Superconducting tunnel junction (STJ) detectors for ion-charge-number sensitive mass spectrometry

Mass spectrometry (MS) is one of the indispensable methods in analytical chemistry. Conventional ion detectors installed in MS instruments solely count individual keV ions or measure ion flux, which leads to no information on the charge states of the individual ions. Superconducting tunnel junction (STJ) detectors, on the other hand, have sensitivity to the ion-charge-number through kinetic energy measurement of keV ions. The STJ detectors overcome such limits in conventional MS instruments as mass/charge-number (m/z) overlap that occurs between, for example, ¹⁴N⁺ and ¹⁴N₂²⁺ (m/z 14), and neutral loss that means that neutral fragments produced from a precursor ion cannot be analyzed directly in tandem mass spectrometry.