Beyond the Limits of Conventional Mass Spectrometry with Superconductivity

Abstract

Superconducting tunnel junction (STJ) detectors for ions and neutral molecules have the ability to overcome the limits of conventional mass spectrometry, utilizing the performance of kinetic energy measurement of individual atoms and molecules in an energy range of 100 eV–100 keV. This unusual performance is realized by a small superconducting energy gap of ～meV, which is lower than the energies of phonons that are the quanta of crystal lattice vibration. The superconducting detectors are sensitive to molecule impact on the surface of superconductors through lattice vibration generation instead of using secondary electron emission that is used in conventional molecule detectors. An output pulse height is determined by the energy deposited to the detector surface, which is proportional to the product of charge number and acceleration voltage (zV [eV]). Consequently, it is possible to simultaneously determine m/z and z values of individual ions in vacuum, which is an advantage over ion mobility mass spectrometry (IMS) in a drift gas or charge detection mass spectrometry (CDMS). The STJ detectors can overcome the two fundamental MS limits of “m/z overlap” in different charge states and “neutral loss” in tandem mass spectrometry. For example, no one has identified doubly-charged homonuclear diatomic molecular ions of ¹⁴N₂²⁺ before us. In this paper, we report the experimental results obtained by using double-focused-MS, MALDI-TOF-MS, and ESI-TOF-MS equipped with a STJ detector. The superconducting detectors are expected to be employed in space and in electrostatic ion storage rings for planetary science, interstellar chemistry (origin of life), atomic and molecular sciences, and life sciences.