Gas chromatography is a technique that separates volatile organic compounds using a carrier gas and a column with a stationary phase. The basic system includes an injection port, separation column in an oven, and detector. Samples are vaporized and carried by the gas through the column where compounds separate based on interactions with the stationary phase and exit the column at different rates, known as elution. The detector measures the compounds and generates a chromatogram to identify and quantify the separated components. Common detectors include the flame ionization detector. Gas chromatography has various applications like analysis of biological samples.

1. GAS CHROMATOGRAPHY
ALI HAMZA
Master of Science in Zoology
UOG

2. 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)
an oven
a detector.

3. 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
oven.
 The solutes travel through the column at a rate primarily
determined by their physical properties, and the temperature and
composition of the column.

4.  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
order.
 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 used
to produce a chromatogram.

5. TYPES OF GC
Two types of gas chromatography
1. Gas-solid chromatography (GSC)
2. Gas-liquid chromatography(GLC)
Gas-solid chromatography
Is based upon a solid stationary phase
on which retention of analytes is the
consequence of physical adsorption.
Gas-liquid chromatography
Is useful for separating ions or
molecules that are dissolved in a solvent.

6. INSTRUMENTAL COMPONENTS
CARRIER GAS
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.

7. COLUMNS
There are two types of column,
1.Packed column
2. capillary column (also known as open tubular).
PACKED COLUMNS
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 -
4mm.
CAPILLARY COLUMNS
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
reactivity.

8. DETECTORS
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
5.Photo-ionization detector
6.Hall electrolytic conductivity detector

9. 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
is measured.
 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.

10. 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
by GC
 Non-volatile substance can also separated if converted
in to volatile one by oxidation, acylation, alkylation,
etc.
 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.

11. REFERENCES
 Biomedical instrumentation- V.Arumugam
 Palanivelu. P. Analytical biochemistry and separation
techniques.
 Webster. J.G. Bioinstrumentation.
 Bioinstrumentation- L.Veerakumari.
www.detectors of gas chromatography.com.au
www.science info world of gas chromatography.
www.gas cromatography.edu.au