Characterization of the ion beam focusing in a mass spectrometer using an IonCCD™ detector.

A position sensitive pixel-based detector array, referred to as the IonCCD, has been employed to characterize the ion optics and ion beam focusing in a custom built mass spectrometer designed for soft and reactive landing of mass-selected ions onto surfaces. The IonCCD was placed at several stages along the path of the ion beam to determine the focusing capabilities of the various ion optics, which include an electrodynamic ion funnel, two radiofrequency (rf)-only collision quadrupoles, a mass resolving quadrupole, a quadrupole bender, and two einzel lens assemblies. The focusing capabilities of the rf-only collision quadrupoles and einzel lenses are demonstrated by large decreases in the diameter of the ion beam. In contrast, the mass resolving quadrupole is shown to significantly defocus the mass-selected ion beam resulting in an expansion of the measured ion beam diameter. Combined with SIMION simulations, we demonstrate that the IonCCD can identify minor errors in the alignment of charged-particle optics that result in erratic trajectories and significant deflections of the ion beam. This information may be used to facilitate the design, assembly, and maintenance of custom-built mass spectrometry instrumentation.