Gas chromatography is a technique used to separate gaseous and volatile substances. It works by carrying a sample mixture through a column via an inert carrier gas. Components interact differently with the stationary phase in the column, causing separation. The separated components then enter a detector which converts detection into electrical signals and peaks on a chromatogram. Common applications include forensic analysis, quality control, and environmental monitoring.

1. Gas Chromatography
 Prepared by: Sathe Komal
Pramod
 College: HSBPVT’s GOI
College of Pharmacy Kashti
 Roll No: 117

2. Gas chromatography is a widely used
technique for separation of gaseous & volatile
substances.
 Mobile phase- Inert carrier Gas (Helium,
Nitrogen)
 Stationary phase- Solid or liquid
Solid: Silica or Alumina
Liquid: Polyethylene glycol
 Gas- solid chromatography (GSC): Stationary phase is
solid
 Gas- liquid chromatography (GLC): Stationary phase
is liquid

3. GC system

4. Instrumentation
1. Carrier Gas supply
• Main purpose- to transport sample components
through the columns.
• Gas must be inert, should not interact with sample,
highly pure, safe.
• Associated with the gas supply are pressure
regulators, flow meters, pressure gauze. In addition,
carrier gas system contains molecular sieve, filter,
drier to remove moisture & impurities.

5. 2. Sample injection system
The sample is introduced in the column in the form of a
sharp plug through an injection port.
The injection port contains a gas tight rubber septum
through which the sample is injected by means of syringe

6. Immediately after injection, the sample has to be vaporized
and flown into the column with minimum pressure change,
flow rate and back diffusion.
For this purpose injection ports are heated.
The temperature of sample injection port is kept 20-25
degree C above the column temperature.
a)Gas sample- introduced by hexport gas sampling valve.
b)Liquid sample- introduced by means of microsyringe.
c)Solid sample- samples weighed into thin glass
ampoules, sealed & placed in the gas stream & then
crushed in the ancillary tube which is heated by heating
coils to vaporize the sample.

7. 3. Column Technology
Heart of the GC system where the separation takes remarkably.
a)The column- Depending upon the separation, columns
may vary in shape.
2 types of column shapes: Coiled helix & U tube type.
Made up of glass, aluminium, copper, steel cupronickel or
stainless steel.
W- type columns are used for separation of compounds
from biological products.

8. b) Support medium- Purpose of solid support is to
provide large & inert surface area for holding liquid phase in
thin & uniform film.
• It must be poor adsorbent, chemically inert, heat stable,
mechanically strong.
• Most common supports are available from Diatomaceous
earth. 2 types are available: Firebrick & Kieselguhr.
• Glass beads, porous polymers, unglazed tiles, sand,
fluorinated resins are also used as support system.
c) Liquid phase- requirements for selecting a liquid phase
are Non volatility, compatibility, selectivity, low viscosity,
chemically inert.

9. 3 types of chromatographic columns are used in GC
1. Packed columns
Prepared by packing metal or glass
tubing with granular stationary
phase.
 For GSC- columns are packed with
adsorbents or porous polymers.
 For GLC- columns are packed by
coating the liquid phase over an
inert solid support.
2. Open tubular columns/
Capillary columns/ Golay
columns
Prepared from long capillary tubing
having uniform & narrow internal
diameter. Sample capacity is low.

10. 3. Support Coated Open Tubular columns (SCOT)
 made by depositing a micron size porous layer of support
material inside wall of capillary column & then coating
with a thin film or liquid phase.
 Sample capacity is higher.
 The mixtures are separated by their relative adsorption /
solubility to the stationary phase.
 The time taken for a component to leave the column is
called the retention time.

11. 4. Detectors
 Vaporized component emerges in turn from column & is
carried into the detector mixed with carrier gas.
 Vapor is sensed by the detector. It converts this impulse
into an electrical signal.
 This signal is amplified & recorded as a peak on the
chromatograph.

12. Types of detectors
 Thermal conductivity detectors
 Flame ionization detector
 Electron capture detector
 β- ray ionization detector
 Applications of GC
 Forensic science
 Blood alcohol analysis
 Food analysis
 Quality control of chemicals & pharmaceuticals
 Analysis of new products
 Monitoring metabolites in biological fluids
 Measuring air pollution