GAS CHROMATOGRAPHY IN DETAIL WITH DETECTORS DEPARTMENT OF ANALYSIS

1. DEPARTMENT OF PHARMACEUTICAL ANALYSIS
PRESENTED BY
SHAGUFTA NISHAT

2. CONTENTS
S.NO TOPIC
1
2
3
4
5
6
7
8
INTRODUCTION
TYPES OF GC
PRINCIPLE
INSTRUMENTATION
WORKING
APPLICATIONS
CONCLUSION
REFERENCE

3. INTRODUCTION
 CHROMATOGRAPHY:
• The term chromatography is derived from two Greek words chromatos means
colour and graphien means write , “it is a technique employed for the separation
and analysis of complex mixtures by continuous distribution of the components
between two phases “namely
• stationary phase
• mobile phase
 GAS CHROMATOGRAPHY
• Gas chromatography ( GC) is a analytical technique that help to separate and
analyze a mixture of organic vapourizable or volatile compounds without their
decomposition
• The father of modern Gas Chromatography is Nobel prize winner JOHN PORTER
MARTIN
 THE TWO MAJOR TYPES of GC :
• Gas – solid chromatography
• Gas – liquid chromatography

4. Principle
• The principle of separation in GLC is
PARTITION.
• Gas is used as mobile phase. Liquid is used as
stationary phase.
• The component which is more soluble in
stationary phase and eluted slower the
component which is less soluble in stationary
phase travels faster and eluted out first
• Hence the components are separated
according to THREE PARTITION COEFFICIENT

5. Instrumentation for GC:

6. Carrier gas supply:
• It includes a cylinder which is filled with compressed gas
which act as mobile phase . the cylinder is fitted with a
pressure controller to control the pressure of gas
• The carrier gas must be chemically inert
• Commonly used gases include nitrogen, helium, argon &
carbon dioxide
• The choice of carrier gas is often dependant upon the type
of detector which is used
• It also contains a molecular sieve to remove water and
other impurities
• It is associated with the gas supply are gauges and flow
meters

7. Column unit:
• column is one of the important part of GC
which decides the separation efficiency.
• Column are made up of gas or stainless steel .
stainless steel column have the advantage of
long life and can be easily handled without
fear of fragility . But sample react with them .
Hence in such cases , glass column are use
Eg : steroids

8. Columns can be classified as:
• Depending on its use :
1. analytical column : analytical columns
have a length of 1-1.5m and an outer
diameter is 3-6mm
2. preparative column: preparative column are
larger when compared to analytical column.
They have length of 3-6m and outside
diameter of 6-9mm.

9. • Depending on its nature :
1. Packed column
2. Open tubular column / capillary column
3. SCOT(support coated open tubular
column)

10. Sample injector system
• The most common
method of injections
involves the use of a
micro-syringe to inject a
liquid or gaseous sample
through a silicone rubber
diaphragm or septum
into a flash vaporizer
port located at the
head of the column

11. Detectors
• The eluted solute particles along with the carrier gas
exit from the columns and enter the detector. The
detectors then produce electrical signals proportional
to the concentration of the components of solute .
• The signals are amplified and recorded as peaks at
intervals on the chromatograph
TYPES OF DETECTORS
• Flame ionization detector(FID)
• Thermal conductivity detector
• Electron capture detector
• Flame photometric detector

12. Characteristics of the ideal detector:
• It should be highly sensitive towards wide
range of compounds
• It should be stable during operation
conditions
• It should produce uniform and linear
responses towards wide range of vaporized
solute particles
• It should have concentration reproducibility
• It should be easy to operate

13. Flame ionization detector (FID):
• The FID is one of the
most widely used and
generally applicable
detectors for gas
chromatography. The
effluent from the
column is mixed with
hydrogen and air and
then ignited electrically
A diagram of a typical FID as shown in below

14. Thermal conductivity detector :
• A very early detector for gas
chromatography is based upon changes
in the thermal conductivity of the gas
stream brought about by the presence of
analyte molecules
• This device is sometimes called as
katharometer

15. Schematic of (a)a thermal conductivity detector cell
(b)an arrangement of two sample detector cells &two
reference detector cells
( from j.v hinshaw L.C –G.C, 1990, 8, 298, with
permission)

16. Electron capture detector :
• Electron – capture
detector (ECD) operates
in much the same way as
a proportional counter
for measurement of x
radiation. Here the
effluent from the column
passes over a beta –
emitter , such as nickel-
63 or tritium (adsorbed
on platinum or titanium
foil ). An electron from
the entire causes
ionization of the carrier
gas (often nitrogen) and
the production of a burst
electrons

17. Flame photometric detector:
• It is a selective detector that is responsive to
compounds containing sulphur or phosphorous
• It uses the luminous emissions of sulphur or
phosphorous from the eluent in a low
temperature hydrogen flame these emissions
serves as a tool for analytical information that is
specific for compounds bearing these atoms lmax
for species emitting sulphur is 394 nm while that
for species emitting phosphorous is 526nm the
intensity of these radiations is recorded
photometrically.

18. FPD diagram:

19. Working:
• In gas chromatography,
the carrier gas is the
mobile phase … the
sample being measured
is injected into the carrier
gas using a syringe and
instantly vaporizes . The
gases that make up the
sample separate out as
they move along the
column which is
stationary phase.

20. Applications:
 Qualitative analysis
 Quantitative analysis
 1.direct comparison method
 2. calibration curve method
 3. internal standard method
 Separation of fatty acids derived from fixed oils
 Inorganic compound analysis
 Dairy product analysis
 pollutants like formaldehyde, carbon mono oxide ,
benzene etc
 separation and identification of volatile oils

21. Complex mixture can be resolved into its components by this GC
Sensitivity in detection is very high with thermal conductivity
detectors .it can detect 100 ppm while other detectors can detect ppm
, parts per billion or picograms
It gives relatively good precision and accuracy
it is a micro method hence very small size is required hence micro
litre of sample is sufficient for complete analysis
The speed of analysis is very fast
Qualitative as well as quantitative analysis at a time is possible
The area produced for each peak is proportional to that
concentration
The cost of a gas chromatography is very low as compared to the
data obtained
Conclusion:

22. References:
1.S.RAVI SHANKAR ,Text book of pharmaceutical
analysis ,Rx publications,2001.pgno-17-1 to 17-20
2. http://www.cas.org
3. http://www.chemcentre/org
4. http://www.sciencemag.org
5.http://www.kerouac.pharm.uky.edu/asrg/wave/
wavehp.html
6. http://www.acs.org