GAS CHROMATOGRAPHY (GC)
*Gas chromatography is a chromatographic technique that can be used
to separate volatile organic compounds.
*GLC( or) GC is a type of partition chromatography.
*It consists of
a flowing mobile phase (carrier gas)
an injection port
a separation column (the stationary phase)
BASIC GC SYSTEM
One or more high purity gases are supplied to the GC. One of the
gases (called the carrier gas) flows into the injector, through the
column and then into the detector.
A sample is introduced into the injector usually with a syringe or
an exterior sampling device. The injector is usually heated to
150-250°C which causes the volatile sample solutes to vaporize.
The vaporized solutes are transported into the column by the
carrier gas. The column is maintained in a temperature controlled
The solutes travel through the column at a rate primarily
determined by their physical properties, and the temperature and
composition of the column.
The various solutes travel through the column at different
rates. The fastest moving solute exits (elutes) the column first
then is followed by the remaining solutes in corresponding
As each solute elutes from the column, it enters the heated
detector. An electronic signal is generated upon interaction of
the solute with the detector.
The size of the signal is recorded by a data system and is
plotted against elapsed time to produce a chromatogram.
TYPES OF GC
Two types of gas chromatography
1. Gas-solid chromatography (GSC)
2. Gas-liquid chromatography(GLC)
Is based upon a solid stationary phase
on which retention of analytes is the
consequence of physical adsorption.
Is useful for separating ions or
molecules that are dissolved in a solvent.
PRINCIPLE OF GC
The GC principle involves separation of components of the sample under
test due to partition in between gaseous mobile phase and stationary
Gas chromatography runs on the principle of partition
chromatography for separation of components. In terms of stationary
and mobile phases it is categorized under gas-liquid type
of chromatography .
The organic compounds are separated due to differences in their
partitioning behavior between the mobile gas phase and the stationary
phase in the column.
Process Flow Schematic
Long Column (30 m)
detector or FID)
Gas Chromatograph Components
The carrier gas must be chemically
inert. Commonly used gases include
nitrogen, helium, argon, and carbon dioxide.
SAMPLE INJECTION PORT
The most common injection method is
where a micro syringe is used to inject
sample through a rubber septum into a flash
vaporizer port at the head of the column. The
temperature of the sample port is usually
about 50°C higher than the boiling point of
the least volatile component of the sample.
The carrier gas enters the chamber and can
leave by three routes. The sample vaporizes
to form a mixture of carrier gas, vaporized
solvent and vaporized solutes.
There are two types of column,
2. capillary column (also known as open tubular).
It contain a finely divided, inert, solid support material coated with liquid stationary
phase. Most packed columns are 1.5 - 10m in length and have an internal diameter of 2 -
1. wall-coated open tubular (WCOT)
2. support-coated open tubular (SCOT)
Both types of capillary column are more efficient than packed columns.
These have much thinner walls than the glass capillary columns, and are given strength by
the polyimide coating. They have the advantages of physical strength, flexibility and low
PREPARATION OF SAMPLE
Polar compounds are not directly applied. polar groups (-OH, -
COOH) into non-polar derivatives increases the volatility of these
compounds. Silanization, methylation and perfluoroacylation are common
conversion methods for CHO, fatty acids & amino acids. Non-polar organic
compounds need any such conversion and they can be directly applied.
APPLICATION OF SAMPLE
The sample for GLC is dissolved in a suitable solvent such as
acetone or methanol and is injected into the column using a micro syringe in
the injecting port.
The most commonly used carrier gases are nitrogen, helium
& argon. The gases are passed at a flow rate of 40 to 80 ml.
Two types of temperature control techniques:
1. Isothermal analysis
2. Temperature programming
GC detectors detect the isolated components and helps in
identification and quantification of the sample.
TYPES OF GC DETECTORS
1.Thermal conductivity detector
2.Flame ionization detector
3.Electron capture detector
4.Flame photometric detector
6.Hall electrolytic conductivity detector
FLAME IONIZATION DETECTOR
The effluent from the column is mixed with hydrogen and air.
Organic compounds burning in the flame produce ions and
electrons which can conduct electricity through the flame.
A large electrical potential is applied at the burner tip, and a
collector electrode is located above the flame.
The current resulting from the pyrolysis of any organic compounds
The FID is a useful general detector for the analysis of organic
compounds, it has high sensitivity, a large linear response range,
and low noise.
It is also easy to use, but unfortunately, it destroys the sample.
Flame Ionization Detector
Teflon insulating ring
Capillary tube (column)
Coaxial cable to
Analog to Digital
ELECTRON CAPTURE DETECTOR
The computer to record the analysed readings. This is
connected with the detector and hence records the detector
changes in reference to the flow of separated components from
the exit of the column. The record is called gas chromatograph.
The thermal chamber to fix or maintain fixed temperature.
Further improvement in GC apparatus is fixed with Mass
spectroscopy system (GC-MS) for better analysis of
GAS CHROMATOGRAPH OUTPUT
•Peak area proportional to mass of
•Peak time dependent on velocity through
USES OF GC
Widely used for the qualitative and quantitative
analysis of a large number of compounds
This technique provides a high speed and resolution
Very good reproducibility and high sensitivity
1000 of volatile organic compounds can be separated
Non-volatile substance can also separated if converted
in to volatile one by oxidation, acylation, alkylation,
Concentration of individual elements such as carbon
and hydrogen can be determined very accurately
Alcohols, esters, fatty acids and amines present in
biological samples are often separated by GC.
APPLICATION OF GC
Gas chromatography (GC) continues to play an important role in
the identification and quantification of ubiquitous pollutants in
GC in the analysis of various classes of persistent organic
contaminants in air, water, soils, sediments. Special attention is
given to sample-preparation techniques.
The organic pollutant groups are: volatile organic compounds
(VOCs) , polycyclic aromatic hydrocarbons (PAHs) , pesticides
and halogenated compounds.
Trends and future perspectives of capillary GC in the field of
1) REFINERY SOLUTIONS
Gas Chromatographs are uniquely designed to
provide extended analysis in the most extreme of
plant condition. Emerson gas chromatograph
• Better control of the process
• Environmental monitoring
• Billing and cost accounting for product
2) CHEMICAL/PETROCHEMICAL SOLUTIONS
chemical and petrochemical plants keep operating efficiently.
• Maintain proper chemical ratios
• Monitor for unconverted carbons
• Monitor purge gas rates and track BTU usage
& variations in product feed composition
• Measure impurities in product
• Minimize product loss
3) GAS PROCESSING SOLUTIONS
For gas processing plants, gas chromatograph product
and service offerings reduce installation and maintenance
costs, while improving process quality.
We offer a complete range of gas plant applications
that demonstrate an advanced combination of innovative
technology and hardened instrumentation
Gas Processing Solutions
4) ENVIRONMENTAL MONITORING
There are numerous gases found in industrial process
plants that are harmful should a gas leak occur, such as
sulfur dioxide, hydrogen sulfide, and others.
Analytical process gas chromatographs provides
reliable, accurate analysis of gases. A Analytical process
gas chromatograph offers a sensitivity of 100%
humidity, and even samples will not deter accurate
Biomedical instrumentation- V.Arumugam
Palanivelu. P. Analytical biochemistry and separation
Webster. J.G. Bioinstrumentation.
www.detectors of gas chromatography.com.au
www.science info world of gas chromatography.
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