Gas chromatography (GC) is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. Typical uses of GC include testing the purity of a particular substance, or separating the different components of a mixture (the relative amounts of such components can also be determined). In some situations, GC may help in identifying a compound. In preparative chromatography, GC can be used to prepare pure compounds from a mixture

1. GAS CHROMATOGRAPHY
Prepared By -
D.Mahendra,M.Pharm,(Ph.D),.
Dept of Ph.Analysis & Quality Assurance
Research Scholar at PARUL University,
Asst.Professor at NCOP_JNTUK
Email – Mahendra888d@gmail.com
Mobile- 9912360343

2. Gas Chromatography

3. What is Gas Chromatography?
• It is also known as…
– Gas-Liquid Chromatography (GLC)

4. GAS CHROMATOGRAPHY
 Separation of gaseous & volatile substances
 Simple & efficient in regard to separation
GC consists of GSC (gas solid chromatography)
GLC (gas liquid chromatography
Gas → M.P
Solid / Liquid → S.P
GSC not used because of limited no. of S.P
GSC principle is ADSORPTION
GLC principle is PARTITION

5. Sample to be separated is converted into vapour
And mixed with gaseous M.P
Component more soluble in the S.P → travels slower
Component less soluble in the S.P → travels faster
Components are separated according to their
Partition Co-efficient
Criteria for compounds to be analyzed by G.C
1.VOLATILITY:
2.THERMOSTABILITY:

6. What is Gas Chromatography?
• The father of
modern gas
chromatography is
Nobel Prize winner
John Porter Martin,
who also developed
the first liquid-gas
chromatograph.
(1950)

7. The Next Generation in Gas
Chromatography

8. How a Gas Chromatography Machine
Works
– First, a vaporized sample is injected onto the
chromatographic column.
– Second, the sample moves through the
column through the flow of inert gas.
– Third, the components are recorded as a
sequence of peaks as they leave the column.

13. PRACTICAL REQUIREMENTS
• Carrier gas
• Flow regulators & Flow meters
• Injection devices
• Columns
• Temperature control devices
• Detectors
• Recorders & Integrators

14. CARRIER GAS
» Hydrogen
better thermal conductivity
disadvantage: it reacts with unsaturated
compounds & inflammable
» Helium
excellent thermal conductivity
it is expensive
» Nitrogen
reduced sensitivity
it is inexpensive

15. Requirements of a carrier gas
 Inertness
 Suitable for the detector
 High purity
 Easily available
 Cheap
 Should not cause the risk of fire
 Should give best column performance

16. Flow regulators & Flow meters
 deliver the gas with uniform pressure/flow
rate
 flow meters:- Rota meter & Soap bubble
flow meter
Rota meter
placed before column inlet
it has a glass tube with a float held on to a
spring.
the level of the float is determined by the
flow rate of carrier gas

18. Soap Bubble Meter
◊ Similar to Rota meter & instead of a float,
soap bubble formed indicates the flow rate

19. Injection Devices
 Gases can be introduced into the column by
valve devices
 liquids can be injected through loop or
septum devices

20. COLUMNS
• Important part of GC
• Made up of glass or stainless steel
• Glass column- inert , highly fragile
COLUMNS can be classified
Depending on its use
1. Analytical column
1-1.5 meters length & 3-6 mm d.m
2. Preparative column
3-6 meters length, 6-9mm d.m

21. Columns
• Packed
• Capillary

22. Equilibration of the column
 Before introduction of the sample
 Column is attached to instrument &
desired flow rate by flow regulators
 Set desired temp.
Conditioning is achieved by passing
carrier gas for 24 hours

23. DETECTORS
Heart of the apparatus
The requirements of an ideal detector are-
 Applicability to wide range of samples
 Rapidity
 High sensitivity
 Linearity
 Response should be unaffected by
temperature, flow rate…
 Non destructive
 Simple & inexpensive

24. TYPES OF DETECTORS
1. FLAME IONISATION DETECTOR – FID
2.THERMAL CONDUCTIVITY DETECTOR- TCD
3.ORGAN IONISATION DETECTOR
4.ELECTRON CAPCTURE DETECTOR- ECD

25. Measures the changes of thermal conductivity due
to the sample (g). Sample can be recovered.
1.Thermal Conductivity Detector
(Katharometer, Hot Wire Detector)

26. When a separated compound elutes from the
column , the thermal conductivity of the
mixture of carrier gas and compound gas is
lowered. The filament in the sample column
becomes hotter than the control column.
The imbalance between control and sample
filament temperature is measured by a simple
gadget and a signal is recorded
Thermal Conductivity Detector

28. Flame Ionization Detector
 Destructive detector
 The effluent from the column is mixed with H
& air, and ignited.
 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
 The ions collected on collector or electrode
and were recorded on recorder due to
electric current.

29. FID

30. Argon ionization detector
 Depends on the excitation of argon atoms to a
metastable state, by using radioactive energy.
Argon→ irradiation Argon + e- →collision Metastable
Argon→ collision of sub. → Ionization →↑Current
ADVANTAGES
1.Responds to organic compounds
2.High sensitivity
DISADVANTAGES
1.Response is not absolute
2.Linearity is poor
3. Sensitivity is affected by water

31. ELECTRON CAPTURE DETECTOR
The detector consists of a cavity that
contains two electrodes and a radiation
source that emits  - radiation (e.g.63Ni,
3H)
The collision between electrons and the
carrier gas (methane plus an inert gas)
produces a plasma containing electrons
and positive ions.

33. RECORDERS & INTEGRATORS
Record the baseline and all the peaks obtained
INTEGRATORS
Record the individual peaks with Rt, height….

34. Parameters used in GC
Retention time (Rt)
It is the difference in time b/w the point of
injection & appearance of peak maxima. Rt
measured in minutes or seconds
(or) It is the time required for 50% of a
component to be eluted from a column
Retention volume (Vr)
It is the volume of carrier gas which is
required to elute 50% of the component from
the column.
Retention volume = Retention time ˣ Flow rate

35. Separation factor (S)
Ratio of partition co-efficient of the two
components to be separated.
If more difference in partition co-efficient b/w two
compounds, the peaks are far apart & S
Is more. If partition co-efficient of two compounds
are similar, then peaks are closer
Resolution (R)
The true separation of 2 consecutive peaks on
a chromatogram is measured by resolution
It is the measure of both column & solvent
efficiencies
R= 2d
W1+W2

36. Retention time

37. THEORETICAL PLATE
 An imaginary unit of the column where
equilibrium has been established between
S.P & M.P
 It can also be called as a functional unit of
the column
HETP – Height Equivalent to a Theoretical
Plate
 Efficiency of a column is expressed by the
number of theoretical plates in the column or
HETP
 If HETP is less, the column is ↑ efficient.
 If HETP is more, the column is ↓ efficient

38. Asymmetry Factor
 Chromatographic peak should be
symmetrical about its centre
 If peak is not symmetrical- shows Fronting or
Tailing
 FRONTING
Due to saturation of S.P & can be avoided by
using less quantity of sample
 TAILING
Due to more active adsorption sites & can be
eliminated by support pretreatment,

40. Applications of G.C
• G.C is capable of separating, detecting &
partially characterizing the organic
compounds , particularly when present in
small quantities.
1, Qualitative analysis
Rt & RV are used for the identification &
separation
2, Checking the purity of a compound
Compare the chromatogram of the std. & that
of the sample

41. 3, Quantitative analysis
It is necessary to measure the peak area or
peak height of each component
4, used for analysis of drugs & their
metabolites.

42. Advantages of Gas Chromatography
• Very good separation
• Time (analysis is short)
• Small sample is needed - l
• Good detection system
• Quantitatively analyzed