A tuning method for electrically compensated ion cyclotron resonance mass spectrometer traps.

We describe a method for tuning electrically compensated ion cyclotron resonance (ICR) traps by tracking the observed cyclotron frequency of an ion cloud at different oscillation mode amplitudes. Although we have used this method to tune the compensation voltages of a custom-built electrically compensated trap, the approach is applicable to other designs that incorporate electrical compensation. To evaluate the effectiveness of tuning, we examined the frequency shift as a function of cyclotron orbit size at different z-mode oscillation amplitudes. The cyclotron frequencies varied initially by approximately 12 ppm for ions with low z-mode oscillation amplitudes compared with those with high z-mode amplitudes. This frequency difference decreased to approximately 1 ppm by one iteration of trap tuning. Copyright 2010. Published by Elsevier Inc.