Gas chromatography is a technique used to separate and analyze mixtures that can be vaporized without decomposition. It works by partitioning components to be separated between a stationary phase and a mobile gas phase. The key components of a gas chromatography instrument are the carrier gas, injection port, column, temperature control system, and detector. Factors like temperature, flow rate, column length, and amount of sample injected can influence separation of the components. Gas chromatography has applications in qualitative and quantitative analysis and is used in quality control of pharmaceuticals.

1. GAS CHROMATOGRAPHY
Presented By
Rahul Krishnan.P.R
1st
Year M.Pharm
Dept. Of Pharmaceutics
Grace College Of Pharmacy, Palakkad

2. PRESENTATION OUTLINE
INTRODUCTION
PRINCIPLE
INSTRUMENTATION
CHROMATOGRAPHIC PARAMETERS
FACTORS AFFECTING RESOLUTION
APPLICATIONS

3. INTRODUCTION
Chromatography is the seperation of a mixture into individual
components using a stationery phase and mobile phase.
Based on nature of S.P and M.P, chromatography is divided into:
Gas-Solid Chromatography
Gas- Liquid chromatography
Solid-Liquid Chromatography (Column, TLC, HPLC)
Liquid-Liquid Chromatography (Paper Partition,Column
Partition)

4. Gas Chromatography-Principle
 GC consists of Gas-solid and Gas-Liquid Chromatography.
 Both types, Gas is used as stationery phase.
 In GSC, principle of separation is Adsorption.
 It is used rarely because of limited number of stationery
phases and increased resolution time.
Gas-Liquid Chromatography
 Principle of separation-Partition.
 Mobile Phase-Gas
 Stationery Phase-Liquid coated onto a solid support
 Components to be separated will be converted to vapour and
mixed with mobile phase.
 Component more soluble in stationery phase travels slower.
 Component less soluble in the stationery phase travels faster.
 No two components have same partition coefficient for fixed
combination of S.P,M.P and other conditions, hence

5. Separations
To detector
Time 1 Time 2 Time 3

6. INSTRUMENTATION
1. Carrier Gas
2. Flow regulators and flow Meters
3. Injection Devices
4. Columns
5. Temperature Control Devices
6. Detectors
7. Recorders And Integrators

8. 1. Carrier Gas
 Hydrogen-Good thermal conductivity, low density, inflamable
 Helium - Good thermal conductivity, but expensive
 Nitrogen - Inexpensive, Reduced sensitivity.
2. Flow Regulators and Flow Meters
 Rotameter
 Soap Bubble Meter

9. ROTAMETER
Placed before the column inlet.
It has glass tube with a float
held on spring.
Level of float is determined by
flow ratew of carrier gas

10. SOAP BUBBLE METER
Consist of soap solution in rubber
bulb.
Gas enters the meter
Bulb will be gently pressed
Drop of soap solution converted to
bubble by pressure of carrier gas
Distance travelled by the bubble
indicates flow rate.

11. INJECTION DEVICES
Direct injection is mostly used.
Types:
1.Automatic sampler
2.Headspace Sampling
3.Purge and Trap
4.Pyrolysis
Headspace sampling
Automatic sampler

13. Purge And Trap
Pyrolyser

14. COLUMNS
Most important part of the GC.
May be made up of Glass or stainless steel.
CLASSIFICATION

15. 5.TEMPERATURE CONTROL DEVICES
Two Operations are available:
1.Isothermal Programming- Same temp. throughout process
2. Linear Programming- Oven heateds linearly the peroid of
time

16. DETECTORS
1. THERMAL CONDUCTIVITY DETECTOR
2. FLAME IONISATION DETECTOR
3. THERMIONIC DETECTOR
4. ELECTRON CAPTURE DETECTOR

17. THERMAL CONDUCTIVITY DETECTOR
- based on electronic circuit known as a Wheatstone bridge.
- circuit consists of an arrangement of four resistors with a fixed current applied to them.
- thermal conductivity changes with presence of other components in the mobile phase.
- the voltage between points (+) and (-) will be zero as long as the resistances in the
different arms of the circuit are properly balanced
as solute emerge from column:
change in thermal conductivity  change in amount of heat removed from resistor 
change in resistor’s temperature and resistance  change in voltage difference between
points (+) and (-).
-one resistor in contact with mobile
phase leaving column
-another in contact with reference
stream of pure mobile phase

18. 2.) Flame Ionization Detector (FID)
- most common type of GC detector
- “universal” detector capable of measuring the presence of almost any organic and many
inorganic compound
Process
- measures the production of ions when
a solute is burned in a flame.
- ions are collected at an electrode to
create a current

19. 3.)THERMIONIC DETECTOR
- used for detecting nitrogen- or phosphorus containing compounds
- also known as alkali flame ionization detector or thermionic detector
Process
- same basic principal as FID
- measures production of ions when a solute
is burned in a flame
- ions are collected at an electrode to
create a current
- contains a small amount of alkali metal
vapor in the flame
- enhances the formation of ions from
nitrogen- and phosphorus- containing compounds
Alkali Bead

20. 4.) Electron Capture Detector (ECD)
- radiation-based detector
- selective for compounds containing electronegative atoms, such as halogens
Process
- based on the capture of electrons by
electronegative atoms in a molecule
- electrons are produced by ionization of the
carrier gas with a radioactive source
‚ 3
H or 63
Ni
- in absence of solute, steady stream of
these electrons is produced
- electrons go to collector electrode where
they produce a current
- compounds with electronegative atoms
capture electrons, reducing current

21. PARAMETERS USED IN GAS
CHROMATOGRAPHY
1.RETENTION TIME
The difference in the time between the point of injection and the
appearance of the peak maxima.
It is the time required for 50% of the compound to be eluted from a
column.
Measured in minutes or seconds

22. RETENTION VOLUME
The volume of the career gas required to elute 50% of the component from the
column.
Retention volume= Retention time X Flow rate
SEPERATION FACTOR
Ratio of the partition coefficients of the two components to be separated.

23. RESOLUTION
It is the measure of the extent of separation of two components and the baseline
seperation achieved.
It is determined by following formula:

24. PLATE THEORY
Hypothetical theory.
View column as divided into a number (N) of adjacent imaginary segments
called theoretical plates
Within each theoretical plate analyte(s) completely equilibrate between
stationary phase and mobile phase Theoretical plate
The No. of theoretical plates can be determined by following equation:
n = 16 (Rt/w)2
n= no: of theoretical plates
Rt= Retention time
W= Peak width

25. Chromatographic principle
The molecules of the
mixture interact with the
molecules of the
Mobile and Stationary
Phase
Retardation of rate
of movement of
molecules
Each molecule
interacts differently
with MP and SP
Different distribution
coefficients and different
net rates of migration
Stationary phase
Mobile phase
Sample
mixture
Equilibrium
establishes at each
point (ideally)

26. HEIGHT EQUALENT TO THEORATICAL PLATES
Plate theory did not suggest the ways of improving perfomance of the column.
Hence, rate theory came and is widely used now.
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
HETP (length of the column)
(No of theoritical 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

27. ASSYMMETRY FACTOR
Chromatographic peak should be symmetrical about its centre
If peak is not symmetrical- shows Fronting or Tailing
FRONTING
Due to saturation of S.P & can be avoided by using less quantity of
sample
TAILING
Due to more active adsorption sites & can be eliminated by support
pretreatment

28. FACTORS INFLUENZING THE
SEPERATION
1. Vapour Pressure
 The lower the boiling point is, the higher the vapor pressure of the
compound and the shorter retention time usually is because the compound will
spent more time in the gas phase
2. Polarity
 If the polarity of the stationary phase and compound are similar, the
retention time increases because the compound interacts stronger with the
stationary phase. As a result, polar compounds have long retention times on
polar stationary phases and shorter retention times on non-polar columns using
the same temperature.
3.Column Temperature
 As temperature increases, retention time decreases, but the seperation will
be very poor because most of the compoud stay in the gaseous phase itself.
 The best separations are usually observed for temperature gradients,
because the differences in polarity and in boiling points are used here.

29. 4.Carrier Gas Flow Rate
A high flow rate reduces retention times, but a poor
separation would be observed as well.
5. Column Length
A longer column generally improves the separation. The
trade-off is that the retention time increases proportionally to
the column length and a significant peak broadening will be
observed.
6. Amount of Material Injected
If too much of the sample is injected, the peaks show a
significant tailing, which causes a poorer separation.

30. APPLICATIONS
1.QUALITATIVE ANALYSIS
 When 2 substance gives coincident peak (one known and one unknown), it is
evidence that the compounds may same.
Retention characterstics of unknown compound determined by:
a)Specific Retention volume (Vg) – Flow rate of carrier gas X Adjusted Retention
time)
 But in this, reproducibility is very low due to varying packing density,liquid
loading, activity of support, age etc.
a)Relative retention (rA / B
) – Adjusted retention volume of substance A related to
that of reference standard B.
Here reproducibility is good

31. QUANTITATIVE ANALYSIS
Size of the chromatographic peak is propotional to amount of the compound.
By measuring accurately the peak area or hight, quantitative analysis can be done.
Peak Area Determination
1.Mechanical or Electronic integration
2.Triangulation
3.Planimetry
4.Cut and Weigh method
Peak Height determination
1.Recorders and integrators
2.Measuring with ruler
Data Interpretation
1.External standardization
2.Internal standardization

32. 3. Presence of impurites.
4.Used in the quality control of :
Antibiotics - Pencillin, Gentamycin
Anti T.B drugs - Isoniazid, Ethambutol
Antivirals - Amantadine, Idoxuridine
Anti neoplastics - Flurouracil, Doxorubin

33. REFERENCES
1.Pharmaceutical analysis Modern Methods by James W. Munson,
Page no: 15-76
2.Instrumental method of analysis by Willard, Page No: 540-560
3.Pharmaceutical Analysis Volume II Instrumental methods by Dr.
A.V Kasture, Page No:58-75
4.Textbook of Pharmaceutical Analysis by Dr. S. Ravishanker, Page
No: 17.1-17.20