Gas chromatography- Basics

1. By
Akhil Benny
Assistant Professor
Department of Forensic Science
KJC- Bengaluru
Course Code MFS204A24
Course Title Instrumentation
Unit I
Topic Gas Chromatography

2. Gas
Chromatography

3. Introduction
• Gas chromatography (GC) is probably the most utilized chromatographic
technique.
• Since the 1950s, GC has been used for the separation of amino acids, and
now it has applications in analyzing drugs, foodstuff, petrochemicals,
pesticides, and more.
• GC is similar to column chromatography, but it uses gas as the mobile phase
instead of a liquid.

4. Types of Gas Chromatography
• 1. Gas-Liquid Chromatography (GLC): Uses a non-volatile liquid as the
stationary phase.
• - Separation occurs by partition.
• 2. Gas-Solid Chromatography (GSC): Uses a solid adsorbent as the stationary
phase.
• - Separation occurs by adsorption.
• GLC is more popular due to its broader applications.

5. Advantages of
Gas
Chromatography
1. High resolving
power, even for
complex
mixtures.
2. High sensitivity,
requiring only a
few milligrams of
sample.
3. Good precision
and accuracy.
4. Short analysis
time.
5. Cost-effective
and long-lasting
equipment.
6. Easy operation,
suitable for
routine analysis.

6. Principle of Gas
Chromatography
The principle is based on the partitioning
of a gas or vapor between the mobile
phase (carrier gas) and stationary phase
(solid or liquid).
1. Adsorption follows Freundlich or
Langmuir laws.
2. Partitioning follows Henry’s law.
3. Components are separated based on
their distribution coefficients.

7. Gas-Liquid
Chromatography
(GLC)
1. Mobile phase: Gas.
2. Stationary phase: Liquid
coated on a solid matrix or
capillary tube wall.
3. Separation is achieved by
differences in retention times of
components.
4. Detection is performed at the
column exit.

8. Instrumentation
of Gas
Chromatography
1. Carrier gas: Inert gas with high
reproducibility.
2. Sample injection system.
3. Separation column (glass, metal,
or Teflon).
4. Detectors (e.g., FID, TCD).
5. Thermostat chambers for
temperature control.
6. Amplification and recording
system.

9. Column in Gas
Chromatography
1. Stationary phase: Adsorbent
or liquid-coated support.
2. Mobile phase: Carrier gas for
sample transport.
3. Sorption-desorption process
leads to separation.
4. Gaussian distribution is
observed for component bands.

10. Detector
and Role
1. The detector is the 'brain' of the
chromatograph.
2. It measures the eluted
components based on specific
properties (e.g., ionization, thermal
conductivity).
3. The column acts as the 'heart,'
enabling separation.