Helium ionization detector
Encyclopedia
A helium ionization detector (HID) is a type of detector used in gas chromatography.
which uses a radioactive source to produce ion
s. The radioactive source ionizes helium
atoms by bombarding them with emissions. As components elute from the GC's column they are mixed with the helium ions, which then ionize the components. The ion
s produce an electric current
, which is the signal output of the detector. The greater the concentration of the component, the more ions are produced, and the greater the current.
HIDs are non-destructive detectors. They do not destroy/consume the components they detect. Therefore they can be used before other detectors in multiple-detector configurations.
The drawback to HIDs are that they contain a radioactive source. In the U.S., this means they fall under a number of federal regulations concerning their use in the workplace, shipping, disposal, etc. Discharge ionization detector
s have generally supplanted them.
Principle
An HID is an ion detectorGC ion detector
Many GC detectors are ion detectors with varying methods of ionizing the components eluting from the GC's column.-Principle of Operation:An ion detector is analogous to a capacitor or vacuum tube. It can be envisioned as two metal grids separated by air with inverse charges placed on them. An...
which uses a radioactive source to produce ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s. The radioactive source ionizes helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...
atoms by bombarding them with emissions. As components elute from the GC's column they are mixed with the helium ions, which then ionize the components. The ion
Ion
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
s produce an electric current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
, which is the signal output of the detector. The greater the concentration of the component, the more ions are produced, and the greater the current.
Application
HIDs are sensitive to a broad range of components. They must use helium as a carrier gas.HIDs are non-destructive detectors. They do not destroy/consume the components they detect. Therefore they can be used before other detectors in multiple-detector configurations.
The drawback to HIDs are that they contain a radioactive source. In the U.S., this means they fall under a number of federal regulations concerning their use in the workplace, shipping, disposal, etc. Discharge ionization detector
Discharge ionization detector
A discharge ionization detector is a type of detector used in gas chromatography.-Principle:A DID is an ion detector which uses a high-voltage electric discharge to produce ions. The spark ionizes helium atoms that are mixed with components as they elute from the GC's column, causing the...
s have generally supplanted them.