Gas chromatography

1. GAS CHROMATOGRAPHY
BY:- DEEPAK RAVI
ME student

2. CONTENTS
• CHROMATOGRAPHY
• DIFFERENT TECHNIQUES OF CHROMATOGRAPHY
• GAS CHROMATOGRAPHY
• REQUIREMENT FOR GAS CHROMATOGRAPHY
• BLOCK DIAGRAM OF GAS CHROMATOGRAPHY
• QUALITATIVE ANALYSIS
• ADVANTAGES AND DISADVANTAGES OF GAS
CHROMATOGRAPHY
• MODERN APPROACH

3. CHROMATOGRAPHY
Laboratory technique for the separation of a mixture.
The mixture is dissolved in a fluid called the mobile phase, which carries it
through a structure holding another material called the stationary phase.
 The various constituents of the mixture travel at different speeds, causing
them to separate.
 The separation is based on differential partitioning between the mobile and
stationary phases.
Chromatograph: equipment that enables a sophisticated separation, e.g.
gas chromatographic or liquid chromatographic separation.
Chromatogram: Visual output of the chromatograph.
 In the case of an optimal separation, different peaks or patterns on the
chromatogram correspond to different components of the separated mixture.

4. TECHNIQUES BASED ON
CHROMATOGRAPHIC BED SHAPE
Column chromatography: Separation technique in which the
stationary bed is within a tube.
Planar chromatography: Separation technique in which the
stationary phase is present as or on a plane.
The plane can be a paper, serving as such or impregnated by a
substance as the stationary bed (paper chromatography) or a layer of
solid particles spread on a support such as a glass plate (thin layer
chromatography)

5. TECHNIQUES BASED ON PHYSICAL STATE
OF MOBILE PHASE
Gas chromatography (GC): Also known as gas-liquid
chromatography, (GLC),
a separation technique in which the mobile phase is a gas. Gas
chromatographic separation is always carried out in a column, which
is typically "packed" or "capillary".
Liquid chromatography (LC): Separation technique in which the
mobile phase is a liquid.
carried out either in a column or a plane

6. GAS CHROMATOGRAPHY
Gas chromatography:
Mobile phase a carrier gas, usually an inert gas such as helium or
an nonreactive gas such as nitrogen.
Hydrogen is preferred for improved separations.
The stationary phase is a microscopic layer of liquid or polymer on an
inert solid support, inside a piece of glass or metal tubing called a column.
The instrument used to perform gas chromatography is called a gas
chromatograph.
The gaseous compounds being analysed interact with the walls of the
column, which is coated with a stationary phase. This causes each
compound to elute at a different time, known as the retention time of the
compound.
The comparison of retention times is what gives GC its analytical
usefulness.

7. CONTINUED….
The function of the stationary phase in the column is to separate different
components, causing each one to exit the column at a different
time(retention time).
As the carrier gas sweeps the analytic molecules through the column, this
motion is inhibited by the adsorption of the analytic molecules either onto
the column walls or onto packing materials in the column.
The rate at which the molecules progress along the column depends on the
strength of adsorption, which in turn depends on the type of molecule and
on the stationary phase materials.

8. CONTINUED……
Since each type of molecule has a different rate of progression, the
various components of the analytic mixture are separated as they
progress along the column and reach the end of the column at different
times(retention Time).
Detector: used to monitor the out let stream from the column; thus,
the time at which each component reaches the outlet and the amount of
that component can be determined.
Generally, substances are identified(qualitatively) by the order in
which they emerge(elute) from the column and by the retention time
of the analytic in the column.

9. REQUIREMENT FOR GAS
CHROMATOGHRAPHY
VOLATILITY:-Tendency of a substance to evaporate at normal
temperatures
POLARITY:-Substance comprised of molecules that contain unbalanced
localized charges (dipoles) is a polar substance.
 Polar substances tend to interact with other polar substances and rarely
react to a significant degree with nonpolar substances
When two atoms form a covalent bond, they each share an electron.
Different atoms have different abilities to attract electrons quantified by
their electronegativity values. When one atom in a covalent bond has a
much higher electronegativity than the other, the electron is found closer to
that atom than the weaker one. This creates a dipole effect with a slight
negative charge at the atom the electron favours and a slight positive charge
at the other

10. BLOCK DIAGRAM OF GAS
CHROMATOGRAPHY

11. COMPONENT OF GAS
CHROMATOGRAPH
carrier gas
flow regulator
injector
column
stationary phase
oven
detectors
display device

12. CARRIER GAS
• he(common),
• others:n2,h2
• safety; non-flammability, cost and efficiency are factors for gas
selection
• inertness
• suitable for the detector
• high purity
• easily available

13. FLOW METER
• Deliver the gas with uniform pressure/flowrate
• Flowmeters:-Rotameter

14. INJECTOR
• Transfers the sample into the column.
• Provides the means to introduce a sample into a continuous flow of
carrier gas.
• Injectors are usually heated to ensure sample’s transfer to a gas
phase.
• Volatile liquid or gaseous sample is injected through a septum.

15. COLUMN
Gas chromatography columns : packed and capillary.
Packed columns :A glass or stainless steel coil(typically1-5m total length and
5mm inner diameter), filled with the stationary phase, or a packing coated with
the stationary phase.
Capillary columns: A thin fused-silica (purified silicate glass) capillary
(typically10-100 m in length and 0.5 mm inner diameter) that has the stationary
phase coated on the inner surface.
Provides much higher separation efficiency than packed columns but are more
easily overloaded by too much sample.
The main chemical attribute regarded when choosing a column is the polarity of
the mixture, The polarity of the sample must closely match the polarity of the
column stationary phase to increase resolution and separation while reducing
runtime.

16. TEMPERATURE CONTROL DEVICES
Temperature Control Devices
Preheaters: convert sample into its vapour form, present along with
injecting devices
Thermostatically controlled oven
Temperature maintenance
in a column is highly essential
for efficient separation.

17. STATIONARY PHASES
For every polar sample, polyethylene glycol(thickess
0.25mircometer) is commonly used as the stationary phase.
Stationary Phases must have:
1.Low volatility
2.Thermal stability
3.Chemical inertness

18. SOME STATIONARY PHASE LIST

19. DETECTOR
Placed at the exit of the column.
Employed to detect and provide a quantitative measurement of the
various constituents of the sample
The choice of a particular type of detector is governed by the
following factors:
1. High sensitivity, sufficient enough to provide adequate signal for
even small sample
2. Response should be linear, unaffected by temperature and flowrate.
3. Non distorted shape of peak and non destructive.
4. Detector temperature must not condense the eluted vapours in it.
5. Simple & Inexpensive
6. Applicable to wide range of samples
7. Good reproducibility, rapidity and linearity.

20. COMMONLY USED DETECTOR
Most commonly used types:-
1.Thermal Conductivity Detector TCD
2.Flame Ionization Detector FID
3.Electron Capture Detector ECD
4.Atomic-Emission Detector AED
5.Flame Photometric GC Detector FPD

21. QUALITATIVE ANALYSIS
Chromatographic data is presented as a graph of detector response(y-axis)
against retention time(x-axis), which is called a chromatogram.
This provides a spectrum of peaks for a sample representing the analytics
present in a sample eluting from the column at different times.
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.

22. ADVANTAGES AND DISADVANTAGES
OF GC
ADVANTAGES:-
High Resolution
Very high sensitivity, detect down to 100 ppm.
Very good precision and accuracy.
Very good separation
Time(analysis is short), fast analysis is possible.
Small sample is needed-ml
Good detection system
Quantitatively analysis
DISADVANTAGES :-
Sample must be volatile
Dirty sample choke the capillary

23. MODERN APPROACH
GCMS:-Gas Chromatography Mass Spectrometry
Mass spectrometry: Analytical technique that ionizes chemical
species and sorts the ions based on their mass-to-charge ratio.
Gas chromatography–mass spectrometry (GC-
MS):Analytical method that combines the features of gas-
chromatography and mass spectrometry to identify different
substances within a test sample.
Applications of GC-MS include drug detection, fire investigation,
environmental analysis, explosives investigation, and identification of
unknown samples

24. GCMS:-GAS CHROMATOGRAPHY MASS
SPECTROMETRY

25. 2014 IEEE International Conference on Liquid Dielectrics, Bled Slovenia, June 30 -
July 3, 2014
Methanol Detection in Transformer Oils using Gas
Chromatography and Ion Trap Mass Spectrometer
S. Y. Matharagel, Q. Liul, E. Davenportl, G. Wilson2, D. Walker3 and Z.D.
Wang The University of Manchester, Manchester, M13 9PL, UK
2The National Grid Company, Warwick, CV34 6DA, UK
3Scottish Power, Blantyre, G72 OHT, UK

26. Continued…..
• Abstract-Paper ageing is an irreversible process, which has made
paper insulation a lifetime determining factor for transformers.
Chemical indicators in oil such as carbon oxide gases and 2-FAL, are
used to indicate the ageing state of paper as it is difficult to obtain
paper samples to measure DP or tensile strength. Methanol amount in
oil was recently found to be an early-ageing indicator for paper. In this
study, a heads pace gas chromatography mass spectrometry setup was
developed to measure methanol in transformer oil. This setup consists
of an auto sampler with a gas tight syringe, a gas chromatography unit
with 60 m VF-624ms column and a quadrupole ion trap type mass
spectrometer unit. Measurement of several laboratory-aged and
service-aged oil samples were conducted with both external standard
and internal standard calibration methods. Higher methanol values
obtained from internal standard method confirmed that it is more
suitable than external standard method.

27. REFERENCES
A text book of environmental chemistry by “BALRAM PANI”
“https://en.wikipedia.org/wiki/Gas_chromatography%E2%80%93mas
s_spectrometry
https://en.wikipedia.org/wiki/Gas_chromatography
https://www.youtube.com/watch?v=p3_WtEYIhTo
https://www.youtube.com/watch?v=gU2st5-T1Go