GC ion detector
Encyclopedia
Many GC detectors are ion
detectors with varying methods of ionizing the components eluting from the GC's column.
or vacuum tube
. It can be envisioned as two metal grids separated by air with inverse charges placed on them. An electric potential difference (voltage)
exist between the two grids. After components are ionized in the detector, they enter the region between the two grids, causing current to pass from one to the other. This current is amplified and is the signal generated by the detector. The higher the concentration of the component, the more ions are generated, and the greater the current.
Some early FIDs actually used two metal grids as their ion detectors. However, more efficient designs have been developed, so few current ion-type detectors use two metal grids. But the principle is the same, and it can be easiest to think of the detector in this manner.
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...
detectors with varying methods of ionizing the components eluting from the GC's column.
Principle of Operation
An ion detector is analogous to a capacitorCapacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
or vacuum tube
Vacuum tube
In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
. It can be envisioned as two metal grids separated by air with inverse charges placed on them. An electric potential difference (voltage)
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
exist between the two grids. After components are ionized in the detector, they enter the region between the two grids, causing current to pass from one to the other. This current is amplified and is the signal generated by the detector. The higher the concentration of the component, the more ions are generated, and the greater the current.
Some early FIDs actually used two metal grids as their ion detectors. However, more efficient designs have been developed, so few current ion-type detectors use two metal grids. But the principle is the same, and it can be easiest to think of the detector in this manner.
Types of Ion Detectors
- Flame ionization detectorFlame ionization detectorA flame ionization detector is a type of gas detector used in gas chromatography. The first flame ionization detector was developed in 1957 by scientists working for the CSIRO in Melbourne, Australia....
(FID) -- uses a flame to produce ions - Electron capture detectorElectron capture detectorAn electron capture detector is a device for detecting atoms and molecules in a gas through the attachment of electrons via electron capture ionization. The device was invented in 1957 by Dr. James E...
(ECD) -- uses bta radiation - Photo-ionization detector (PID) -- uses UV light to produce ions
- Helium ionization detectorHelium ionization detectorA helium ionization detector is a type of detector used in gas chromatography.-Principle:An HID is an ion detector which uses a radioactive source to produce ions. The radioactive source ionizes helium atoms by bombarding them with emissions. As components elute from the GC's column they are...
(HID) -- uses a radioactive source to produce helium ions, which in turn ionize the components - Discharge ionization detectorDischarge ionization detectorA 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...
(DID) -- uses an electric sparkElectric sparkAn electric spark is a type of electrostatic discharge that occurs when an electric field creates an ionized electrically conductive channel in air producing a brief emission of light and sound. A spark is formed when the electric field strength exceeds the dielectric field strength of air...
source to produce helium ions, which in turn ionize the components - Pulsed discharge detector (PDD) -- similar to a Discharge ionization detectorDischarge ionization detectorA 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...
(DID), but uses a different sort of spark