Tapered or tilted electrodes to allow the superposition of independently controllable DC field gradients to RF fields

摘要

The present invention is embodied in a method and apparatus for transporting ions via a path generated by RF electrodes having a controllable DC field gradient generated thereon which does not suffer from mass discrimination. In a preferred embodiment, the number of electrodes are doubled to thereby use symmetry to cancel an undesirable DC quadrapole field. By eliminating the DC quadrapole field, the passband of the DC field gradient is increased, allowing for ions of higher mass to be transported. The electrodes are either tilted or tapered to thereby generate the desirable DC field gradient. Tilting and/or tapering the electrodes advantageously modifies the DC field gradient to increase the high ion mass cut-off.