Working Principle of Mass Spectrometer (MS)

The technique of mass spectrometer is applicable in identifying unknown compounds by mass of the compound or their fragments. The stages within mass spectrometer are
1. Production of ions from sample
2. Separation of ions with different masses
3. Detection of number of ions of each  mass produced
4. Collection of data to generate mass spectrum


Different chemicals have different masses and this fact is used in mass spectrometer to determine what chemicals are present in a sample. The underlying principle of all mass spectrometers is that the paths of gas ions in electric and magnetic field are dependent on their mass to charge ratio (m/z) which is used by analyzer to distinguish ions from one another.

For example, table salt (NaCl) may be vaporized (turned into gas) and ionized (broken down) into electrically charged particles Na+ and Cl – called ions. An electric field accelerates the ions to a high speed. After this, they are directed into a magnetic field which applies a force to each ion perpendicular to the plane defined by the particles’ direction of travel and magnetic field lines. This force deflects the ions to varying degrees depending on their mass to charge (m/z) ratio. Lighter ions get deflected more than heavier ions. The deflector measures deflection of each resulting ion beam. From this measurement, m/z ratio of all ions produced from source can be determined. Every ions have their unique m/z ratio. This way, every ions can be detected on basis of their mass to charge ratio.