HIGH-RESOLUTION ION ISOLATION WITH THE ION-CYCLOTRON RESONANCE CAPACITIVELY COUPLED OPEN CELL

For ion cyclotron resonance, a capacitively coupled open cell variant with fourfold radial symmetry was constructed and tested for axial exc itation-ejection of large ions at high resolution. With a reverse of f requency sweep direction, this cell gave substantial improvements in s ignal-to-noise ratio due to linearization of the excitation electric f ield. Single isotopic peaks of ubiquitin (8.6-kDa) and carbonic anhydr ase (29-kDa) molecular ions could be isolated by selective stored wave form inverse Fourier transform excitation, which yielded an order of m agnitude higher isolation resolving power than previously achieved at high mass-to-charge ratio values.