Voltage-induced frequency drift correction in fourier transform electrostatic linear ion trap mass spectrometry using mirror-switching

- Mirror-switching is used to capture externally injected ions in an electrostatic linear ion trap.
- Frequency shifts that are experimentally observed in an electrostatic linear ion trap were characterized and reduced.
- The shifts arise from ion capture via mirror-switching and the power supplies transient voltage recovery.
- The effect was minimized by superimposing the inverted voltage recovery onto the electric field of the opposing reflectron.
- Pressure/noise-limited theoretical resolutions are demonstrated for the model compounds.

Ion capture from an external nano-electrospray ionization source in a Fourier transform electrostatic linear ion trap has been effected by mirror-switching. This capture method can suffer from time-dependent frequency shifts in the measured ion motion, which compromises mass resolution when using Fourier transform techniques for mass determination. This phenomenon was determined to be a result of the transient voltage recovery of the power supplies used for mirror-switching in response to a pulsed capacitive load, for which several examples are shown. A circuit, based on the AD210AN isolation amplifier, was fabricated to compensate for the voltage perturbation induced by mirror-switching by superimposing the inverted perturbation to the electric field of the opposing reflectron. In doing so, the dependence of the ions path length and frequency on the power supply output was greatly reduced throughout data acquisition. With this circuit enabled, no frequency shifts were observed in the mass spectrum when using mirror-switching, and thus pressure-limited theoretical resolutions were achieved. For example, an absorption mode resolving power of greater than 50,000 M/ΔM FWHM was observed for iodide (m/z 126.9) at a transient length of 300 milliseconds. The use of mirror-switching led to a much greater m/z range than in-trap potential lift for a single ion injection which is demonstrated via simulation and experimental results. This correction method is simple to implement and does not require user intervention once properly tuned.

131