between them, and collisions between molecules would be perfectly
elastic. In practice, however, the behaviour of real gases deviates from
the gas laws because their molecules
occupy a Ünite volume, there are
small forces between molecules, and
in polyatomic gases collisions are to a
certain extent inelastic (see equation
of state).
gas chromatography A technique
for separating or analysing mixtures
of gases by *chromatography. The
apparatus consists of a very long tube
containing the stationary phase. This
may be a solid, such as kieselguhr
(gas–solid chromatography, or GSC),
or a nonvolatile liquid, such as a hydrocarbon oil coated on a solid support (gas–liquid chromatography, or
GLC). The sample is often a volatile
liquid mixture, which is vaporized
and swept through the column by a
carrier gas (e.g. hydrogen). The components of the mixture pass through
the column at different rates because
they adsorb to different extents on
the stationary phase. They are detected as they leave, either by measuring the thermal conductivity of the
gas or by a Ûame detector.
Gas chromatography is usually
used for analysis; components can be
identiÜed by the time they take to
pass through the column. It is sometimes also used for separating mixtures.
Gas chromatography is often used
to separate a mixture into its components, which are then directly injected into a mass spectrometer. This
technique is known as gas chromatography–mass spectroscopy or
GCMS.
gas chromatography infrared
(GC-IR) A form of *Fourier-transform
infrared (FT-IR) used to identify small
amounts of gas obtained by gas chromatography. Since functional groups
in molecules are characteristic in infrared spectra this produces information to supplement that obtained by
mass spectrometry. It is easier to perform FT-IR for gas chromatography
than for liquid chromatography because carrier solvents in liquid
chromatography absorb infrared
radiation.
gas constant (universal molar gas
constant) Symbol R. The constant
that appears in the universal gas
equation (see gas laws). It has the
value 8.314 510(70) J K
–1 mol
–1 .
gas equation See gas laws.
gasiÜcation The conversion of
solid or liquid hydrocarbons to fuel
gas. Solid fuels such as coal or coke
are converted into producer gas (carbon monoxide) or water gas (carbon
monoxide and hydrogen) by the action of air (or oxygen) and steam.
Solid fuels may also be hydrogenated
to produce methane. Liquid fuels,
from petroleum, are gasiÜed to produce synthesis gas (carbon monoxide
and hydrogen) or town gas (mostly
hydrogen and methane), usually by
*cracking or *hydrogenation.
gas laws Laws relating the temperature, pressure, and volume of an
*ideal gas. *Boyle’s law states that
the pressure (p) of a specimen is inversely proportional to the volume
(V) at constant temperature (pV = constant). The modern equivalent of
*Charles’ law states that the volume
is directly proportional to the thermodynamic temperature (T) at constant pressure (V/T = constant);
originally this law stated the constant expansivity of a gas kept at constant pressure. The pressure law
states that the pressure is directly
proportional to the thermodynamic
temperature for a specimen kept at
constant volume. The three laws can
be combined in the universal gas
gas chromatography
242
g
www.AzShimi.ir www.AzShimi.com
elastic. In practice, however, the behaviour of real gases deviates from
the gas laws because their molecules
occupy a Ünite volume, there are
small forces between molecules, and
in polyatomic gases collisions are to a
certain extent inelastic (see equation
of state).
gas chromatography A technique
for separating or analysing mixtures
of gases by *chromatography. The
apparatus consists of a very long tube
containing the stationary phase. This
may be a solid, such as kieselguhr
(gas–solid chromatography, or GSC),
or a nonvolatile liquid, such as a hydrocarbon oil coated on a solid support (gas–liquid chromatography, or
GLC). The sample is often a volatile
liquid mixture, which is vaporized
and swept through the column by a
carrier gas (e.g. hydrogen). The components of the mixture pass through
the column at different rates because
they adsorb to different extents on
the stationary phase. They are detected as they leave, either by measuring the thermal conductivity of the
gas or by a Ûame detector.
Gas chromatography is usually
used for analysis; components can be
identiÜed by the time they take to
pass through the column. It is sometimes also used for separating mixtures.
Gas chromatography is often used
to separate a mixture into its components, which are then directly injected into a mass spectrometer. This
technique is known as gas chromatography–mass spectroscopy or
GCMS.
gas chromatography infrared
(GC-IR) A form of *Fourier-transform
infrared (FT-IR) used to identify small
amounts of gas obtained by gas chromatography. Since functional groups
in molecules are characteristic in infrared spectra this produces information to supplement that obtained by
mass spectrometry. It is easier to perform FT-IR for gas chromatography
than for liquid chromatography because carrier solvents in liquid
chromatography absorb infrared
radiation.
gas constant (universal molar gas
constant) Symbol R. The constant
that appears in the universal gas
equation (see gas laws). It has the
value 8.314 510(70) J K
–1 mol
–1 .
gas equation See gas laws.
gasiÜcation The conversion of
solid or liquid hydrocarbons to fuel
gas. Solid fuels such as coal or coke
are converted into producer gas (carbon monoxide) or water gas (carbon
monoxide and hydrogen) by the action of air (or oxygen) and steam.
Solid fuels may also be hydrogenated
to produce methane. Liquid fuels,
from petroleum, are gasiÜed to produce synthesis gas (carbon monoxide
and hydrogen) or town gas (mostly
hydrogen and methane), usually by
*cracking or *hydrogenation.
gas laws Laws relating the temperature, pressure, and volume of an
*ideal gas. *Boyle’s law states that
the pressure (p) of a specimen is inversely proportional to the volume
(V) at constant temperature (pV = constant). The modern equivalent of
*Charles’ law states that the volume
is directly proportional to the thermodynamic temperature (T) at constant pressure (V/T = constant);
originally this law stated the constant expansivity of a gas kept at constant pressure. The pressure law
states that the pressure is directly
proportional to the thermodynamic
temperature for a specimen kept at
constant volume. The three laws can
be combined in the universal gas
gas chromatography
242
g
www.AzShimi.ir www.AzShimi.com