REMEASUREMENT OF IONS USING QUADRUPOLAR EXCITATION FOURIER-TRANSFORM ION-CYCLOTRON RESONANCE SPECTROMETRY

Ions formed by a single laser desorption event can be remeasured more than 500 times in a Fourier transform ion cyclotron resonance spectrometer. Quadrupolar excitation and collisional axialization are used to move ions located in any region of the ICR cell to the center of the cell, where they can be effectively detected. With this method, the signal from ions formed by a single laser desorption event is averaged for 200 remeasurement cycles with an efficiency in excess of 99.5% per cycle. Collisions of ions with helium are found to give higher remeasurement efficiencies than collisions with methane, due to reduced scattering losses by the lighter collision gas. With this method, ions that are stored in the analyzer cell for more than 1 h can be detected. This technique is shown to be compatible with high-resolution data acquisition. Ions formed by one laser desorption event are remeasured at eight bandwidths, demonstrating low-resolution, wide-mass-range analysis and high-resolution, narrow-mass-range analysis of the same group of ions.