A discharge ionization detector (DID) is a type of detector used in
gas chromatograph
Gas chromatography (GC) is a common type of chromatography used in analytical chemistry
Analytical chemistry studies and uses instruments and methods to separate, identify, and quantify matter. In practice, separation, identification or qua ...
y.
Principle
A DID is an
ion detector which uses a high-voltage
electric discharge
An electric discharge is the release and transmission of electricity in an applied electric field through a medium such as a gas (ie., an outgoing flow of electric current through a non-metal medium).American Geophysical Union, National Research ...
to produce
ion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
s. The detector uses an electrical discharge in helium to
generate high energy UV photons and metastable
helium
Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
which ionizes all compounds except helium.
[http://www.cesstech.com.my/data/products/Gas/Gas_Chromatograph_GowMac%20Brochure/Gow-Mac%20590.pdf ] The
ion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...
s produce an
electric current
An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume. The movin ...
, which is the
signal
In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The '' IEEE Transactions on Signal Processing' ...
output of the detector. The greater the concentration of the component, the more ions are produced, and the greater the current.
Application
DIDs are sensitive to a broad range of components.
In Air Separation plants they are used to detect the components CO; CH2; C+; N2; O2 in Argon product in ppm range.
DIDs 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.
DIDs are an improvement over
Helium ionization detector
A helium ionization detector (HID) is a type of detector used in gas chromatography.
Principle
HID connected to a GC has the great advantage to use helium as both the carrier gas and the ionization gas. HID is an ion detector which uses a radioa ...
s in that they contain no
radioactive
Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consi ...
source.
References
Gas chromatography
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