What is a Mass Spectrometer?

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  • Written By: Michael Anissimov
  • Edited By: Niki Foster
  • Last Modified Date: 22 November 2015
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A mass spectrometer is a device that can be used to determine the chemical composition of a sample with high degrees of accuracy. The enabling techniques were developed early in the 20th century by a number of scientists. The mass spectrometer is put to use many thousands of times each day by researchers in labs and universities worldwide.

The mass spectrometer works based on the principle that different chemicals have different masses. To determine the mass of chemicals in a sample, the sample is first vaporized, then ionized. The result is an ionized gas that is accelerated through a chamber.

Because ionized gases respond to magnetic fields, a magnet on the wall of the chamber is used to bend the ions towards a detector. Lighter ions are bent quickly towards the detector, while heavier ions are bent at a slower rate. The resulting distribution of ions, called a mass spectra, can be used to determine the content of the original sample.


There are many different types of ionization for the mass spectrometer, including electron ionization, chemical ionization, electrospray ionization, matrix-assisted laser desorption/ionization, fast atom bombardment (FAB), thermospray, atmospheric pressure chemical ionization (APCI), secondary ion mass spectrometry (SIMS) and thermal ionisation. Electrospray ionization, which was only developed a couple of decades ago, is particularly useful when the sample is a solid rather than a liquid or gas. When a sample is known to contain a complex mix of chemicals with different molecular weights, such as in biological samples, a more accurate mass spectrometer is needed. In contrast, for samples composed of only a few simple molecules, a more primitive mass spectrometer will work fine.

A mass spectrometer is used with a variety of other approaches to determine the composure of chemicals. It can also be used to detect isotopes. Although the mass spectrometer technique doesn't directly tell you how much of each chemical a sample contains, but merely which chemicals it contains, careful interpretation of mass spectra can give information about chemical ratios.


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