velocity-focusing spectrometer

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July 14, 2026

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A velocity-focusing spectrometer is a type of mass spectrometer that brings ions of a specific mass to a focus, regardless of their velocity. This is achieved by arranging successive electric and magnetic fields in a specific way. This design, developed by Francis W. Aston, allows for accurate measurement of isotope masses.1

In contrast, Dempster's spectrometer used only a magnetic field to focus ion beams of a specific mass and energy that diverged from a slit. These instruments are crucial for separating ions based on their mass-to-charge ratio, a fundamental principle in mass spectrometry.123

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mass spectrometry
Focusing spectroscopes
…to what is known as velocity focusing. Aston’s design was the basis of his later instruments with which he systematically and accurately measured the masses of the isotopes of many of the elements. He chose ¹⁶O (the isotope of oxygen of mass 16) as his standard of mass.
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…to what is known as velocity focusing. Aston’s design was the basis of his later instruments with which he systematically and accurately measured the masses of the isotopes of many of the elements. He chose ¹⁶O (the isotope of oxygen of mass 16) as his standard of mass.
Read More