Theoretical Study Synchronized Reverse Scan Collision-Induced Dissociation in Digital Linear Ion Trap

The effectiveness of collision-induced dissociation (CID) in ion trap mass spectrometry (ITMS) is limited by a low-mass cutoff and weak fragmentation yields. Theoretically, the q value is optimized to balance the fractional product ion mass range with adequate energy deposition to improve fragment ion detection in the CID process; however, many promising technologies still depend on the traditional sinusoidal waveform-driven IT. Additionally, traditional CID-based multistage mass spectrometry (MSⁿ) experiments on ITMS rely on complex and time-consuming "tuning" to optimize CID for a particular ion. The digital ion trap (DIT) has a very promising application field in MSⁿ analysis, because of its many unique features. Herein, we conducted a theoretical and experimental investigation of a developed synchronized reverse scan-CID (SRS-CID) using a digital linear ion trap. Specifically, (1) simulations and experiments demonstrated that in the SRS-CID, ions were sequentially scanned from high to low m/z value via the resonance excitation point (q_excitation), producing multiple fragment ions without the need to know the m/z value or complex radiofrequency (rf) tuning of each product ion. The simulations demonstrated that the heating rate in the SRS-CID could reach 0.022 eV/μs. The experiments demonstrated that the optimal reverse scan speed was -0.053 ns/step. (2) We preliminary increased the period by a fixed value (T_step) to control q_excitation to study the molecule fragmentation approach. Different mass spectra were obtained by controlling t_excitation with a fixed T_step. (3) This paper introduces the phase space method to study the motion trajectories of precursor ions and daughter ions. The calculations used and the entire program were uploaded to GitHub. (4) Changing the duty cycle to advantageously shift q_excitation improved the heating rate (0.033 eV/μs) in SRS-CID. Overall, we demonstrated the effectiveness of the developed SRS-CID technique in fragment ion analysis via theoretical derivation, simulation, and experimentation. Furthermore, DIT mass spectrometry was advantageous in tandem mass spectrometry analysis by facilitating modulation of the driving rf period.