Gas chromatography 1. By Pratik P. Shinde (M.Pharm ) 2. Index 3. Gas chromatography- It is a common type of chromatography used in analytical chemistry for separating and analyzing compounds that can be vaporized without decomposition. In gas chromatography, the mobile phase is a carrier gas, usually an inert gas such as helium or an unreactive gas such as nitrogen It has two types Gas-liquid chromatography: The mobile phase is a gas and the stationary phase is a thin layer of a non volatile liquid bound to solid support. A partition process occurs Gas- solid chromatography: The mobile phase is a gas and the stationary phase is a solid adsorbent and adsorption process take place 4. Principle: The component which is more soluble in stationary phase travel slower and eluted later. The component which is less soluble in stationary phase travels faster and eluted out first. Gas-liquid chromatography: The components of mixture distribute themselves between gas phase and the stationary liquid phase according to their partition coefficients. Gas- solid chromatography: The components of mixture distribute themselves between gas phase and the stationary adsorbent and the separation is due to the differences in adsorptive behaviour. 5. Instrumentation: Carrier gas - He (common), N2, H2, Argon Gas regulator Sample injection port - micro syringe Columns Packed Capillary Detectors Thermal conductivity (TCD) Electron capture detector(ECD) Flame Ionization detector (FID) Flame photometric (FPD) Recorder 6. 7. Carrier gas: Carrier gas used in gas chromatography should meet the following criteria: The pressure of gas should be between 40-80psi. It should be chemically inert. It should be cheap and readily available. It should be of high quality and not cause any fire accident. It should be suitable for the sample to be analyzed and for the detector. Commonly use gases include Helium, nitrogen, hydrogen and carbon dioxide. 8. Helium (He): Good thermal conductivity Low density Inert but expensive Flow rate : 25 -150 mL/min for packed columns Flow rate: 2-25 mL/min for open tubular column Inlet pressure ranges from 10-50psi Nitrogen: Inexpensive Easily available Hydrogen: Low density Easily available React with unsaturated compound Carbon-dioxide and Argon: 9. Gas purification and filtration: Filters and traps: Traps help remove moisture, oxygen, hydrocarbons and other impurities from gas lines. Metal or glass traps are commonly used. Plastic traps like plastic tubes are not recommended. Traps are available with standard 1/4”or 1/8” compression fittings. Moisture traps: are generally self indicating type and packed with molecular sieves or silica gel which will reduce both oxygen and moisture to less than 15 ppb. Hydrocarbon traps are useful for removing hydrocarbon impurities by absorption on activated charcoal. A 20 μm frit removes particulate impurities.

1. University Department of Pharmaceutical Sciences
Rashtrasant Tukadoji Maharaj Nagpur University, Nagpur 2021-2022
GAS CHROMATOGRAPHY
27-08-2022
Presented by
Mr. Pratik P. Shinde
M. Pharm
(Pharmaceutics)

2. Index
2
Sr.
no.
Topic Page No.
1. Introduction 3
2. Principle 4
3. Instrumentation 5 – 6
4. Carrier gas 7 - 10
7. Sample injection 11 - 13
8. Column 14 - 17
9. Detector 18 - 23
11. Application 24
12. References 25

3. Introduction
Gas chromatography- It is a common type of chromatography used
in analytical chemistry for separating and analyzing compounds that can
be vaporized without decomposition. In gas chromatography, the mobile
phase is a carrier gas, usually an inert gas such as helium or
an unreactive gas such as nitrogen
It has two types
 Gas-liquid chromatography: The mobile phase is a gas and the
stationary phase is a thin layer of a non volatile liquid bound to solid
support. A partition process occurs
 Gas- solid chromatography: The mobile phase is a gas and the
stationary phase is a solid adsorbent and adsorption process take place
3

4. Principle
The component which is more soluble in stationary phase travel slower
and eluted later. The component which is less soluble in stationary phase
travels faster and eluted out first.
 Gas-liquid chromatography: The components of mixture distribute
themselves between gas phase and the stationary liquid phase according
to their partition coefficients.
 Gas- solid chromatography: The components of mixture distribute
themselves between gas phase and the stationary adsorbent and the
separation is due to the differences in adsorptive behaviour.
4

5. Instrumentation
I. Carrier gas - He (common), N2, H2, Argon
II. Gas regulator
III. Sample injection port - micro syringe
IV. Columns
1. Packed
2. Capillary
V. Detectors
1. Thermal conductivity (TCD)
2. Electron capture detector(ECD)
3. Flame Ionization detector (FID)
4. Flame photometric (FPD)
VI. Recorder
5

6. 6

7. Carrier gas
Carrier gas used in gas chromatography should meet the following
criteria:
The pressure of gas should be between 40-80psi.
It should be chemically inert.
It should be cheap and readily available.
It should be of high quality and not cause any fire accident.
It should be suitable for the sample to be analyzed and for the
detector.
Commonly use gases include Helium, nitrogen, hydrogen and
carbon dioxide.
7

8. Various example of carrier gases are as discussed bellowed
1. Helium (He):
 Good thermal conductivity
 Low density
 Inert but expensive
 Flow rate : 25 -150 mL/min for packed columns
 Flow rate: 2-25 mL/min for open tubular column
 Inlet pressure ranges from 10-50psi
2. Nitrogen:
 Inexpensive
 Easily available
3. Hydrogen:
 Low density
 Easily available
 React with unsaturated compound
4. Carbon-dioxide and Argon:
8

9.  Filters and traps: Traps help remove moisture, oxygen, hydrocarbons and other
impurities from gas lines. Metal or glass traps are commonly used. Plastic traps
like plastic tubes are not recommended. Traps are available with standard 1/4”or
1/8” compression fittings.
 Moisture traps: are generally self indicating type and packed with molecular
sieves or silica gel which will reduce both oxygen and moisture to less than 15 ppb.
 Hydrocarbon traps are useful for removing hydrocarbon impurities by
absorption on activated charcoal. A 20 μm frit removes particulate impurities.
Indicating hydrocarbon traps are used for removal of oil contamination from oil
lubricated air compressors for FID operation.
 Oxygen traps remove oxygen down to 0.1 ppm.Oxygen contamination can
produce excessive column bleed at high temperatures. Care needs to be exercised in
handling oxygen traps as these are packed with highly reactive material whose
exposure should be avoided.
9
Gas purification and filtration

10. Gas traps
10

11. Sample injection
 Sampling unit or injection port is attached to the column head.
 Since the sample should be in vaporized state, the injection port is
provided with an oven that helps to maintain its temperature at about 20-
500 C above the boiling point of the sample.
 Gaseous samples may be introduced by use of a gas tight hypodermic
needle of 0.5-10 ml capacity.
 For Liquid samples , micro syringes of 0.1-100µL capacity may be
used.
11

12. Temperature programmed
Gas chromatography
 (TPGC) is the process of increasing the column temperature during a run. It
was developed by Steve dal Nogare of du Pont.
 Temperature directly affects the tendency of organic compounds to enter the gas
phase and therefore affects K, the distribution coefficient.
 If the boiling point is high, then compound spend most of time in stationary
phase and the GC peak is very broadened
 Temperature programming permits the higher resolution of lighter
compounds and sharp peaks for heavier compounds, reducing the long run times
generated by heavier compounds
 In this method sample is injected in normal way. The temperature of column is
maintain at some suitable low temperature, such as 50°C, during injection.
 The column temperature is then increased at controlled rate(eg 20 °C/min) upto
maximum temperature high as 300°C.
12

13. Higher temperature not use it may lost substrate and destroy detector
 It is noted that column may be at low temperature initially, the inlet port
must be maintained at high temperature 350°C to ensure rapid
vaporization of sample after injection
13

14. Columns
Columns are of different shapes and sizes that includes: “U” tube type or coiled helix
type. They are mainly made of copper, stainless steel, aluminum, Glass, nylon and
other synthetic plastics.
There are two general types of columns:
1. Packed column:
For GSC the columns are packed with size graded adsorbent or porous .
. polymer, whereas for GLC the packing is prepared by coting the liquid phase .
. over a size graded inert solid support.
2. Capillary column:
It is mainly of two types:
 Wall-coated columns - consist of a capillary tube whose walls are coated with
liquid stationary phase.
 Support-coated columns- the inner wall of the capillary is lined with a thin
layer of support material such as diatomaceous earth, onto which the liquid
stationary phase has been adsorbed. It is also known as PLOT (porous-layer
open tubular columns).
14

15. Packed SCOT WCOT
Typical inside diameter 2-4mm 0.50mm 0.25-0.50mm
Typical length 1-4m 10-100m 10-100m
Typical efficiency 500-1000 plates/meter 600-1200 plates/meter 1000-3000 plates/meter
Sample size 10ng-1mg 10ng-1ug
Pressure require high Low Low
15
Wall coated open tubular
(WCOT)
Support coated open tubular
(WCOT)
Liquid
phase
Column
wall
Solid support
coated with
liquid phase
Porous layer open tubular
(PLOT)

16. Stationary phases
Abbreviation Identification
1. Carbowax Polyethylene glycols
2. CDMS Cyclohexane dimethanol succinate
3. DEGS Diethylene glycol succinate
4. Dexil 300 Carborane- silicone
5. OV 1 Methyl silicone
6. Polysiloxanes Silicone oils and gum
7. FFAP Free fatty acid phase
16

17. Thermal Conductivity Detector
 This is also known as katharometer or hot
wire detector.
 When an analyte species flows past the
filament generally thermal conductivity
changes, thus resistance changes which is
sensed by Wheatstone bridge arrangement.
 The imbalance between control and sample
filament temperature is measured and a
signal is recorded
 Universal detector
 Simple and inexpensive
 Disadvantage
 Low sensitivity
 Affected by fluctuation of temperature and
flow rate
17
Power
supply
Zero Control
Recorder
Detector
block
Pure carrier gas
from reference
column
Sample + carrier
gas from analytic
column
Detector

18. Flame Ionization Detector
 A flame of hydrogen is maintained at a
capillary jet made of quartz or platinum, air
or oxygen is introduce through a side by
inlet for supporting the combustion.
 Column effluents are led into the flame
where the ionization of component may
takes place.
 Electrode system located close by pick up
the ionization current which is then
amplified and fed to recorder.
 It is sensitive to almost all organic
compound
18
Power
supply
Zero Control
Recorder
Detector
block
Pure carrier gas
from reference
column
Sample + carrier
gas from analytic
column
Collector
electrode
+300
polarising
volts

19. Electron Capture Detector
 It responds to only those compounds whose
molecule has affinity for electrons, eg
chlorinated compound, unsaturated
compound
 A tritium or Ni63 foil placed inside the cell
ionize the carrier gas molecule thus standing
current is produce
 When a component having affinity for
electrons elutes out of the column and enters
the detector, it absorbed some electron
causing drop in standing current
 This loss of current is traced by recorder as
peak
 Temperature limitation(220C)
 Required pure nitrogen and argon-methane
gas mixture as carrier gas
19
Power
supply
Zero Control
Recorder
Detector
block
Pure carrier gas
from reference
column
Sample + carrier
gas from analytic
column

20. Flame Photometric Detector
20
Power
supply
Zero Control
Recorder
Detector
block
Pure carrier gas
from reference
column
Sample + carrier
gas from analytic
column
 It is a selective detector that is responsive to
compounds containing sulphur or phosphorous
 The detection principle is the formation of excited
sulphur (S2*) and excited hydrogen phosphorous
oxide species (HPO*) in a reducing flame.
 A photomultiplier tube measures the characteristic
chemiluminescent emission from these species.
 The optical filter can be changed to allow the
photomultiplier to view light of 394 nm for sulphur
measurement or 526 nm for phosphorus.
 Applications:
1. For detection of heavy metals like chromium,
selenium, tin, etc, in organometallic compounds.
2. Also for analysis of pesticides, coal, hydrogenated
products as well as air and water pollutants.

21. Parameters of GC
21
 Retention Time: defined as the absolute time taken by a sample to show maximum peak
after injecting.
 Retention Volume: defined as the volume of gas required to elute about half of the
solute through the column.
VR = tR ×F
F =average volumetric flow rate (mL/min)
 HETP (height equivalent to theoretical plate)- It is the distance on the column in which
equilibrium is attained between the solute in the gas phase and the solute in liquid phase.
Larger the number of theoretical plates/ smaller the HETP, the more efficient the column
is for separation.
HETP = L/n
Where, n = number of theoretical plates,
L = Length of column

22.  Van Demeter equation
HETP=A + B/u + Cu
HETP measure of the resolving power of the column [m]
Where, A = Eddy-diffusion parameter, related to channeling through a non-ideal
. packing [m]
B = diffusion coefficient of the eluting particles in the longitudinal direction,
. resulting in dispersion [m2 s−1]
C = Resistance to mass transfer coefficient of the analyte between mobile and
. stationary phase [s]
u = speed [m s−1]
22

23. Factors affecting retention time
23
 Boiling point : If a component has low boiling point then it is likely to spend more time
in gas phase. Therefore its retention time will be lower than a compound with a higher
boiling point.
 Column temperature: A high column temperature will give shorter retention times, as
more component stay in the gas phase.
 Carrier gas flow- rate : A high flow rate lower retention times but also yields poor
separation
 Column length: A longer column will produce longer retention time but better
separation . But if component has too long a transit time in column, there can be
diffusive effect that can causes the peak width to broaden.
 Polarity: If the polarity of compound and sample is similar then there is increase in
retention time.

24. Application
 Qualitative Analysis – by comparing the retention time or volume of
the sample to the standard / by collecting the individual components as
they emerge from the chromatograph and identifying these compounds
by other methods like UV, IR, NMR.
 Quantitative Analysis- area under a single component elution peak is
proportional to the quantity of the detected component/response factor of
the detectors.
Application in pharmaceutical analysis
 Antibiotic: Penicillin, gentamycin, kanamycin
 Anti TB drugs: Ethambutol
 Antiviral: amantadine
24

25. References
1. A.V.Kasture; pharmaceutical analysis- volume II.
2. Instrumental Methods of Chemical Analysis; Gurdeep R. Chatwal,
page no. 2.674-2.700
3. Chemical Analysis, modern instrumentation Method and
techniques, second edition, Francis rouessac and Annick Rouessac,
university of le Mans, Fracne, page no. 31-61
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26. Thank you
26