Calibration procedure for secular frequency scanning in ion trap mass spectrometers

Area of Science:

• Analytical Chemistry
• Mass Spectrometry

Background:

• Ion traps can record mass spectra by scanning alternating current (ac) signal frequencies, simplifying instrumentation compared to radiofrequency (rf) amplitude scans.
• Mass calibration presents a significant challenge in this technique.

Purpose of the Study:

• To investigate an algorithm for mass calibration in ion trap mass spectrometry using secular frequency scans.
• To discuss factors influencing ion mass assignments.

Main Methods:

• Time domain data from a linear ion trap mass spectrometer were converted to the m/z domain using ion Mathieu parameter q_u values.
• An algorithm derived from Mathieu equations was developed to determine q_u, m/z values, and peak widths through successive approximations.
• Experiments involved sweeping an auxiliary ac signal frequency to induce mass-selective ion ejection.

Main Results:

• The developed algorithm achieved calibration accuracy better than 0.1%.
• Mass resolution ranged from 250 to 500 (m/z 100-1800) in secular frequency scans.
• The algorithm's predictions were validated against experimental data.

Conclusions:

• A simple and effective mass calibration method for secular frequency scans in ion traps was successfully implemented.
• The study analyzed the impact of rf amplitude, scan rate, and ac amplitude on calibration.
• Accurate calibration requires corrections for ion mass differences, which are easily integrated into the procedure.