A mass spectrograph is an instrument used to analyze the constituents of substances. It not only detects different kinds of atoms and molecules present in the substance, but also finds out their relative amounts. By the use of electric and magnetic fields, it separates ions of different masses. Do you know how this instrument works?
The working of the mass spectrograph first involves the change of the substance into a gas, which is passed into a vacuum chamber. A beam of electrons is bombarded to change the gas atoms and molecules into ions. The ions are then accelerated, by passing them through an electric field. Then the ions are passed through a magnetic field, where they get deflected. The positive ions are deflected one way, and the negative ions in the opposite direction. The amount of deflection is inversely proportional to the masses of the ions. The heavier the mass, the lesser the deflection. This separates ions of different masses. Ions of the same mass and charge stay together. The ions are then allowed to fall on a photographic plate. Different ions hit the plate at different places and as a result, this photographic plate records the amounts of various atoms and molecules. Photographic plate is used to identify different ions which have hit it. From the intensity variations on the plate, we can know the relative amounts of atoms or molecules present in the substance.
The mass spectrograph was developed by a British scientist, William Francis Aston. He was awarded the Nobel Prize in 1922 for this invention. After this, several other mass spectrographs were developed by many leading scientists like Dempster, Bainbridge, Nier, etc but all were just modifications of Aston’s mass spectrograph.
The mass spectrograph is widely used in geology, chemistry, biology and nuclear physics. It is a very useful instrument for isotopic studies. Aston himself discovered 212 of the 287 naturally occurring isotopes. Mass spectrographs are also used as vacuum leak detectors.