Gas chromatography

1. Amandeep Singh
Assistant Professor
Department of Biotechnology
GSSDGS Khalsa College
Patiala

2. GAS CHROMATOGRAPHY
It is a type of Column chromatography. Stationary phase can be in solid or liquid form. If
stationary phase is in solid form then the technique will be called as Gas-Solid
Chromatography, If the stationary phase is in liquid phase, then the technique will be called as
Gas-Liquid Chromatography. Mobile phase will always be in gas phase.
Stationary Phase Mobile Phase
In GLC, Liquid phase dispersed on the solid surface of column and interacts with components
to be separated on the basis of their partition coefficient.
Solid Liquid Gas
Gas Solid
Chromatography
(GSC)
Gas Liquid
Chromatography
(GLC)
Carrier Gas
(named because it carries
sample components with itself)

3. Therefore, separation of components in GC is done on the basis of
their Distribution/Retardation Factor
Stationary/Liquid Phase (SP) Mobile/Gas Phase (MP)
Sample Retard More
distributed more in MP
Sample Retard Less
Sample (Volatile)
Distributed
between
distributed more in SP
Samples to be separated must be in volatile form and they get separated by their
distribution in the stationary or mobile phase. Samples distributed more in
stationary phase, remain in the column for longer period. Samples which distributed
more in mobile phase, travel along with mobile phase and spend less time in the
column. This simple principle cause their separation.

4. Chromatogram
Area under peaks tells us about
concentration of given component.
Separated Components
Elute from Column
Detector
Electrical Signal
in the form of peaks
Chromatogram
Retention Volume: Volume of gas traversed through column between the time that the sample
was applied and the time at which the particular component emerged out from the column.
Retention Volume
Sample In
Time
Sample Out
Time
Gas
Chromatogram is the graph that produced when separated samples elute from the column and
reach the detector. This graph is in the form of electrical signals in the form of peaks.

5. Carrier Gas (Mobile Phase)
Characteristics of carrier gas:
• Carrier gas must be Inert & Pure.
e.g. Nitrogen, Argon, Helium, Hydrogen, Carbon dioxide
Purity
• Gas must be free from contamination
Mostly contamination: Water vapours, which are removed by cold molecular sieve.
High Density Low Density
Pros: Better Separation
Cons: Long separation Time
Pros: Short separation Time
Cons: Poor Separation
Mobile phase can be of high density or low density which has it’s own pros and cons.
Mostly high density carrier gas is used as mobile phase for better separation.

6. Column
2 TYPES
Packed Column
Open Tubular/
Capillary Column
Wall Coated Open
Tubular Column
Support Coated Open
Tubular Column
Stainless steel, Copper, Glass tubing Provides Open unrestricted path for carrier gas in column

7. Solid Support
Properties:
1. Chemically Inert
2. Mechanically strong
3. Thermally stable
4. High surface area
Most Commonly used: Diatomaceous earth and Teflon
Deactivation of diatomaceous earth is required prior to use. Because surface of
diatomaceous earth is polar and it contains mineral impurities.
Sample components being polar, attach to diatomaceous earth surface which leads to long
retention time in column.
Mineral impurities acts as adsorption sites, where sample components adsorb which too
leads to long retention time in column.
Deactivation is done by 2 treatments:
1. Acid washing (remove mineral impurities)
2. Treatment with hexamethyl-disilazane (HMDS) make the surface inert, to polar
sample components.
Note: If sample is Non-polar/less polar: 1st treatment is enough.
If sample is Polar: Both treatments are required.

8. Liquid Phase (Stationary Phase)
Properties:
1. Chemically Inert
2. Thermally stable
3. Non-volatile
4. Good partition coefficient values for components to be separated
Liquid phase + low boiling solvent
(pentane, acetone)
Solvent evaporation
Packed column (In steps) Open Tubular column (In
steps)
Pouring the liquid phase by
straightening the column
Dilute liquid phase is forced
through column at a very slow
rate
Gently shaken & Tapping to
ensure even packing/ 5 psi
pressure is used
Excess solution is evaporated by
passing a hot carrier gas
Then, Both ends plugged with
glass wool
This results in thin layer of liquid
phase
Then, Column bend or coiled to
fit in oven.
Slow heating
Column FillingLiquid Phase Preparation

9. Sample Preparation and Introduction
Sample
Non-Polar/
Less Polar
Polar
No Pretreatment
Possess Polar functional Groups
-OH, -COOH, -NH2
Pretreatment is needed
If No Pretreatment, Sample retain in
Column for longer duration
Poor separation and Peak Tailing
Pretreatment by Derivatization:
1. Methylation
2. Silanization
3. Trifluoromethylsilanization
Increase volatility and distribution coefficient.

10. Introduction of Sample
After Pretreatment, Vaporization is done.
Sample must be introduced in vapour form. If sample is not already a vapour,
sample is heated to vaporize.
Liquid sample
Ether, Heptane, Methanol
Injected from a Syringe
into heated chamber
preceding the column
Dissolved in

11. Gas Solid Chromatography (GSC)
Stationary Phase (SP) Mobile Phase (MP)
Solid Gas
Not Inert
Therefore, Interact with sample components
Molecule/Component Separation
Adsorption-Desorption Property
Solid SP
Gas MP
Adsorption
Desorption
Sample Components
Out
Inert Column Surface
Inert Column Surface

12. GAS CHROMATOGRAPHY INSTRUMENT

13. DETECTORS
Temperature of Detector is maintained
1. Flame ionization detector
2. Electron capture detector
3. Thermionic emission detector
High Not Too High
To prevent condensation
of sample components
Cause decomposition of
sample components

14. 1. Flame ionization detector
Most widely used.
Hydrogen gas (carrier) used is burnt into a colorless flame.
2 electrodes = Polarizing electrode
Collector electrode
Flame change colour as the sample comes out of the column into the flame.
Sample components become ionized in the flame and give rise to current between the electrodes.

15. 2. Electron capture detector
This detector has the radioactive source, which ionize the carrier gas coming out
of the column
electrons
current
Sample component comes out of column
Capture electrons
Drop in current
Measured & Recorded

16. APPLICATIONS
1. Study of polymers, Lewis acid-base properties,
liquid crystals.
2. To study reaction rates and mechanism.
3. To study isotope labeled organic and inorganic
compounds
4. To study molecular properties such as vapor
pressure, heat of vaporization, molecular weight,
molecular geometry, bond angle deformation,
ionization potential and electron affinity.