Gas chromatography is a technique used to separate components in a mixture based on how they partition between a mobile gas phase and a stationary liquid or solid phase. Key aspects of gas chromatography include a carrier gas that moves the sample mixture through a column coated with a liquid or solid stationary phase, causing different components to elute out of the column at different retention times based on their interaction with the stationary phase. Common applications of gas chromatography include analysis of drugs, food, body fluids, and other mixtures to separate and identify volatile organic compounds.

1. GAS CHROMATOGRAPHY

2. Contents:-
Introduction
Principle
Instrumentation
Working
Advantages
Disadvantages
Uses

3. Introduction:-
Gas chromatography:- It is a process of separating components from
the given crude drug by using a gaseous mobile phase
The father of modern gas chromatography is noble prize winner John Porter Martin,
who also developed the first liquid-gas chromatography.
It involves separation of gaseous and volatile phase at a high temperature.
It is simple & efficient In regard to separation.
Gas chromatography has two major types:-
Gas-solid chromatography:- Here, the mobile phase is gas while stationary
phase is solid.eg.,H2, S, CS2, CO etc.
Gas-liquid chromatography:-The mobile phase is a gas while the stationary
phase is a liquid.

4. Principle:-
The principle of gas chromatography is “partition chromatography”.
The mixture of components to be separated is converted to vapours and mixed with
gaseous mobile phase.
The component which is more soluble in stationary phase travel slowly and eluted
later. The component which is not soluble in stationary phase travels faster and eluted
out first.
The organic comp. are separated due to the difference in their partitioning behavior
between the mobile phase and the stationary phase in the column.

5. Instrumentation:-
1.Carrier Gas :-
Hydrogen:-Good thermal conductivity, Low density, Inflammable.
Helium:-Good thermal conductivity, But Expensive.
2.Flow Regulators or Flow meters:-
Rotameter:-Placed before the column inlet.
Soap bubble meter.
3. Injection Devices:-
Direct injection is mostly used.
Types:- 1.Automatic sampler
2.Headspace Sampling

6. Cont..
4.Column Unit:
Support Phase:-
It`s main function is to provide mechanical support to the liquid phase.
an ideal support should have a large surface area, chemically inert, should be
thermostable. Eg, diatomaceous earth, glass beads.
Liquid Phase:-
should be non-volatile.
chemically inert.
Types:-
(a) capillary column(15-60 m in length and have internal diameter of
0.1- 0.53mm)
(b) packed column(1.5-10 m in length and have internal
diameter of 2-4 mm)

7. Two operations are available:-
1.Isothermal Programming:-same temp .throughout process.
2.Linear Programming:-oven heated linearly to the period of time.
6.Detectors
1.Thermal conductivity detector:-based on the electronic circuit known as
wheat-stone bridge.(detection limit is 10ppm)
2.Flame ionization detectors:- universal detector capable of measuring the
presence of almost any organic and many inorganic compounds.(detection
limit is 0.1ppm ,cannot detect formaldehyde and formic acid)
3.Thermionic detectors:-used for detecting nitrogen or phosphorus
containing compounds .(1ppb)
4.Electron capture detector:- radiation based detector.
-selective for comp. containing
electronegative atoms, such as halogens.
(0.1ppb)
5.Temperature Control Devices

8. Working of Gas Chromatography:-
The sample is first introduced into the gas chromatograph(GC), either
with a syringe or transferred from an autosampler that may also
extract the chemical components from solid or liquid sample .The
sample is injected into GC inlet through septum which enables the
injection of the sample mixture without losing the mobile phase. For
liquid sample in both the packed and capillary GC the typical sample
volume ranges from (0.1-10uL).For gas sample, volume ranges from a
few uL to 1mL or more.
Connected to the inlet is the analytical column, a long (10-150m),
narrow(0.1-0.53 in diameter)fused silica or metal tube which contains
the stationary phase coated on the inside walls.
The analytical column is held into the column oven which is heated
during the analysis to elute the less volatile components.
The outlet of the column is inserted into the detector which
responds to the chem. Components eluting from the column to
produce a signal.
The signal is recorded by the acquisition software on a computer to
produce a chromatograph.

9. Advanatges:-
High Sensitivity.
High Accuracy and Precision.
Analysis of sample can be done very quickly.
Universal detector for organic compounds.
Mobile phase impurities are not detected.
Disadvantages:-
Limited to volatile sample.
Not suitable for thermolabile components.

10. Applications of GC:-
Dairy product analysis-rancidity.
Separation and identification of Volatile Materials.
Analysis of body fluids like blood, lymph etc..
Used for the analysis of drugs and their metabolites.
can be used to detect the moisture content
in various crude drugs like sandalwood etc.