Electron ionization

Electron ionization (also called electron impact ionization) is a common method used in mass spectrometry, especially for studying small and stable molecules that can become gas. In this method, a beam of high-energy electrons is shot at gas molecules in the sample. These electrons knock out other electrons from the molecules, turning them into positively charged ions. These ions are then studied based on their mass and charge, which helps create a pattern called a mass spectrum. Electron ionization is known as a “hard” ionization method because it gives the molecules enough energy not only to charge them, but also to break them into pieces. These pieces give scientists helpful clues about what the molecule is made of.^[1]

Electron ionization

Electron ionization is one of the oldest and most important methods used in mass spectrometry. It still plays a big role in science today. The process happens inside a vacuum chamber in the mass spectrometer. The sample is turned into a gas and then hit with a beam of high-energy electrons. These electrons knock one electron off the sample molecules, creating charged particles called molecular ions. These ions often break into smaller pieces. The pattern of these pieces is like a molecular fingerprint. Scientists can use this pattern to figure out the structure of the molecule and compare it to known samples in a database to identify the substance.^[1]

Electron ionization (EI) is most often used in gas chromatography–mass spectrometry (GC-MS). It is the standard method because it gives repeatable results and has a large collection of reference data. EI works especially well for studying organic compounds like oils (hydrocarbons), alcohols, esters, ketones, and amines. Because it breaks molecules in predictable ways, it is great for finding out what’s in a sample and how much is there. Scientists use EI in many areas, like crime labs, environmental testing, medicine, food safety, and studying fuels and chemicals.^[2]

Even though electron ionization (EI) has many benefits, it also has some limitations. It only works well with substances that can be turned into a gas and stay stable when heated. If a compound is not easy to vaporize, breaks down with heat, or is very polar, EI may not work well. In these cases, scientists use other gentler methods, like electrospray ionization (ESI) or chemical ionization (CI). Also, because electron ionization breaks the molecules into many smaller pieces, the main piece, called the molecular ion, can be very weak or sometimes not seen at all in the results. This can make it harder to figure out the full size or weight of the original molecule, which is important when trying to identify what the substance is.^[2][3][4]

Even with its limits, electron ionization (EI) is still one of the most important tools in mass spectrometry. It is simple to use, very reliable, and gives a lot of useful information about the molecules being tested. One of its biggest strengths is how it breaks molecules in predictable ways, which helps scientists figure out what the substance is and what it is made of. Because scientists have collected so many examples of these patterns in big databases like the NIST Mass Spectral Library, EI is now one of the best and most trusted methods for studying small organic molecules.^[5]