98 Gas chromatography
Ingas chromatography(GC) the analyte and mobile phase must both be gases or be
readily introduced into the gas phase by heating. The mobile phase gas must be inert
and not reacting with the sample to be analysed. Examples of inert gases are helium and
nitrogen gas.
The gases are passed through a long, narrow (and most often, coiled) tube either packed
with a porous stationary phase or whose inner walls are coated with a stationary phase,
and the analyte components are detected as they emerge from the far end of the tube. The
tube is commonly known as GC column.
Often a time-varying temperature gradient, from lower temperature to higher temperature,
is applied to the tube. This first allows the analyte components to partition into the
stationary phase and then, as the temperature rises, to differentially force them back into
the mobile phase.
Common detectors for gas chromatography are flame ionization detector (FID), electron
capture detector (ECD) and mass spectrometry (MS). Different types of sample analysis
would require the use of a different type of detectors.