities of the CI-SLIM IMS-MS under atmospheric relevant conditions. Firstly, the most important oxidation products produced from the OH-oxidation of isoprene were used including methacrolein, methyl vinyl ketone, isoprene epoxy diols (IEPOX), isoprene hydroxy hydroperoxide (1,2 and 4,3-ISOPOOH), and other C5H10O3 reactive uptake products as a single component or as a mixture to first evaluate the capabilities of the CI-SLIM IMS-MS at resolving the different isomers. Secondly, the reactive uptake of IEPOX onto acidic particles and OH-initiated oxidation (low and high NO regimes) of isoprene were studied to characterize the dynamic of the isomers generated within the simulation chamber under various environmental conditions. Results will be presented to demonstrate the capabilities of the newly developed CI-SLIM IMS-MS at resolving isomers in real time. How to cite: Riva, M., Gerber, S., Claflin, M., Mettke, P., Frauenheim, M., Rice, R., Gold, A., Surratt, J., Yatsyna, V., Graf, S., Canagaratna, M., Herrmann, H., Rohner, U., Kamrath, M., and Lopez-Hilfiker, F.: Real-time monitoring of dynamic isomer populations with CI-SLIM IMS-MS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6074,, 2024. 
    more » « less
  5. Abstract Rationale

    Charge transfer dissociation (CTD) is a novel fragmentation technique that demonstrates enhanced structural characterization for a wide variety of molecules compared to standard fragmentation techniques like collision‐induced dissociation (CID). Alternative fragmentation techniques, such as electron transfer dissociation, electron capture dissociation, and ultraviolet photodissociation, also overcome many of the shortfalls of CID, but none of them are a silver bullet that can adequately characterize a wide variety of structures and charge states of target compounds. Given the diversity of structural classes and their occasional obstinance towards certain activation techniques, alternative fragmentation techniques are required that rely on novel or alternative modes of activation.


    Herein, we present a step‐by‐step protocol for the installation of CTD on a quadrupole ion trap mass spectrometer and best practices for optimizing the signal‐to‐noise ratio and acquisition times for CTD mass spectra.


    In addition to two CTD installations in the Jackson laboratory, CTD has also been installed, and is currently in operation, on two 3D ion trap mass spectrometers in France: one in the laboratory of Dr. David Ropartz and Dr. Hélène Rogneaux at INRAE in Nantes, and the other in the laboratory of Dr. Jean‐Yves Salpin at Université d'Évry Val‐d'Essonne, part of the Paris‐Saclay University system.


    Here, we provide a visual protocol to help others accomplish the instrument modification.

    more » « less