Gas chromatography (GC)

1. Gas chromatography
Dr.Maryam kazemi
PhD student of pharmaceutics
Shiraz university of medical sciences

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3. Invention of Chromatography
Mikhail Tswett
Russian Botanist
(1872-1919)
Mikhail Tswett invented
chromatography in 1901
during his research on plant
pigments.
He used the technique to
separate various plant
pigments such as chlorophylls,
xanthophylls and carotenoids.
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• The father of modern
gas chromatography
is Nobel Prize winner
John Porter Martin,
who also developed
the first liquid-gas
chromatograph.
(1950)

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GC-MS
Quadri-
TOF

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7. Sample to be separated is converted into vapor
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:
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8. The organic compounds are separated due to
differences in their partitioning behavior
between the mobile gas phase and the
stationary phase in the column.
Principle
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10. GAS CHROMATOGRAPHY
GSC principle is ADSORPTION
GLC principle is PARTITION

11. Gas - Solid Chromatography (GSC)
 The stationary phase, in this case, is a solid like silica
or alumina.
 It is the affinity of solutes towards adsorption onto the
stationary phase which determines, in part, the
retention time.
 The mobile phase is, of course, a suitable carrier gas.
 Most useful for the separation and analysis of gases
like CH4, CO2, CO, ... etc.
 The use of GSC in practice is considered marginal
when compared to gas liquid chromatography.
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12. Gas - Liquid Chromatography (GLC)
 The stationary phase is a liquid with very low
volatility while the mobile phase is a suitable
carrier gas.
 GLC is the most widely used technique for
separation of volatile species.
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13. 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
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14. HETP= L (length of the column)
N(no of theoretical plates)
HETP is given by Van Deemter equation
HETP= A + B +Cu
u
A = Eddy diffusion term or multiple path diffusion
which arises due to packing of the column
B = Molecular diffusion, depends on flow rate
C = Effect of mass transfer, depends on flow rate
u = Flow rate
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15. Efficiency ( No. of Theoretical plates)
It can be determined by using the formula
n = 16 Rt2
w2
n = no. of theoretical plates
Rt = retention time
W = peak width at base
The no. of theoretical plates is high, the
column is highly efficient
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19. PRACTICAL REQUIREMENTS
• Carrier gas
• Flow regulators & Flow meters
• Injection devices
• Columns
• Temperature control devices
• Detectors
• Recorders & Integrators
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Syringe
Injector
Detector
Carrier Gas Cylinder Column
To Waste or Flow Meter
Flow Controller
Two-Stage
Regulator

21. 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
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22. CARRIER GAS
» Hydrogen ( H2 )
better thermal conductivity
Disadvantage: it reacts with unsaturated
compounds & inflammable
» Helium ( He)
excellent thermal conductivity
it is expensive
» Nitrogen ( N2)
reduced sensitivity
it is inexpensive
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23. 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
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25. Soap Bubble Meter
◊ Similar to Rota meter & instead of a float, soap bubble
formed indicates the flow rate
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27. Injectors
 Septum type injectors are the most common.
 These are composed of a glass tube where vaporization of
the sample takes place.
 The sample is introduced into the injector through a self-
sealing silicone rubber septum.
 The carrier gas flows through the injector carrying
vaporized solutes.
 The temperature of the injector should be adjusted so
that flash vaporization of all solutes occurs. If the
temperature of the injector is not high enough (at least
50 degrees above highest boiling component), band
broadening will take place.
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Carrier
Gas
Syringe
Vaporization
Chamber
To
Column
Septum

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Split-splitless Injector
Split-splitless injectors are used for introduction of highly concentrated
samples into capillary columns. Sample is volatilized by injection into a heated
glass liner. The carrier gas then either sweeps the total sample (Splitless mode)
or a portion (Split mode) into the column. The split vent controls the amount
of sample entering and the other portion is exhausted. This mode is useful for
highly concentrated or dirty samples. It helps in producing narrow band
widths. Split-less injection is useful for trace level analysis.

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40. Head space injection
• Simple Definition
• 'Headspace' is the gas space above the sample
in a chromatography vial. Volatile sample
components diffuse into the gas phase,
forming the headspace gas. Headspace
analysis is therefore the analysis of the
components present in that gas.
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Gas Chromatographic Columns and
Stationary Phases
Packed Columns
These columns are fabricated from glass, stainless steel,
copper, or other suitable tubes.
Stainless steel is the most common tubing used with internal
diameters from 1-4 mm.
The column is packed with finely divided particles (<100-300
mm diameter), which is coated with stationary phase.
However, glass tubes are also used for large-scale
separations.

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47. Capillary/Open Tubular
Open tubular or capillary columns are finding broad
applications. These are mainly of two types:
• Wall-coated open tubular (WCOT)
Internal wall of capillary is coated with a very fine film of liquid
stationary phase.
These are used for fast and efficient separations but are good
only for small samples. The most frequently used capillary
column, nowadays, is the fused silica open tubular column
(FSOT), which is a WCOT column.
• Support-coated open tubular (SCOT)
and related PLOT columns(porous layer open tubular columns)
Capillary tube wall is lined with a thin layer of solid support on
to which liquid phase is adsorbed. The separation efficiency
of SCOT columns is more than WCOT columns because of
increased surface area of the stationary phase coating.
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48.  The external surface of the fused silica columns is
coated with a polyimide film to increase their
strength and to protect the silic from atmospheric
degradation.
 The most frequently used internal diameters occur in
the range from 260-320 micrometer.
 However, other larger diameters are known where a
530 micrometer fused silica open tubular column was
recently made and is called a megapore column, to
distinguish it from other capillary columns.
Megapore columns tolerate a larger sample size.
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54. A gas chromatography oven, open to show a
capillary column
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57. It should be noted that since capillary columns are
not packed with any solid support, but rather a
very thin film of stationary phase which adheres
to the internal surface of the tubing, the A term
( Eddy’s diffusion co-efficient)in the van
Deemter equation which stands for multiple
path effects is zero and the equation for
capillary columns becomes
H = B/V + CV
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59. Capillary columns advantages compared to packed
columns
1. higher resolution
2. shorter analysis times
3. greater sensitivity
Capillary columns disadvantage compared to
packed columns
1. smaller sample capacity
2. Need better experience
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60. Solid Support Materials
The solid support should ideally have the following
properties:
1. Large surface area (at least 1 m2/g)
2. Has a good mechanical stability
3. Thermally stable
4. Inert surface in order to simplify retention behavior and
prevent solute adsorption
5. Has a particle size in the range from 100-400 mm
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61. Selection of Stationary Phases
 General properties of a good liquid stationary phase
are easy to guess where inertness towards solutes is
essential.
 Very low volatility liquids that have good absolute
and differential solubilities for analytes are required
for successful separations.
 An additional factor that influences the performance
of a stationary phase is its thermal stability where a
stationary phase should be thermally stable in order
to obtain reproducible results.
 Nonvolatile liquids assure minimum bleeding of the
stationary phase
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62.  Generally, the film thickness primarily affects the retention
character and the sample capacity of a column.
 Thick films are used with highly volatile analytes, because
such films retain solutes for a longer time and thus provide
a greater time for separation to take place.
 Thin films are useful for separating species of low
volatility in a reasonable time.
 A thicker film can tolerate a larger sample size.
 Film thicknesses in the range from 0.1 – 5 mm are
common.
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63. Liquid Stationary Phases
 In general, the polarity of the stationary phase
should match that of the sample constituents
("like" dissolves "like").
 Most stationary phases are based on
polydimethylsiloxane or polyethylene glycol
(PEG) backbones:
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66. Much more efficient separations can be
achieved with capillary columns, as
compared to packed columns, due to the
following reasons:
1. Very long capillary columns can be used
which increases efficiency
2. Thinner stationary phase films can be used
with capillary columns
3. No Eddy diffusion term (multiple paths
effect) is observed in capillary columns
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