Duty cycle-based isolation in linear quadrupole ion traps

Simulation and matrix methods were used to determine the change in the minimum trapping frequency during duty cycle base waveform manipulation to provide axial trapping. Duty cycle based axial trapping sets both rod sets of a digitally driven linear quadrupole to the same potential thereby nullifying the radial trapping field for a definable interval during the waveform cycle. Turning off the radial trapping field affects the ion motion. Consequently, the ion stability conditions and the secular frequency change with duty cycle during axial trapping. The work presented here demonstrates the change in the ion motion by simulating the ion trajectories under duty cycle base trapping conditions and determining the change in the minimum trapping frequency as a function of the change in duty cycle. The change in the stability conditions with duty cycle was determined by matrix methods. These calculations were used to determine the minimum trapping frequency change with duty cycle and validate the simulations. They were then used to discuss the duty cycle effects and propose methodology for using duty cycle waveform manipulation to perform precise ion isolation. Finally, matrix methods were used to show that ion isolation can be performed concurrently with duty cycle based axial trapping. These results were confirmed by simulation.