Gas chromatograph (GC): An
instrument for separating substances via
column
chromatography, where the mobile phase is a gas (called the
carrier gas; usually helium). The study of a sample using a gas
chromatograph is called
gas chromatography.
'Gas chromatograph' may also refer to the output from the
instrument.
The gas chromatograph has an electronic device that detects and
quantifies the separated substances as they leave the instrument's
column. The device is the detector. Some commonly used detectors
are a
mass
spectrometer (in the case the instrument is a
gas
chromatograph-mass spectrometer or GC-MS, a
thermal
conductivity detector (
TCD; measures changes in the
exiting gas stream), and
flame ionization
detector (
FID; detects substances in the exiting gas
stream by
burning
and measuring the
ions
produced).
