Gas chromatography

Components, Advantages and Applications of Gas Chromatography

1. GAS
CHROMATOGRAPHY
(PAPER IV- ANALYTICAL)
-Jaiswal Priyanka Balister
MSc-I

2. Contents
•Introduction
• Principle
•How a Gas Chromatography Machine Works
•Components of Gas chromatography
•Column temperature and
temperature programming
•Parameters used in GC
•Advantages of Gas Chromatography
•Applications of Gas Chromatography
•Bibliography

3. Introduction
•The father of modern gas chromatography is Nobel Prize winner John
Porter Martin, who also developed the first liquid-gas chromatograph.
(1950)
•It involves separation of gaseous & volatile substances .
•It is simple & efficient in regard to separation
•Two major types :
• Gas-solid chromatography
• Gas-liquid chromatography

4. •Mobile Phase – Gas
•Stationary Phase – Solid (GSC) & Liquid (GLC)
•Principle of Gas solid chromatography is ADSORPTION.
•Principle of Gas liquid chromatography is PARTITION.
•GLC is more commonly used.
•GSC is not used often due to limited number of available
stationary phases.

5. Principle
•Sample to be separated is converted into vapour.
•It then gets mixed with gaseous Mobile phase.
•Component more soluble in the stationary phase → travels
slower.
•Component less soluble in the stationary phase → travels
faster .
•Components are separated according to their Partition Co-
efficient.

6. Criteria for compounds to be
analyzed by G.C
•Compounds for analysis by Gas chromatography must be volatile
enough to be amenable to GC.
•It must also be thermally stable to survive the extended time the
sample must spend in the gas phase.

7. How a Gas Chromatography Machine
Works
•First, a vaporized sample is injected onto the chromatographic
column.
•Second, the sample moves through the column through the flow of
inert gas.
•Third, the components are recorded as a sequence of peaks as they
leave the column.

8. Chromatographic Analysis
•The number of components in a sample is determined by the
number of peaks.
•The amount of a given component in a sample is determined by the
area under the peaks.
•The identity of components can be determined by the given
retention times.

9. Peaks and Data

10. •Components of Gas chromatography
•Carrier gas
•Flow regulators & Flow meters
•Sample injection port
•Columns
•Temperature control devices
•Detectors
•Recorders

11. Schematic diagram of a gas
chromatogram

12. Carrier gas
• Commonly used gases include nitrogen, helium, argon, and carbon
dioxide.
•Hydrogen :
better thermal conductivity
Disadvantage: It reacts with unsaturated compounds & is
inflammable.
•Helium :
excellent thermal conductivity
It is expensive
•Nitrogen :
reduced sensitivity
It is inexpensive

13. 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

14. Flow regulators & Flow meters
•To 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
•Soap Bubble Meter
Similar to Rota meter & instead of a float, soap bubble
formed indicates the flow rate.

15. Soap bubble meter and Rota meter

16. Sample injection- Direct Injection
•Gases can be introduced
into the column by valve
devices.
•Liquids can be injected
through loop or septum
devices.

17. Sample injection- rotary sample valve with
sample loop
•Split injection : routine method
- 0.1-1 % sample to column
- remainder to waste
•Split less injection : all sample to column
- best for quantitative analysis
- only for trace analysis, low [sample]
•On-column injection :
-for samples that decompose above boiling
point ( no heated injection port)
-column at low temperature to condense
sample in narrow band
-heating of column starts chromatography

18. Gas Chromatography - Columns
•Two general types of column : packed and capillary ( open tubular).
•Packed columns contain a finely divided, inert, solid support material
( diatomaceous earth) coated with liquid stationary phase. Most packed
columns are 1.5 - 10m in length and have an internal diameter of 2 - 4mm.
•Capillary columns have an internal diameter of a few tenths of a
millimeter. They can be one of two types; wall-coated open
tubular (WCOT) or support-coated open tubular (SCOT).
- WCOT columns consist of a capillary tube whose walls are coated
with liquid stationary phase. In 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 stationary phase has been adsorbed.
- SCOT columns are generally less efficient than WCOT columns. Both
types of capillary column are more efficient than packed columns.

19. G C - DETECTORS
•There are many detectors which can be used in gas chromatography.
• Different detectors will give different types of selectivity.
•Detectors : concentration dependant detectors and mass flow
dependant detectors.
•The signal from a concentration dependant detector is related to the
concentration of solute in the detector, and does not usually destroy the
sample Dilution of with make-up gas will lower the detectors response.
•Mass flow dependant detectors usually destroy the sample, and the
signal is related to the rate at which solute molecules enter the
detector. The response of a mass flow dependant detector is unaffected
by make-up gas

20. G C – IDEAL DETECTORS
• Sensitive (10
-8
-10
-15
g solute/s)
• Operate at high T (0-400 °C)
• Stable and reproducible
• Linear response
• Wide dynamic range
• Fast response
• Simple (reliable)
• Nondestructive
• Uniform response to all analytes

21. Column temperature and
temperature programming
•The column(s) in a GC are contained in an oven, the temperature of
which is precisely controlled electronically.
•The rate at which a sample passes through the column is directly
proportional to the temperature of the column. The higher the column
temperature, the faster the sample moves through the column.
•A method which holds the column at the same temperature for the
entire analysis is called “Isothermal Programming“
•Most methods, however, increase the column temperature during the
analysis.
•" Gradient Temperature Programming” - Start at low temperature and
gradually ramp to higher temperature.

22. Parameters used in GC
•Retention time (Rt) : It is the difference in time b/w the point of
injection & appearance of peak maxima. Rt measured in minutes or
Seconds
•Retention volume (Vr) : It is the volume of carrier gas which is
required to elute 50% of the component from the column.
Retention volume = Retention time Flow rate
ˣ
•Separation factor (S) : Ratio of partition co-efficient of the two
components to be separated.
•Resolution (R) : The true separation of 2 consecutive peaks on a
chromatogram is measured by resolution. It is the measure of both
column & solvent efficiencies.
•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.

23. 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 less, the column is ↓ efficient.
•HETP is given by Van Deemter equation,
HETP= A + B/u +Cu
A = Eddy diffusion term or multiple path
B = Molecular diffusion, depends on flow rate
C = Effect of mass transfer,depends on flow rate
u = Flow rate

24. Advantages of Gas Chromatography
•The technique has strong separation power and even complex
mixture can be resolved into constituents
•The sensitivity of the method is quite high
•It gives good precision and accuracy
•The analysis is completed in a short time
•The cost of instrument is relatively low and its life is generally long
•The technique is relatively suitable for routine analysis

25. Applications of Gas Chromatography
•G.C is capable of separating, detecting & partially characterizing the
organic compounds , particularly when present in small quantities.
• 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 subsequently identifying
these compounds by other method
•Quantitative Analysis - area under a single component elution peak
is proportional to the quantity of the detected component/response
factor of the detectors.
•Used for analysis of drugs & their metabolites.
•Checking the purity of a compound.

26. Applications of Gas Chromatography
•Miscellaneous-analysis of foods like carbohydrates, proteins, lipids,
vitamins, steroids, drug and pesticides residues, trace elements
•Pollutants like formaldehyde, carbon monoxide, benzen, DDT etc
•Dairy product analysis- rancidity
•Separation and identification of volatile materials, plastics, natural and
synthetic polymers, paints, and microbiological samples
•Inorganic compound analysis

27. Bibliography
1.Instrumental analysis by Skoog, Holler, and Crouch.
2.Instrumental methods of chemical analysis by B. K.
Sharma.
3.Pharmaceutical analysis by David G. Watson.
4.Principles of instrumental analysis by Douglas A. Skoog
and Donald M. West.
5.Basic gas chromatography by Harold M. McNair M.
Miller.