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Electron capture detectors emit beta particles and gases to detect chemical compounds in samples. They generate a current by scattering electrons and detecting changes in electrical current. Modern detectors use plasma and operate in DC or pulsed mode. They are used in gas chromatography and require careful handling and regulatory compliance. Only authorized professionals may install, test, or remove them, and specific procedures must be followed for disposal.
Used to detect chemical compounds in sample substances, an electron capture detector typically emits radioactive beta particles and gases, such as nitrogen, in a mixture. These particles typically collide with and are carried by gas molecules, while the collisions scatter electrons which then drift towards a positively charged electrode. A current is generated by this process and as the electrons are recaptured, the current between two electrodes decreases. Compounds in the sample are usually detected by the change in electrical current. Invented in the 1950s, the electron capture detector is often used to detect halogens, nitro or nitrile compounds, as well as carbon and metal-related chemicals.
Modern electron capture detectors in the 21st century sometimes use plasma to generate a stream of electrons. Most devices work by applying a constant direct current (DC) potential or a pulsed potential. With DC mode operation, enough voltage is introduced to collect the emitted electrons. A constant current is produced which typically drops as the molecules begin to collide. The change pattern is used to detect compounds.
Pulsed mode operation generally blocks the path of most negatively charged molecules. When the pulse is in off mode, the electrons react with the gas. Materials can be detected through the motion of their particles, which is affected by the timing, frequency and amplitude of the pulses. Nitrogen and halogen are often used in an electron capture detector because relatively few electrons are captured by their atoms. Substances can then more easily capture the free flowing electrons through the system.
Electron capture detectors are often used in gas chromatography and were initially developed for use in that field. Still used in the 21st century, these detectors generally need to be handled with care. Permission from regional authorities is often required to acquire and operate an electron capture detector. Inventory records, manufacturer test results, and a list of specifications sometimes need to be submitted for safety review.
A profession with a permit may be the only person authorized to install, test or remove an electron capture detector. Regulations may also require warning labels to be visible on the device or in the room where it is stored. There are often requirements that flammable substances must not be stored near the detector. Because it typically contains radioactive material, you may also need to follow specific procedures for disposing of the instrument.
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