Matrix-shimmed ion cyclotron resonance ion trap simultaneously optimized for excitation, detection, quadrupolar axialization, and trapping

A different symmetry is required to optimize each of the three most common Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) ele ctric potentials in a Penning (ICR) ion trap: one-dimensional dipolar ac fo r excitation (or detection), two-dimensional azimuthal quadrupolar ac excit ation for ion axialization, and three-dimensional axial quadrupolar de pote ntial for ion axial confinement (trapping). Since no single trap shape simu ltaneously optimizes all three potentials, many trap configurations have be en proposed to optimize the tradeoffs between the three requirements for a particular experiment. A more general approach is to divide each electrode into small segments and then apply the appropriate potential to each segmen t. Here, we extend segmentation to its logical extreme, by constructing a " matrix-shimmed" trap consisting of a cubic trap, with each side divided int o a 5 x 5 grid of electrodes for a total of 150 electrodes. Theoretically, only 48 independent voltages need be applied to these 150 electrodes to gen erate all three desired electric potential fields simultaneously. In practi ce, it is more convenient to employ 63 independent voltages due to construc tion constraints. Resistive networks generate the potentials required for o ptimal quadrupolar trapping and quadrupolar excitation. To avoid resistive loss of excitation amplitude and detected signal, dipolar excitation/detect ion voltages are generated with a capacitive network. Theoretical Simion 6. 0 simulations confirm the achievement of near-ideal potentials of all three types simultaneously. From a proof-of-principle working model, several exp erimental benefits are demonstrated, and proposed future improvements are d iscussed. (C) 1999 American Society for Mass Spectrometry.