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 spectrom eter. Quadrupolar excitation and collisional axialization are used to move ions located in any region of the ICR cell to the center of the c ell, where they can be effectively detected. With this method, the sig nal from ions formed by a single laser desorption event is averaged fo r 200 remeasurement cycles with an efficiency in excess of 99.5% per c ycle. Collisions of ions with helium are found to give higher remeasur ement efficiencies than collisions with methane, due to reduced scatte ring 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. Thi s technique is shown to be compatible with high-resolution data acquis ition. Ions formed by one laser desorption event are remeasured at eig ht bandwidths, demonstrating low-resolution, wide-mass-range analysis and high-resolution, narrow-mass-range analysis of the same group of i ons.