rf capacitive coupling with efficient gated trapping in internal matrix-assisted laser desorption ionization Fourier transform ion cyclotron resonance

A method to combine gated trapping and capacitive coupling into a single experiment is reported. This is achieved with a circuit that allows isolation of the electronic network that gates the trapping voltage from the circuit that enables capacitive coupling of the rf excitation signal to the trapping plates. When the capacitive coupling network is not isolated from the gated trapping network, the trapping voltage changes occur on a 100 mu s or longer timescale, which is incompatible with efficient capture of ions formed by matrix-assisted laser desorption ionization. Isolation of the two networks allows the trapping voltage to be gated with less than a 10 mu s risetime. The effectiveness of this approach is demonstrated by a set of experiments carried out with and without the benefit of the isolation of capacitive coupling from gated trapping. (C) 1997 American Society for Mass Spectrometry