Learning Idea

Determination of Atomic masses by mass spectrometry An instrument that measures the exact masses of different isotopes of an element is called a mass spectrometer and this technique is called mass spectrometry. First of all Aston’s mass spectrometer was used to identify the isotopes of an element. The Dempster’s mass spectrometer is used to identify isotopes of solid elements. The principle of the mass spectrometer is that the positive ion of each isotope has its own (m/e) value. The isotopes are separated based on their mass-to-charge ratio (m/e). Construction and Working: The substance (isotopic element) under analysis is converted into vapuors and is kept very low (10 -6 to 10-7 torr). These vapours enter an ionization chamber. Here fast-moving electrons collide with vapours. Thus vapours are ionized. Different isotopes produce different ions with different (m/e) values. These positive ions are accelerated by applying a potential difference of 500-200 volts to the perfora...