ANALYSIS OF HARMONICS FOR AN ELONGATED FTMS CELL WITH MULTIPLE ELECTRODE DETECTION

The form of FTMS signals is analyzed for the general case of multiple electrode ICR cells with detailed results for two, eight and sixteen e lectrodes. The analysis is based on an elongated cylindrical cell to r educe the problem of treating the electric field distribution to two d imensions. The relative contributions of cyclotron and magnetron motio n to the detected signal are analyzed for multiple electrode detection to establish the conditions for maximizing high order harmonic detect ion as a strategy for simultaneously enhancing mass resolution and sen sitivity for characterizing high mass ions in FTMS. For pure cyclotron motion (no magnetron motion) only the basic frequency and its odd har monics are detected by two electrodes; for multiple electrodes the tra nsformed frequencies (originating from the commutation effect) and the ir odd harmonics are detected. The relative intensities of harmonic si gnals are greatly enhanced in large orbits, which also maximize the si gnal strength. Good agreement between the modeled FTMS signal and expe rimental results for a sixteen electrode ICR cell is demonstrated. The general conclusion is that minimization of magnetron motion is requir ed for simplification and optimization of the FTMS signal with multipl e electrode detection. This is entirely feasible with current technolo gy and is a useful strategy for significantly enhancing mass resolutio n and S/N ratio in FTMS.