where V 0 (~350 V) and F RF (10 to 60 kHz) are the amplitude and frequency of the trapping potential, and z 0 is the trap axial dimension. We measure F z by a resonant excitation method, in which a weak AC potential is applied to the last ion lens before the trap, penetrating into the trap center along the trap axis. trapping of multiple NPs is rare. Once Q/M is known, the trapping conditions can be adjusted, if necessary, to ensure that the NP will remain stably trapped over the course of a reaction experiment, during which M and Q may both change significantly. Trapping conditions are generally adjusted by adjusting F RF , leaving V 0 fixed near 350 V. If unusually large changes in Q/M occur during reactions, additional adjustments to F RF can be made to maintain stable trapping.