ISOLATED DUAL TRAPPED ION CELL ASSEMBLY FOR FOURIER-TRANSFORM ION-CYCLOTRON RESONANCE MASS-SPECTROMETRY

An electrically isolated dual trapped ion cell positioned in the strong magnetic field of a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer is demonstrated to overcome an inefficient electron ionization duty cycle that is common to previous dual cell configurations. A repeller grid positioned between differentially pumped trapped ion cells allows continuous ion formation to occur in the source while excluding electrons from the analyzer cell during concurrent data acquisition. In a systematic study of dual cell performance including transfer efficiency, mass selectivity, and signal enhancement, the high-field isolated dual cell design was compared to conventional dual cell and fringing field external cell arrangements. Several ion trapping and manipulation schemes were investigated. For the high-field isolated cell, gated transfer and equillbrium pulse sequence transfer efficiencies routinely exceeded 80% and 30%, respectively. These values were similar to the performance achieved with the conventional dual cell design. In contrast, transfer efficiencies for the fringing field source were a factor of 5 poorer. However, when time-of-flight-based mas selection was desired, superior performance was derived from the fringing field source because of increased path length. Finally, large ionization duty cycle increases were achieved for continuous beam experiments in the isolated dual cell with consequent S/N improvements as high as a factor of 30 compared to the conventional dual cell in otherwise identical high-resolution measurements.