HP 5890 Detector boards
There are many detectors which can be used in gas chromatography.
Different detectors will give different types of selectivity. A non-selective
detector responds to all compounds except the carrier gas, a selective
detector responds to a range of compounds with a common physical
or chemical property and a specific detector responds to a
single chemical compound. Detectors can also be grouped into concentration
dependant detectors and mass flow dependant detectors. The
signal from a concentration dependant detector is related to the
concentration of solute in the detector, and does not usually destroy
the sample Dilution of with make-up gas will lower the detectors
response. Mass flow dependant detectors usually destroy the sample,
and the signal is related to the rate at which solute molecules enter
the detector. The response of a mass flow dependant detector is
unaffected by make-up gas.
A number of detectors are used in gas chromatography. The most common are the flame ionization detector (FID) and the thermal conductivity detector (TCD). Both are sensitive to a wide range of components, and both work over a wide range of concentrations. While TCDs are essentially universal and can be used to detect any component other than the carrier gas (as long as their thermal conductivities are different than that of the carrier gas, at detector temperature), FIDs are sensitive primarily to hydrocarbons, and are more sensitive to them than TCD. Both detectors are also quite robust. Since TCD is non-destructive, it can be operated in-series before an FID (destructive), thus providing complementary detection of the same
Some gas chromatographs are connected to a mass spectrometer which acts as the detector. The combination is known as GC-MS.
|Flame ionization (FID)
||Hydrogen and air
||Most organic cpds.
|Thermal conductivity (TCD)
|Electron capture (ECD)
||Halides, nitrates, nitriles, peroxides, anhydrides,
||Hydrogen and air
|Flame photometric (FPD)
||Hydrogen and air possibly oxygen
||Sulphur, phosphorus, tin, boron, arsenic, germanium, selenium,
||Aliphatics, aromatics, ketones, esters, aldehydes, amines,
heterocyclics, organosulphurs, some organometallics
|Hall electrolytic conductivity
||Halide, nitrogen, nitrosamine, sulphur