Mass Spectrometer

Mass Spectrometer is an instrument used in measuring masses of various isotopes present in an atom.

In 1919, a chemist, Francis. W. Aston, designed an instrument called a mass Spectrometer for separating ions of different masses.

A beam of positively charged ions was sent through a magnetic field in a Mass Spectrometer. It was observed that the ions did not form a single beam corresponding to the mass of 35.5 which is the relative atomic mass of chlorine. Rather it was divided into two. The stronger beam had a mass of 35 while the weaker beam had a mass of 37.

This shows that chlorine contains two types of atoms mixed in a different proportion to give a relative molecular mass of 35.5.