The English used in this article may not be easy for everybody to understand. (June 2012)
Mass spectrometry (MS) is a process that measures the mass-to-charge ratio of charged particles. You can use it to find out the mass of particles, and to find the basic chemicals in a sample or molecule. It can also tell you the chemical structures of molecules, such as peptides and other chemical compounds.
There are 5 main steps a mass spectrometer takes:
- Vaporization: The substance has to be injected into the ionizing tube, where it is turned into a gas if it isn't already one. This is done by heating up the substance so much that it vaporizes, which allows the substance to move along the mass spectrometer.
- Ionization: The sample is then hit with electrons by an electron-gun, changing the sample so it only has positively-charged ions. This is so the samples are attracted to the magnetic fields, allowing the mass spectrometer to work.
- Acceleration: The positively-charged ions are then accelerated through an electric field of negatively charged plates which the ions are attracted to, to allow them to be tested in the next stages.
- Separation: As the ions are moved along a magnetic field, the atoms with a higher mass-to-charge ratio will not be affected as much by the magnetic field, while those with a lower mass-to-charge ratio will be affected more. Most atoms only have a single charge, so with those, the angle of the heavier atoms won't change much, while the angle of the lighter atoms will change a lot. This is because they have more mass compared to their single charge.
- Detection: There is a detector at the end of the mass spectrometer. When an ion hits the detector, a single electric current is produced at that location, which is then multiplied many times so a computer can notice it. The current produced is always proportional to the amount of ions of that specific type hitting the location. Molecules and atoms of the same type will always hit a specific location of their own.
Using the information which the method can collect, you can find the mass-to-charge ratio of the particles, and the relative abundance (how many atoms of each type were in the sample you put in).
The first mass spectroscope was invented by the British physicist J. J. Thomson in 1912. His student Francis Aston developed the mass spectroscope for practical use. They are now widely used for agriculture, brewing, food processing, geology, petroleum exploration, medical drugs measurements and space exploration. They are often used with a chromatography system which helps prepare the sample for mass spectrometry. 
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- Bozeman Science (2013-08-08), Mass Spectrometry, retrieved 2017-08-24
- "Mass Spectrometry". Encyclopedia of 20th Century Technology. 2005. Retrieved 30 July 2011.
- Mass Spectrometry by Paul Andersen on Youtube
- Mass Spectrometry MS by the Royal Society of Chemistry on Youtube