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How did mass spectrometry help identify neon-22 as an isotope of neon?

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Mass spectrometry played a pivotal role in identifying neon-22 by allowing scientists to separate and detect gaseous ions based on their mass-to-charge ratios.1

In early experiments using a parabola spectrograph, J.J. Thomson observed that neon produced two distinct positive rays. While one ray corresponded to the expected mass of 20, a second line appeared at mass 22 that could not be attributed to any known gas. Because this substance could not be separated from neon by chemical means, it was identified as a stable heavy isotope of neon.23

To confirm this discovery, Francis William Aston developed a more precise mass spectrograph by 1919. His instrument provided the necessary accuracy to distinguish the heavier neon-22 ions from the lighter neon-20 ions, convincingly proving that both were forms of the same element. This technique of sorting ions in electric and magnetic fields remains a fundamental method for identifying isotopes and determining their relative abundances.21