Gas chromatography its principle, instrumentation, advantages and disadvantages and application are widely covered in this presentation.

1. GAS CHROMATOGRAPHY
By-
Dipesh Adesh Gamare
Principle, Instrumentation, Advantage and disadvantage, applications
of Gas Chromatography

2. INTRODUCTION
• In gas chromatography, gas is the mobile phase and solid or liquid is the
stationary phase.
• Two techniques:-
1) Gas solid chromatography- Gas is used as the mobile phase and solid is used
as the stationary phase. Adsorption process takes place. Rarely used.
2) Gas liquid chromatography- Gas is used as the mobile phase and liquid, which
is immobilized by supporting on some solid matrix, is used as the stationary
phase. Partition process takes place. Widely used.

3. PRINCIPLE OF GLC
• The major role of the mobile phase is to push the solutes, which are desorbed from the
stationary phase, out of the column. Hence, the mobile phase is usually referred to as a
carrier gas.
• Sample should be in the form of vapor.
• Vapors of the sample is introduced at the head of the column.
• The solutes from the mixture interact with the stationary phase by dissolving in it.
• The solutes having greater solubility in the stationary liquid phase remain in the higher
concentration in it, whereas solutes having lesser solubility in the stationary liquid
phase remain in the smaller concentration in it. Thus, the solutes distribute themselves
between the phases according to their distribution coefficients.
• The solutes having lesser interaction with the stationary phase are easily desorbed
from it and are eluted out faster.
• The elution of the desorbed compounds is achieved by forcing an inert carrier gas
such as nitrogen or helium through the column.

4. INSTRUMENTATION OF GLC
1) Carrier gas supply
Soap bubble flow meter
• Soap bubbler flow meters are a classic method for measuring the gas
flow rate for carrier gases in applications such as gas chromatography
(GC).
• The unit is supplied with a rubber bulb which attaches to the bottom of
the device.
• The outlet of the system to be measured is connected to the serrated hose
connection (9 mm O.D. at the middle ring, 10 mm O.D. at the largest
ring), and the bulb is partially filled with soapy water.
• To make the measurement, the user squeezes the bulb until the soapy
water goes above the gas sidearm.
• This will cause a series of flat soap film bubbles to rise up the calibrated
column.
• Simply time how long it takes for the bubble to travel a given volume to
determine your flow rate.
• The column is open at the top and a clever projection at the top breaks
the bubbles automatically.
• This item is available in 10 and 25 mL sizes. The 10 mL has 0.05 mL
subdivisions and the 25 mL has 0.1 mL subdivisions.
• 10 mL dimensions: Overall length (without bulb): ~12-5/8" (322 mm).
Width at sidearm: ~3" (76 mm). Tube diameter: 7/16" (11 mm).
 Helium (He), nitrogen (N2), hydrogen
(H2), and argon (Ar) are often used.
 Helium and nitrogen are most commonly
used and the use of helium is desirable
when using a capillary column.
 Although expensive, it is safe and has a
relatively wide optimum linear velocity
range.

5. INSTRUMENTATION OF GLC
2) Sample injection system
• A sample of the suitable size should be introduced
as a ‘plug’ of vapor i.e. it should be introduced at
once.
• The slow injection or the oversized samples- poor
resolution.
• For injecting the sample into a heated sample port
located at the head of the column, a microsyringe
is used.
• The sample port is usually maintained at about 50
℃ above the boiling point of an analyte.
• Sample size- few tenths to 10 μL.
• Sample splitters.

6. INSTRUMENTATION OF GLC
3) Columns
Capillary columns/ Open tubular columns:-
• Capillary tubing of internal diameter- 0.3- 0.5 mm.
• Inner walls are coated with a very thin film of the liquid which acts as the stationary phase.
• It offers negligible resistance to the flow of the mobile phase hence pressure drop across the two
ends of the capillary column is negligible.
• Therefore, columns as long as 10-100 m or more can be used consists of several hundred
thousand theoretical plates.
• Vs/Vm= 100- 300- high efficiency.
• Limited amount of the stationary phase = very low sample loading capacity. Can be increased by
coating inner walls with porous material such as graphite, metal oxide or silicate. This will
increase the surface area for coating of the stationary phase which increases loading capacity.

7. INSTRUMENTATION OF GLC
Packed columns:-
• Glass or tubes of stainless steel, copper or aluminium, with the internal diameter 1- 8 mm.
• They are filled with solid supports, which adsorb liquid used as the stationary phase for the separation. The
packed stationary phase offers some resistance to the flow of the mobile phase hence there is some
pressure drop across the two ends of the column.
• Therefore not as long as the capillary columns; length is 2- 20 m.
• Vs/Vm= 10- 20.
• More amount of the stationary phase = high sample loading capacity.
• Low efficiency due to less number of theoretical plates (100-10000).
4) Thermostats/ temperature programming
• Sample in the form of vapor= column is operated at high temperature.
• Variation in temp. results in the change in the retention time of a compound.
• The optimum column temp. depends upon the B.P. of the sample to be analyzed and also on the degree of
separation required.

8. INSTRUMENTATION OF GLC
• A temperature programming facilitates controlled increase of even temperature during an analysis.
Thus, latter peaks also become sharp and emerge quickly. Thus in temp. programming the
components of a wide boiling range mixture may be resolved efficiently.
• Requirements for temp. programming:-
Dual column system- compensates for bleeding of liquid phase from columns during increase of temp.
Separate heaters for injector, column, oven, detectors.
Differential flow controllers.
Thin walled columns.
Pure dry carrier gas.
5) Detectors
6) Recorders

9. Electron capture detector
Principle :-
• A beam of electrons is generated from an electron emitter.
• These electrons generate a standing current in the circuit, which remains constant in absence of an organic compound.
• If an organic comp. comes in the path of this electron beam, suddenly the number of electrons decreased, and it results
in the change in the current in the circuit.
• This gives indication about the presence of an organic compound in the eluate and also about its conc. in it.
Advantages:-
 It is selective in its response.
 Highly sensitive towards the organic compounds possessing electronegative functional groups such as halogens,
peroxides, nitro, so on.
 Used for determination and detection of chlorinated insecticides.
 It does not alter the sample significantly.
Disadvantages:-
 Response is non- linear.

10. Electron capture detector

11. Flame ionization detector
CONSTRUCTION:-
• FID makes use of an oven, wherein flame is
produced by burning hydrogen gas in presence of
oxygen or air.
• A continuously moving wire loop is provided to
transport a portion of the eluate in the furnace.
• Two electrodes, anode (A) and cathode (C) are
placed on either side of a flame.
• A definite potential difference is maintained
across the two electrodes with the help of a series
of batteries.
• A amplifier and a recorder are included in the
circuitry for recording chromatograms.

12. Flame ionization detector
WORKING:-
• A continuously moving wire loop transports a
portion of the eluate coming out from the column
into the furnace, where the solvent is evaporated
first.
• Most organic compounds get pyrolyzed at the temp.
provided by hydrogen- air or hydrogen- oxygen
flame.
• Certain compounds are able to form ions after
pyrolysis. These ions are attracted either towards an
anode or a cathode, depending on the charge
present on them.
• The attraction of ions by the electrode results in the
change in the potential difference across the
electrodes, which in turn results in the change in the
current in the circuit.
• The electrical resistance of a flame is very high and
resulting current is therefore, minuscule. An
electrometer must be employed to measure small
magnitude of current accurately.

13. Flame ionization detector
Advantages :-
• Detects minute quantities of solutes hence very sensitive.
• It produces linear response over a wide range of concentration.
Disadvantages :-
• Complicated/ expensive.
• Destruction of the sample.

14. Thermal conductivity detector
Principle :-
• Based upon the changes in the thermal conductivity of the gas stream.
• Whetstone’s bridge, which consists of four resistances in the circuit, the magnitude of 3
resistances remains constant and the fourth one varies as per the change in the temperature
of the resistance wire.
• The change in the temperature of the resistance wire is because of the difference in the
thermal conductivities of the solute and the carrier gas when they are passed over the heated
element.
• This results in the change in the current in the circuit.
Advantages:-
Simple, rugged, inexpensive, broadly applicable detection system, non- destructive to the
sample, accurate results.
Disadvantages:-
Non- selective detector, not very sensitive.

15. Thermal conductivity detector

16. ADVANTAGES OF GAS CHROMATOGRAPHY
Gas chromatography (GC) is a widely used analytical technique in chemistry and related fields. It is a powerful
separation method that separates and analyzes mixtures of volatile compounds. Gas chromatography analysis offers
several advantages over other separation techniques, making it a popular choice for researchers and scientists.
Some of the advantages of gas chromatography analysis.
1. High sensitivity:
One of the significant advantages of gas chromatography is its high sensitivity. GC can detect even trace amounts of
compounds in a mixture, making it a powerful tool in analytical chemistry. The high sensitivity of GC is due to the
use of small sample sizes and the efficient separation of compounds.
2. High resolution:
GC can separate complex mixtures of compounds with high resolution. The resolution is the ability to distinguish
between two adjacent peaks in a chromatogram. The high resolution of GC is due to the use of narrow-bore capillary
columns and the ability to control the carrier gas flow rate.
3. Rapid analysis:
GC is a relatively fast analysis method, allowing for the analysis of multiple samples in a short time. This speed is
due to the use of narrow-bore columns that have a high surface area-to-volume ratio, allowing for the efficient
separation of compounds.

17. 4. Quantitative analysis:
GC can be used to perform quantitative analysis of compounds in a mixture. The area under a peak in a
chromatogram is proportional to the amount of the compound present in the sample, allowing for accurate
quantification of compounds in a mixture.
5. Minimal sample preparation:
GC requires minimal sample preparation compared to other analytical techniques, such as liquid chromatography.
This advantage is due to the volatile nature of the compounds analyzed by GC, which do not require complex
extraction or purification steps.
6. Cost-effective:
GC analysis is a relatively cost-effective technique compared to other analytical methods, making it accessible to
many researchers and scientists. The low cost of GC analysis is due to the availability of inexpensive equipment
and consumables.

18. DISADVANTAGES OF GAS CHROMATOGRAPHY
1.Gas chromatography is limited to volatile compounds.
2.Non-volatile compounds don't vaporize.
3.Analyte can decompose at high temperature.
4.Analyte can also react with stationary phase.
5.It is limited to low to medium molecular weight.
6.It is incompatible with aqueous samples.
7.Thermal stability is required during separation through gas chromatography.
8.It is not suitable for high-boiling compounds.
9.It is not sutable for polar analytes.

19. APPLICATIONS OF GAS CHROMATOGRAPHY
Gas chromatography offers many advantages, but what is it primarily used for? As we’ve said, gas chromatography’s versatility
makes it a favorite across many industries and applications, from food testing to meteorite analysis.
1) Food Analysis
Food analysis and quality control are one of the most common applications for gas chromatography due to their component
quantification, accuracy, and speedy process. Gas chromatography is used in the food industry both for quality control and for
accurate quantification of compounds and contaminants in food, such as:
 Carbohydrates
 Proteins
 Vitamins
 Lipids
 Steroids
 Pesticides
 Trace elements
With gas chromatography, food producers can accurately quantify the elements in their food, and the FDA ensures that it's of
sufficient quality and safety. Thanks to gas chromatography, consumers can purchase food at a grocery store with confidence that
it's been thoroughly tested for safety and that the food labels are accurate.
2) Environmental Monitoring
 Gas chromatography is also a popular method for ensuring that the air and water we breathe are safe for consumption. A huge
industry of scientists study our environment, and gas chromatography is a favored technique for detecting contaminants in the
environment—particularly those in the air.

20.  With gas chromatography, researchers can accurately determine the quality of the air and identify potentially harmful
chemicals in the air and where they might come from.
 Environmental regulators and organizations like the EPA commonly use gas chromatography to ensure air and water sources
aren’t contaminated.
3) Drug Testing
 Gas chromatography is also useful in identifying chemical compounds within the human body through the analysis of bodily
fluids. Gas chromatography is a quick and accurate drug testing method, which makes it a favored technique for things like
law enforcement; in fact, it’s been used to detect blood alcohol levels since the ‘50s.
 Gas chromatography can accurately identify and quantify alcohol or drug use in athletes. Sporting bodies like the Olympics
and
 With gas chromatography, forensic analysts can more accurately determine the circumstances of a person’s death and provide
that information to law enforcement.
4) Manufacturing Quality Control
 Another industry where gas chromatography is common in manufacturing. From automotive plants to pharmaceuticals, many
manufacturers use gas chromatography to test the quality and safety of their products.
 Pharmaceuticals must test the purity of the compounds within their drugs to ensure every batch is safe for consumption.
Automotive plants use gas chromatography to ensure there is no harmful chemicals leftover from the manufacturing process
that can harm humans within the vehicle.

21. 5) Forensics
 Gas chromatography provides the capable identification of compounds in bodily fluids, so it's also a favored method in
forensic analysis.
 Many forensic analysts use gas chromatography to determine a person's death by concluding whether they were poisoned,
intoxicated, or overdosed on a banned substance.
 With gas chromatography, forensic analysts can more accurately determine the circumstances of a person's death and provide
that information to law enforcement.
6) Environmental Research
 As we mentioned, environmental researchers use gas chromatography often, but it’s also favored by scientists examining
things from outside our world. Gas chromatography has even been commonly used to analyze and research meteorites that
have fallen to earth.
 With gas chromatography, scientists can accurately identify and quantify chemicals within objects from space, deepening our
understanding beyond our planet.

22. REFERENCES
1. Chatwal, G.R. and Anand, S.K.J. (2018) Instrumental Methods of Chemical Analysis. Himalaya Publishing House, Mumbai.
2. Kaur, G., & Sharma, S. (2018). Gas Chromatography -A brief review. ResearchGate.
https://www.researchgate.net/publication/344042922_Gas_Chromatography_-A_Brief_Review
3. Libretexts. (2023, August 29). Gas chromatography. Chemistry LibreTexts.
https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules_%28Analytical_Chemistry%29/Instru
mentation_and_Analysis/Chromatography/Gas_Chromatography
4. GenTech. (2023, March 27). Common Applications of Gas Chromatography | GenTech Scientific. GenTech Scientific.
https://gentechscientific.com/6-common-applications-of-gas-chromatography/
5. Advantages and Disadvantages of Gas Chromatography (GC). (2023.). https://www.pharmastuff4u.com/2023/03/advantages-
and-disadvantages-of-gas.html
6. Kumar, V. (2023, May 15). Advantages of gas chromatography Analysis. Infinita Lab.
https://infinitalab.com/blogs/advantages-of-gas-chromatography-analysis/
7. Soap Bubble Flowmeter. (2020). Safety Emporium. https://www.safetyemporium.com

23. THANK YOU !!!