This Presentaion on Gas chromatography

1. GAS CHROMATOGRAPHY
PRESENTD BY- GUIDED BY-
Mr.Mayur R. Wagh Prof. Mr. M. T. Mohite
(M.Pharm First Sem.)
-Pharmaceutics
Department OF Pharmaceutics
Dr. D. Y. Patil College Of Pharmacy, Akurdi, Pune-44
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2. Contents:-
 Introduction
 Principle
 Instrumentation
 Detectors
 Applications
 References
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3. Introduction:-
Modern gas chromatography (GC) was
invented by Martin and James in 1952.
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4.  Principle of GC-
 The organic compounds are separated due to
differences in their partitioning behavior between the
mobile gas phase and the stationary phase in the
column.
 The sample solution injected into the instrument
enters a gas stream which transports the sample
into a separation tube known as the "column.“
 The detector measures the quantity of the
components that exit the column.
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5. Mobile Phase in GC-
In gas chromatography, the mobile phase (or
"moving phase") is a carrier gas, usually an inert gas.
such as helium, argon or an unreactive gas such
as nitrogen.
Stationary Phase in GC-
Here, the principle of “like dissolves like” applies,
where “like” refers to the polarities of the solute and
the immobilized liquid.
 e.g. Dimethyl Polysiloxane, Polyethylene Glycol.
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6. • Instrumentation-
1.Gas source (carrier gas)
2. Injector or sample application system (sample inlet)
3. Chromatographic column (with oven for temperature control)
4. Detector & recorder
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Flow meter
Gas
supply
Pressure
regulator
Flow
controller
Septum Detector
Oven
Column
Injector
GC
Chart
RecorderΟ

7. 1.Carrier gas-supply-
 Carrier gases serve to produce wind through the
column to move our solutes forward.
 Carrier gases, which must be chemically inert.
 E.g. Helium, nitrogen, and hydrogen.
2.Sample Injection System-
The most common method of sample injection involves
the use of microsyringe to inject a liquid or gaseous
sample.
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8. 3.Columns
Columns vary in length from less than 2 m to 50 m or more.
They are constructed of stainless steel, glass, fused silica.
Two general types of columns are-
1.Packed column-
.
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Packed columns are made of a glass or a metal
tubing which is densely packed with a solid
support like diatomaceous earth. Due to the
difficulty of packing the tubing uniformly, these
types of columns have a larger diameter than
open tubular columns and have a limited range
of length. As a result, packed columns can only
achieve about 50% of the efficiency of a
comparable WCOT column. Furthermore, the
diatomaceous earth packing is deactivated
over time due to the semi-permanent adsorption
of impurities within the column.
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9. 2.Open tubuler column-
When the stationary phase is uniformly distributed on the interior
surface of column it is called an open tubular (capillary) column.
Open tubular columns are longer, smaller in diameter, and more
efficient than packed columns. Open tubular columns have less
flow resistance which allows for them to be longer and have a lot of
theoretical plates. Capillary columns are between 3 and 100 meters
long and form a helical shape. The most common stationary phases
used for open tubular columns are polysiloxanes.
Types of Open tubular column-
1.WCOT
2.SCOT
3.PLOT
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10. 1.Wall-coated open tubular column-:
In 1957, Golay demonstrated the superiority of wall-coated open
tubular (WCOT) columns (a 100-fold or higher increase in
efficiency) relative to packed columns; yet, it took a quarter
century before this efficiency was realized in practice. In WCOT
columns, the wall is directly coated with the stationary-phase layer
at a film thickness of 0.05–3 μm.
2. Support-Coated Open Tubular Column-:
These columns contain an adsorbed layer of a very fine solid support
(such as Celite) coated with the liquid phase. SCOT columns can
hold more liquid phase and have a higher sample capacity than
the thin films of early wall-coated open tubular (WCOT) columns
had. With the introduction of cross-linking techniques, the use of
stable, thick films in WCOT columns has become possible, thereby
making SCOT columns redundant.
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11. 3.Porous Layer Open Tubular Column-:
Porous layer open tubular (PLOT) columns, first suggested by Golay in
the late 1950s, have been successfully developed and commercialized.
PLOT columns contain a porous layer of a solid adsorbent such as
alumina, molecular sieves, or Porapak. PLOT columns are well suited for
the analysis of light, fixed gases, and other volatile compounds
4.Column Ovens-
The optimum column temperature depends upon the boiling point of
the sample and the degree of separation.
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12. 5.Detectors-
Characteristics of the Ideal Detector:
1. Adequate sensitivity
2. Good stability and reproducibility.
3. Nondestructive of sample
4. High reliability and ease of use.
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13. Types Of Detectors- 13

14. 1.Flame Ionization Detectors (FID)
The flame ionization detector is the most widely
used detectors.
 ADV.- Responds to all organic compounds
The effluent from the column is mixed with
hydrogen and air and then ignited electrically
Organic compounds burning in the flame
produce ions & electrons which can conduct
electricity through the flame
Ions attracts towards electrode and ionisation
of sample takes place.
The current resulting from the pyrolysis of any
organic compounds is amplified by amplifier&
the output fed to a data to recorder.
Working-
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15. 2.Thermal Conductivity Detectors(TCD)
 TCD is based upon changes in the thermal
conductivity of the gas stream brought about by the
presence of analyte molecules.
 The heated element may be a fine platinum, gold, or
tungsten wire or a semiconducting thermist.
 The device contains an electrically heated source
whose temperature at constant electrical power
depends on the thermal conductivity of the surrounding
gas.
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16. The thermal conductivities of helium and hydrogen
(commonly used carrier gases for TCD) are roughly 6~10
times greater than those of most organic compounds.
Thus, even small amounts of organic species cause
relatively large decreases in the thermal conductivity of
the column effluent, which results in a marked rise in the
temperature of the detector.
Advantages:
• Simplicity, large linear dynamic range, nondestructive.
Disadvantages:
•Low sensitivity (precludes their use with WCOT columns
with small amounts of sample).
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17. 3.Electron-Capture Detectors(ECD)
 Radioactive decay-based detector.
 Selective for compounds containing
electronegative atoms, such as halogens,
peroxides, quinones, and nitro groups.
 The sample effluent from a column is
passed over a radioactive β emitter,
usually 63Ni. An electron from the emitter
causes ionization of the carrier gas (often
N2) and the production of a burst of
electrons.
 In the absence of organic species, a
constant standing current between a pair
of electrode results from this ionization
process. The current decreases significantly
in the presence of organic molecules
containing electron negative functional
groups that tend to capture electrons.
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18.  Advantages:
 useful for environmental testing
 detection of chlorinated pesticides or herbicides.
 aromatic carcinogens, organometallic compounds
 selective for halogen- (I, Br, Cl, F), nitro-, and sulfur-
containing compounds.
 Disadvantages:
 It is insensitive to functional groups such as amines,
alcohols, and hydrocarbons.
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19. 4.Nitrogen-phosphorus Detectors
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 The nitrogen–phosphorus detector (NPD) is also known
as thermionic specific detector.
 In which thermal energy is used to ionize an analyte.
 In this method, nitrogen and phosphorus can be
selectively detected with a sensitivity that is 104
times
greater than that for carbon.

20. Working-:
 A concentration of hydrogen gas is used such that it is just
below the minimum required for ignition.
 A rubidium or cesium bead, which is mounted over the
nozzle, ignites the hydrogen (by acting catalytically), and
forms a cold plasma.
 Excitation of the alkali metal results in ejection of electrons,
which in turn are detected as a current flow between an
anode and cathode in the chamber.
 As nitrogen or phosphorus analytes exit the column, they
cause a reduction in the work function of the metal bead,
resulting in an increase in current.
 ADV.- High sensitivity, specific towards nitrogen and
phosphorus.
 Disadv.- Performance deteriorates with time.
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21. Applications of GC-
1.Qualitative Analysis-
Gas chromatograms are widely used as criteria of
purity for organic compounds. Contaminants, if
present, are revealed by the appearance of
additional peaks.
The technique is also useful for evaluating the
effectiveness of purification procedures.
Gas chromatography provides an excellent means of
confirming the presence or absence of a suspected
compound in a mixture.
2.Quantitative Analysis-
-Calibration of standards
-The internal standard method
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23. THANK YOU…
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