The mass spectrometer determines chemical composition by ionizing and accelerating a sample through a chamber with a magnet that bends ions towards a detector. Different types of ionization are used, and the technique can detect isotopes and provide insight into chemical ratios.
A mass spectrometer is a device that can be used to determine the chemical composition of a sample with high degrees of accuracy. Enabling techniques were developed in the early 20th century by a number of scientists. The mass spectrometer is used many thousands of times every day by researchers in laboratories and universities around the world.
The mass spectrometer works 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 chamber wall is used to bend the ions towards a detector. Lighter ions are bent rapidly towards the detector, while heavier ions are bent at a slower rate. The resulting distribution of ions, called the 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, rapid atomic bombardment (FAB), thermospray, atmospheric pressure chemical ionization (APCI), mass secondary ion spectrometry (SIMS) and thermal ionization. Electrospray ionization, which was developed just 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 mixture of chemicals with different molecular weights, such as in biological samples, a more accurate mass spectrometer is needed. Conversely, for samples composed of only a few simple molecules, a more primitive mass spectrometer will work well.
A mass spectrometer is used with a variety of other approaches to determining the composition of chemicals. It can also be used to detect isotopes. While the mass spectrometer technique doesn’t directly tell you how much of each chemical a sample contains, just what chemicals it contains, careful interpretation of mass spectra can provide insight into chemical ratios.
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