Ion behavior in an electrically compensated ion cyclotron resonance trap

We recently described a new electrically compensated trap in FT ion cyclotron resonance mass spectrometry (J. Am. Soc. Mass Spectrom. 19 (2008) 1281-1285) and developed a means of tuning traps of this general design (J. Am. Soc. Mass Spectrom. 21 (2010) 451-454). Here, we describe a continuation of that research by comparing the ion transient lifetimes and the resulting mass resolving powers and signal-to-noise (S/N) ratios that are achievable in the compensated versus uncompensated modes of this trap. Transient lifetimes are 10 times longer under the same conditions of pressure, providing improved mass resolving power and S/N ratios. The mass resolving power as a function of m/z is linear (log-log plot) and nearly equal to the theoretical maximum. Importantly, the ion cyclotron frequency as a function of ion number decreases linearly in accord with theory, unlike its behavior in the uncompensated mode. This linearity should lead to better control in mass calibration and increased mass accuracy than achievable in the uncompensated mode.