gas chromatography

1. Gas
Chromatograp
hy
Prepared by
Amit Shrestha
1st M.pharm(pharmacology)
Mallige college of pharmac
05-06-2013

2. History
Introduction
Principle
Theory
Instrumentation
Carrier gas
Flow regulator
 Flow meter
 Injection device
 Columns
 Temperature control device
Detector
Application

3. Mikhail Tswett invented
chromatography in 1901
during his research on
plant pigments.
He used the technique to
separate various plant
pigments such as
chlorophylls, xanthophylls
and carotenoids.
Invention of Chromatography
Mikhail Tswett
Russian Botanist
(1872-1919)

4. Introduction
It is an analytical technique used for separation
Of thermal stable and volatile substances.
Mobile phase Gas
Stationary phase  Solid (or) Liquid
I
Qualitative technique:
Can be used to identify compounds if
standards are used
Quantitative technique:
Can be used to determine relative
amounts of compounds present in a
mixture

5. Principles
Adsorption (or)
partition
Depending on the
Stationary phase used
If Stationary phase is
liquid Gas Liquid Chromatography Partition
Solid  GAS Solid Chromatography  Adsorption
Principle
involved
•In general, compounds with low
boiling points (and high vapor
pressures) spend more time in the
mobile phase and elute from the
column in a shorter amount of time
than compounds with high boiling
points

6. Theory
The component to be separated
from Gas Chromatography
Should be Volatile & Thermostability

7. Instrumentation
Carrier gas
Flow regulator
 Flow meter
 Injection device
 Columns
 Temperature control
device
Detector

8. Schematic of a Commercial Gas Chromatograph

9. HP 5890 Capillary Gas Chromatograph
with Robotic Sample Injector and Data Station

10. carrier gas
the mobile phase (or “ moving phase")
is a carrier gas, usually an inert gas
such as helium or an unreactive gas
such as nitrogen
NOTE: Probably more than 90% of the present
GC instruments run with helium as carrier gas.
Some people use hydrogen or nitrogen
H  Adv: better thermal conductivity , low density
disadv: it reacts with unsaturated compound
& it is inflammable.
He  adv: excellent thermal conductivity
disadv: expensive
N adv: inexpensive
disadv: reduced sensitivity

11. Flow Regulator
As carrier gases are stored under high
Pressure, Flow regulator are used to deliver the
Gas with uniform pressure or flow rate
Flow meter
Rotameter
it is placed conveniently before the column inlet. It has an ordinary
glass tube (like burette) with a float held on to spring, the level of
the float is determined by the flow rate of carrier gas and is precalibrated

12. Column
made of glass or metal such as stainless steel
stainless steel  long life.
handled easily but react with some compound
Glass widely used as they are inert but highly fragile
Column can be used both for preparative and analytic purpose
Types
Packed column:
GSC:-packed with graded adsorbent or porous polymers
GLC:- “ “ liquid phase coated graded inert solid support
Open tubular column:
also called capillary or Golay column
made up stainless steel with long capillary tubing in length and have
uniform and narrow internal diameter
Support coated open tubular column
improve version of OTC

13. Stationary phase:
GSC non volatile liquid
Ex: PEG, Amides., Hydrocarbons, Carbowax etc
GLC  interactive solids such as molecular sieves or porous polymers
Ex: Na & Ca analogue of potassium aluminosilicate,
polymer made of acrylic esters

14. Sample injection system:
Injected by Hypodermic Syringe from rubber
septum
A hypodermic needle is used for rapid
delivery of liquids

15. DETECTORS:
Flame ionization detector
amplifier
Hydrogen
Air or o2
Collector Electrode
Polarising electrode
Operating principle
The operation of the FID is based on the detection of ions formed
during combustion of organic compounds in a hydrogen flame.
The generation of these ions is proportional to the concentration of
organic species in the sample gas stream.
flame
Carrier gas from column
Operation:
• At normal temperature and pressure gases acts as
insulator but become conductive if ions are present.
• it is also based upon electrical conductivity of carrier
gases.
• when pure gas is passes alone there is no ionization and
no current flow.
• when component is emerge from column no. of ions are
produced becoz of ionization by the thermal energy of
the flame. This cause potential difference & cause a
flow of current which is amplified & recorded
Platinum capillary at the tip  cathode
Silver gauge above  anode
FID stable and sensitive to small change in flow rate

16. Advantages
relatively inexpensive to acquire and operate
Low maintenance requirement
FIDs are relatively resistant to misuse.
Linearity and detection ranges: FIDs can measure organic
substance concentration at very low and very high levels
Disadvantages
cannot differentiate between different organic substances
They also cannot detect inorganic substances

17. Thermal conductivity detector
also known as a Katharometer, is a bulk property detector and a chemical
specific detector commonly used in gas chromatography
This detector senses changes in the thermal
conductivity of the column effluent and compares it to
a reference flow of carrier gas

18. •Principle  thermal conductivity difference between carrier gas
and that of component.
•It consists two platinum wires of uniform dimension which form
part of wheat stone bridge.
1st wire  carrier gas flow
2nd wire  effluents of the column passes
•2 platinum wire is heated electrically for equilibrium condition
of temperature and electrical resistance
•When sample passes through column it alerts thermal
conductivity & resistance of the wire & the difference in
thermal conductivity is amplified and recorded as a signal.
TCD SchematicTCD Schematic
H & He higher thermal conductivity

19. Advantages
the device is inexpensive and has good accuracy
The TCD is often called a universal detector because it
responds to all compounds
the TCD is less sensitive than the
flame ionization detector

20. Overview
 When each component reaches the detector
(OCCC’s instrument uses a TCD), the
filament in the detector heats up, ultimately
resulting in an electrical signal that is
digitized and sent to the attached computer.
 A chromatogram is generated.
◦ A graph of the intensity of
the detector’s response as
a function of time

21. Determining Identity
 The number of components present in
a mixture is indicated by the number of
peaks observed.
 Under a very specific set of conditions,
the retention time for a compound can
be used to help identify a compound.
◦ The amount of time from injection
for a sample to reach the detector
Retention time:
it is the difference in time between the
point of injection & appearance of peak maxima
•Retention time varies with changes in
the identity of a compound and with
experimental conditions including:
•type and amount of stationary
•Phase
•length of column,
•gas flow rate,
•temperature profile

22. Application
Let us check it out some of the applications of gas chromatography. It has many uses as well as applications and
advantages which are useful for the separation of a given unknown mixture. It is a physical method to separate this
mixture. Gas Chromatography have many advantages compared to other separation analysis methods.
Some of the different applications of gas chromatography where it can be used such as:
Used in pharmaceuticals
used in pollutants
petroleum
petrochemicals
oils
fats
food and flavors
vitamins
steroids and alkaloids
blood and serum
pesticides and fungicides
radioactive isotopes
used in cosmetics
used in environmental toxins.
These are some of the fields where GC can be used for the separation of volatile mixtures.
It can also be used for the volatile samples such as human breathe, blood, saliva and other secretions which
contains organic volatiles and can be easily analyzed with Gas Chromatography.
This GC is very much useful in studying of health of human as well as environment. Again gas chromatography
have many advantages.
Air samples can also be analyzed with GC.
Air quality control units also use Gas Chromatography in order to determine the components of a given air sample.
Manufacturers of Cosmetics also use gas chromatography to effectively measure how much of each chemical is
used for their products.

23. •In general, substances that vaporize
below ca. 300 °C (and therefore are
stable up to that temperature) can be
measured quantitatively
•Very minute amounts of a substance
can be measured