Mass spectrometry

Mass spectrometry (MS) is a science tool used to find out what things are made of by measuring mass and charge of tiny particles called ions.^[1] This helps scientists identify, measure, and even understand the structure of different chemical substances. Mass spectrometry is very powerful and useful in many areas of science. It can tell researchers the molecular weight (how heavy a molecule is), separate complicated mixtures, and give clues about how molecules are put together. Scientists use it to study materials from living things, the environment, and factories.^[2]

A basic mass spectrometer. This one shows the measurement of isotopes in carbon dioxide.

A modern mass spectrometer

A mass spectrometer works in five main steps:^[2][3][4]

1. Vaporization: The substance is first injected into a special tube, where it is heated until it turns into a gas (if it is not a gas already). This step is important because the mass spectrometer can only work with gases.
2. Ionization: The gas particles are then hit with a beam of electrons from an electron gun. This knocks off electrons from the particles, turning them into positively charged ions. Only charged particles can be moved and controlled by electric and magnetic fields.
3. Acceleration: These ions are pushed through an electric field made by negatively charged plates. Since opposites attract, the positive ions speed up toward the plates. This gives them the energy needed for the next stage.
4. Separation: The ions enter a magnetic field, which bends their paths. Lighter ions (with a lower mass-to-charge ratio) are bent more, and heavier ions are bent less. This causes the ions to spread out based on their size and charge.
5. Detection: At the end, a detector catches the ions. When an ion hits the detector, it creates a tiny electric signal. The more ions of a certain type that hit the detector, the stronger the signal. A computer records this data and makes a graph showing what kinds of ions were in the sample and how much of each was present.

There are different kinds of mass analyzers, like quadrupole, time-of-flight (TOF), ion trap, orbitrap, and FT-ICR, each using different ways to separate and measure the ions.^[2]

Mass spectrometry is very good at detecting even tiny amounts of substances. It can find extremely small amounts down to the level of femtomoles or attomoles, which are amounts way too small to see. It works on many kinds of substances, from small chemicals to large molecules like proteins, DNA, and fats. A special type called tandem mass spectrometry (MS/MS) breaks the ions into smaller pieces and analyzes them again. This helps scientists learn more about the structure of molecules, such as the order of building blocks in a protein or changes made to a protein after it is made. Mass spectrometry is often combined with other methods like gas chromatography (GC-MS) or liquid chromatography (LC-MS). These help separate the parts of a mixture before analyzing them. This makes it easier to study complex samples, and it is used in areas like drug testing, pollution studies, and researching how the body uses chemicals.^[2]

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.^[5] Mass spectrometry is a powerful tool used in many areas of science. In farming, it helps check for leftover pesticides, study nutrients in soil, and watch how healthy crops are. In food and drink production, like brewing and food factories, it helps make sure the flavor is right and there are no harmful chemicals or unwanted ingredients. In geology, scientists use it to figure out how old rocks and minerals are and to study what Earth is made of. In oil exploration, it helps check what's in crude oil and gives clues about where to drill. In medicine, it helps scientists measure how much medicine is in the body, how it is broken down, and find signs of diseases. Even in space exploration, mass spectrometers are used on spacecraft to study the air, dust, and surfaces of other planets, helping us learn more about our solar system. They are often used with a chromatography system which helps prepare the sample for mass spectrometry.^[2][5][6]