Digital Revitalization of a Legacy Linear Ion Trap System

Linear ion traps offer a wealth of experimental options for tandem MS and provide a platform for conducting foundational ion chemistry experiments. Despite an extensive history of contributions to mass spectrometry fundamentals and applications, the commercial availability of such instruments has decreased from historical highs, and the cost and maintenance of new instrumentation have become increasingly prohibitive. In domains where a broad degree of functionality is ideally paired with low-cost maintenance (e.g., scientific education and experiments not requiring high throughput), few options exist. To address this growing concern in the mass spectrometry community, this work demonstrates a tractable, proof-of-principle approach to digitally revitalize an end-of-life linear quadrupole ion trap. The factory electronics and drivers were removed and replaced with lower-cost and readily available components. The analyzing quadrupole was operated and controlled entirely digitally using the Astraea digital waveform generation platform. The digital driver is largely hardware-agnostic as the waveforms are software-defined (e.g., not resonantly tuned), making it applicable to most quadrupole designs. This work presents an initial characterization of the digitally driven ion trap. The ion trap was able to isotopically resolve singly and doubly charged ions when a low-voltage auxiliary waveform was used in conjunction with the duty cycle during mass scans. The auxiliary waveform can match the secular frequency of any ion in the trap regardless of the AC frequency and voltage. This permitted mass-selective elimination of ions during accumulation or afterward. The tunable auxiliary frequency facilitated activation and fragmentation of a small peptide ion. The duty cycle was used to isolate a fragment as the precursor ion for a second activation step. The second activation step proceeded without altering the AC conditions of the trap.