Glossary of Gas Chromatography Terms
a gas mixture, produced either synthetically or by pumping natural air into
a high-pressure cylinder, that has been systematically analyzed to assign a
concentration value to a molecule or concentration values to several molecules
an inert gas that constantly flows through the
chromatography column and
detector. Carrier gas mobilizes the sample by pushing it
through the column. 'Inert' refers to non-reactivity of the carrier gas with the
sample and a low response of the detector to the carrier gas.
a class of fully chlorinated/fluorinated carbon-based molecules of the
general formula CnCljFk where j + k = 2n +2, k and j > 0. Uses have included
refrigeration, aerosol propellants, foam blowing, and cleaning solvents.
a length of metal or fused silica tubing filled or coated with one or more
packing material that separates the compounds of
interest as the sample mixture passes through.
a sensor that produces a measurable signal when certain molecules pass through
Electron-capture detector (ECD)
a detector that is especially sensitive to halogen-containing molecules. Thermal
electrons generated by the radioactive decay of 63Ni create a small, steady
current within the detector. This current is measurably reduced when certain
molecules capture electrons as they pass through the detector.
Gas chromatograph (GC)
a type of instrument based on the injection of component mixtures onto a
chromatography column, separation of the
components as the mixture passes through the column, and sensing of the
components of interest as they elute into a detector.
Gas sampling valve (GSV)
A multiple-port, two-position valve that changes the direction of gas flows
through chromatography columns and other
parts of an instrument. Used to fill a sample loop
with sample then inject the loop contents onto the column..
a class of carbon-based molecules having at least one halogen (fluorine,
chlorine, iodine) atom.
a class of brominated halocarbons of the general
formula CnBriCljFk where i + j + k = 2n + 2, i and k
> 0. Halons are typically
used as fire extinguishing agents.
a granular, solid-phase powder, sometimes also coated with a liquid phase, that
is used to fill a chromatography column.
The packing material of a column is chosen for its ability to separate the
molecules of interest from one another. Packing materials typically separate
molecules by their size (molecular sieves), boiling points, or polarities.
a length of hollow metal tubing whose fixed volume is filled with sample to a
repeatable pressure and its contents injected onto a chromatography column.
Consistent sample loop volume, pressure and temperature ensure that the same
amount of sample is injected for every analysis.
Stream selection valve (SSV)
A multiple-port, multiple-position valve that determines the source of gas
flowing through sample loops. Used to alternately analyze air samples and