Repurposing a Q-ToF Collision Cell into a Stacked-Ring Ion Trap for Controlled Ion–Molecule Reactions with Minimal Heating

Ion-molecule reactions at near-ambient temperatures provide a controlled means to study gas-phase interactions that underpin fundamental chemical processes, such as binding, molecular recognition, and reactivity. Here, we demonstrate that such experiments can be performed on a commercially manufactured quadrupole time-of-flight mass spectrometer (Q-ToF MS) by electronically reconfiguring the collision cell into a stacked-ring ion trap (SRIT), without mechanical modification. Ten different test ions were successfully stored, including singly charged ions with m/z values from 59 to 556, each demonstrating stable confinement for at least 2 s. The 7+ charge state of lysozyme formed from a neutral aqueous solution (m/z 1788) was also stably confined, highlighting the wide mass range over which reliable trapping is achieved. A proton-transfer reaction was also performed in SRIT using isolated cytochrome c 16+ (m/z 773). The resulting product ions, including cytochrome c 15+ (m/z 825) and protonated dimethylacetamide (m/z 88), were simultaneously observed. Unlike when using a linear ion trap mass spectrometer, both the high-m/z and low-m/z products of the ion-molecule reaction can be detected directly from a single isolated precursor ion. To assess collisional heating, the para-methoxybenzylammonium ion, which has a labile C-N bond with a dissociation energy of 105.8 kJ mol-1, was stored for 2 s, and no detectable fragmentation was observed. Ion temperatures remained close to room temperature and increased only slightly from 292.2 ± 3.2 K to 303.2 ± 3.5 K as the RF peak-to-peak amplitude was raised from 17 to 75 V, corresponding to a typical range required for effective trapping across different m/z values under these conditions. Repurposing the collision cell into a SRIT provides a straightforward approach for studying spontaneous ion-molecule reactions under near-ambient conditions on commercial Q-ToF MS instruments. It is anticipated to be useful for fundamental investigations of gas-phase ion chemistry and for analytical applications, such as selective ion-molecule tagging, structural isomer discrimination, and diagnostic adduct formation.