Flame Ionization Detector
Definition and meaning of Flame Ionization Detector in chemistry.
A flame ionization detector (FID) is a gas chromatography detector that identifies and quantifies organic compounds by burning them in a hydrogen-air flame and measuring the resulting electrical current.
In more detail
As carbon-containing analyte molecules elute from the GC column into the flame, they are pyrolyzed and ionized, chiefly through the reaction of CH radicals with oxygen to form CHO+ ions and electrons. A polarized collector electrode above the flame captures these charged species, producing a current roughly proportional to the number of reduced carbon atoms burned per second. FIDs are valued for their wide linear range, high sensitivity (down to picogram quantities), and durability, but they give little or no response to compounds lacking C-H bonds, such as water, carbon dioxide, and the noble gases.
Key facts
| Field | Analytical Chemistry |
|---|---|
| Detects | Carbon-containing (organic) compounds |
| Flame gases | Hydrogen and air (or oxygen) |
| Common use | Gas chromatography (GC-FID) |
In GC-FID analysis of a gasoline sample, each separated hydrocarbon component produces a peak whose area is approximately proportional to the mass of carbon it contains, allowing quantification of components like benzene and octane.
Frequently asked questions
Why doesn't an FID detect water or carbon dioxide?
FID response depends on forming CH radicals from C-H bonds in the flame; since H2O and CO2 contain no C-H bonds, they generate essentially no ions and produce little to no signal.
What gases does an FID require?
It needs hydrogen and air (or oxygen) to sustain the flame, along with an inert carrier gas, typically helium or nitrogen, to carry the sample from the column.