Simultaneous positive and negative HRAM acquisition using a Q-TOF mass spectrometer with ultra-high mass stability

Importance of the topic

The ability to acquire high-resolution accurate-mass (HRAM) data in both positive and negative ion modes within a single run greatly enhances the throughput and versatility of LC–MS workflows. By reducing the time penalty associated with polarity switching, laboratories can analyze complex samples more efficiently, maintaining low-ppm mass accuracy under typical operating conditions.

Goals and overview of the study

This study aimed to develop and validate a novel conversion algorithm that compensates for voltage instability during rapid polarity switching on a quadrupole time-of-flight (Q-TOF) system. Using a prototype Shimadzu LCMS-9050 instrument, researchers demonstrated that a 600 ms switching interval, combined with the new correction formula, yields consistent low-ppm mass errors in both ionization modes.

Methodology and used instrumentation

Researchers employed a Q-TOF mass spectrometer (Shimadzu LCMS-9050 prototype) configured for alternating positive and negative ion detection. The core of the approach is a refined time-of-flight (TOF) to m/z conversion equation: the basic form (Equation A) relates flight time to m/z under constant voltage assumptions, while the enhanced form (Equation B) introduces a correction term as a function of the elapsed time after polarity switching and the acquisition time. Key experimental steps:

• Measure TOF for sodium iodide cluster ions in both modes.
• Determine mass error trends over subsecond intervals post-switching.
• Optimize correction parameters to minimize mass shifts.
• Verify long-term mass stability using an antibiotic reference standard mix (150–1100 Da).

Main results and discussion

Initial tests using the uncorrected algorithm revealed a transient mass deviation lasting up to one second after switching. Applying the time-dependent correction term reduced these shifts to under 1 ppm in positive mode (e.g., [NaI]6Na+ error ~ –0.6 ppm) and about 2–3 ppm in negative mode. Long-term measurements at room temperature showed stable mass accuracy within ±3 ppm across a range of compounds, confirming the robustness of the correction under typical laboratory conditions.

Benefits and practical application

By enabling simultaneous acquisition of positive and negative ions with minimal mass error, this method:

• Increases sample throughput by eliminating prolonged stabilization delays.
• Maintains high mass accuracy across both modes in a single analytical run.
• Supports comprehensive profiling in metabolomics, proteomics, and environmental analyses.

Future trends and potential uses

Anticipated developments include:

• Integration with ultra-fast chromatography for high-throughput screening.
• Real-time feedback loops to adapt correction parameters dynamically.
• Expanded use in regulated QA/QC environments requiring dual-mode confirmation.
• Application to emerging ionization techniques that demand rapid polarity alternation.

Conclusion

The introduced correction algorithm effectively compensates for high-voltage instability, achieving low-ppm mass accuracy with a rapid 600 ms polarity switch on the Q-TOF platform. The Shimadzu LCMS-9050 thus offers a practical solution for simultaneous dual-polarity analysis, enhancing analytical throughput without sacrificing data quality.