Analytical separation technique where the minor components in a mixture of gases are separated and resolved into individual components. The technique requires the transmission of the gas sample through a column in the chromatograph using a mobile phase or carrier gas. The column is either packed or coated with a material for which the gases to be separated have an affinity and the strength of this affinity largely determines the time any individual component is retained in the column. Various detectors are employed in gas chromatography, from very specific compound-responsive detectors (flame photometric detector, electron capture detector, photoionization detector, etc. ) to some very generally sensitive detectors (flame ionization detector, thermal conductivity detector, atomic emission detector, etc. ) Gas chromatography is commonly used for the quantification of halocarbons and hydrocarbons in the atmosphere.