Gas chromatography is an analytical technique used to separate and analyze chemical compounds. It involves vaporizing a sample and injecting it into a column with a gaseous mobile phase. Components are separated based on how they partition between the mobile and stationary phases. The separated components exit the column and are detected, producing a chromatogram. Key advantages are its speed, sensitivity, and ability to analyze volatile organic and inorganic compounds. Common detectors include the flame ionization detector and thermal conductivity detector. Gas chromatography has many applications in fields like drug analysis, food testing, and environmental analysis.

1. INTRODUCTION OF GAS
CHROMATOGRAPHY
PREPARED BY, MISS.RAJESHREE
SUBHASH PATIL.
Guided By,
Dr. Rajesh J Oswal
Prof. Sandip Kshirsgar
DEPARTMENT OF PHARMACEUTICAL
CHEMISTRY
JSPM’s
Charak College of Pharmacy and Research,
Gat No. 720/1 &2, Wagholi, Pune-Nagar
Road, Pune-412 207

2. CONTENT
 INTRODUCTION
 ADVANTAGES OF GC
 DISADVANTAGES OF GC
 TYPE OF GC
 COLUMNS OF GC:- packed column
open(capillary) column
o COLUMN SELECTION PARAMETERS
o GC BLOCK DIAGRAM
o SAMPLE FOR GC
o INSTRUMENTATION
o DETECTORS
o CHROMATOGRAPHIC ANALYSIS
o LIMITATION OF GC
o APPLICATION OF GC

3. INTRODUCTION
Gas chromatography is an instrumental method for the separation and
identification of chemical compounds.
• GC is most widely used analytical technique in the world.
-Over 50 years in development
-2,000 instrument / yr
-25,000 in use
-Worldwise market > $ 1 billion
• GC is premier technique for separation and analysis of volatile compounds.
-gases, liquids, dissolved solids.
-Organic and inorganic materials
-MW from 2 to > 1,000 Dalton
Gas chromatography - specifically gas-liquid chromatography - involves a
sample being vaporized and injected onto the head of the chromatographic
column. The sample is transported through the column by the flow of inert,
gaseous mobile phase. The column itself contains a liquid stationary phase
which is adsorbed onto the surface of an inert solid.

4. Have a look at this schematic diagram of a gas chromatograph:

5. ADVANTAGES OF GC
Fast analysis
-Typically minutes (even sec.)
-Can be automated
 Small samples (µl or µg needed)
High resolution
 Reliable, relatively simple and cheap(~$ 20,000)
 Non-destructive
-Allows on-line coupling e.g. to MS
 Sensitive detectors(easy ppm , often ppb)
• Highly accurate quantification(1.5% RSD)
•

6. DISADVANTAGES OF GC
 Limited to volatile samples
-T of column limited to~ 380°c
-Need Pvap of analyte ~60 torr at that T
 Not suitable for thermally labile samples
 some samples may required intensive preparation
-Samples must be soluble and not react with the column
• Requires spectroscopy(usually MS) to confirm the peak identity.
•TYPES OF GC:-
GLC- gas liquid chromatography
Stationary phase:- solid
Principle is ADSORPTION
GSC- gas solid chromatography:
Stationary phase:- immobilized liquid
Principle is PARTITION

7. Columns can be short, large diameter
packed column or long, very small
diameter capillary columns.
Each has its own use and associated
advantages and disadvantages

8. columns

10. PACKED GC COLUMN
#Easy to make and use
#Limited resolution(N<8,000)
#Outside: solid tubing usually made of stainless steel
-because of strength
-glass when more inert substrate is needed
# Inside : tightly packed with inert support
-solid supports should be inert and have high surface area.
- typically diatomaceous earth or fluorocarbon polymer
#Stationary liquid phase is coated on the solid support
- 3-10% by weight of the solid support

11. OPEN (CAPILLARY) COLUMN
# Most common & efficient
# High resolution (N>100,000)
#Outside :solid tubing made from fused silica
-inert , flexible, strong & easy to use
# Inside :column is an open tube
-very low resistance to flow
-long length possible(L>100m)
#Stationary phase is a thin, uniform liquid film coated on the wall of the
tubing.

12. COLUMN SELECTION PARAMETERS
# The critical parameters for GC column :
-dimensions :internal diameter ,column length , film thickness
-conditions : temperature , flow rate
-composition –stationary phase composition, carrier gas
#Given a sample, you will need to first choose the what stationary phase will
work best
-first pick the type of column ,then think about dimensions
-conditions can be optimized for given column dimension
#Choice of stationary phase is very important
-it determines what kind of sample you can run
-critical for packed columns ,but less so for OT columns
because of high efficiency

14. The injector, column oven and detector
components of the Varian 3350 gas
chromatograph are shown below.
Detector
Injector
Column in Oven

15. 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
SAMPLE FOR GC
Gases, liquids or solids
Molecular weight 2 to ~800
Organic or inorganic
 Samples must be volatile

16. INSTRUMENTATION
Theory
A gas chromatograph consists of a flowing mobile phase, an
injection port, a separation column containing the stationary
phase, a detector, and a data recording system. The organic
compounds are separated due to differences in their partitioning
behavior between the mobile gas phase and the stationary phase in
the column.
Mobile Phase (Carrier gas)
The carrier gas must be chemically inert. Commonly used gases
include nitrogen, helium, argon, and carbon dioxide. The choice of
carrier gas is often dependant upon the type of detector which is
used. The carrier gas system also contains a molecular sieve to
remove water an

17. CARRIER GAS
**Hydrogen :- better thermal conductivity
advantage:- It reacts with unsaturated compounds &
inflammable.
** Helium :- excellent thermal conductivity
It is expensive
** Nitrogen :- reduced sensitivity
It is inexpensive.
FLOW REGULATORS & FLOW METERS
** deliver the gas with uniform pressure / flow rate.
** Flow Meters :- Rota meter & Soap bubble flow meter

18. Stationary Phase
The most common stationary phases in gas-chromatography columns
are polysiloxanes , which contain various substituent groups to change
the polarity of the phase. The nonpolar end of the spectrum is
polydimethyl siloxane , which can be made more polar by increasing the
percentage of phenyl groups on the polymer. For very polar analytes ,
polyethylene glycol (a.k.a. carbowax ) is commonly used as the
stationary phase. After the polymer coats the column wall or packing
material, it is often cross-linked to increase the thermal stability of the
stationary phase and prevent it from gradually bleeding out of the
column.
Small gaseous species can be separated by gas-solid chromatography.
Gas-solid chromatography uses packed columns containing high-
surface-area inorganic or polymer packing. The gaseous species are
separated by their size, and retention due to adsorption on the packing
material.

19. INJECTIONPORT
The sample to be analyzed is loaded at the injection port via a
hypodermic syringe . The injection port is heated in order to
volatilize the sample . Once in the gas phase, the sample is
carried onto the column by the carrier gas, typically helium .
The carrier gas is also called the mobile phase. Gas
chromatographs are very sensitive instruments .Typically
samples of one micro liter or less are injected on the column .
These volumes can be further reduced by using what is called
a split injection system in which a controlled fraction of the
injected sample is carried away by a gas stream before
entering the column.

20. DETECTORS
 Heart of the apparatus
The requirements of an ideal detector are-
*Applicability to wide range of samples
*Rapidity
*High sensitivity
*Linearity
*Response should be unaffected by temperature, flow rate…
*Non destructive
*Simple & inexpensive.

21. DIFFERENT DETECTORS
•discharge ionization detector (DID), which uses a high-voltage electric
discharge to produce ions.
•dry electrolytic conductivity detector (DELCD), which uses an air phase
and high temperature (v. Coulsen ) to measure chlorinated compounds.
•electron capture detector (ECD), which uses a radioactive Beta particle
(electron) source to measure the degree of electron capture.
•flame photometric detector (FPD)
•flame ionization detector (FID)
•Hall electrolytic conductivity detector (EICD)
•helium ionization detector (HID)
•Nitrogen Phosphorus Detector (NPD)
•Infrared Detector (IRD)
•mass selective detector (MSD)
•photo-ionization detector (PID)
•pulsed discharge ionization detector (PDD)
•thermal energy(conductivity) analyzer/detector (TEA/TCD)
•thermionic ionization detector (TID)

22. Flame Ionization Detector
(FID)
• Column effluent is passed
through a H2-Air flame
– Produces ions and electrons
• Charged particles are
accelerated by voltage applied
between jet and collector
– results in current (pA)
• Number of ions depends on
number of reduced (methylene)
carbons in molecule
– one molecule of ethane gives
twice the signal of one molecule of
methane
– less sensitive for non-hydrocarbon
groups
– insensitive to H2O, CO2, SO2 and
other noncombustibles
• High sensitivity, good LDR (107) , low
noise, destructive

23. Thermal Conductivity Detector
(TCD):
• Element is electrically heated at constant
power
– Temperature depends on thermal
conductivity of
surrounding gas
• Measure conductivity (resistance) with
respect
to a “reference”
• Hydrogen and helium carrier gas provide
best sensitivity
– most thermally conductive
– Organics are less so
– when analyte comes off, filament
temperature goes up, resistance goes down
• Poorer sensitivity than FID, but more
universal
• Large LDR (105), non-destructive

24. Electron Capture
Detector (ECD):
• Carrier gas (and analyte) passes
over β-emitter, resulting in
ionization and e- production
• Produces current between
electrodes
• In the presence of other
compounds
(especially halogens, etc.) electrons
are
captured, causing decrease in
current
• Most commonly used for
halogenated organics (insecticides,
etc.), small LDR (102)

25. 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.
 LIMITATION OF GC
 Sample must be volatile
 Dirty sample require clan up
 Must use another instrument(eg.MS) for confirmation of identity
 some training /experience necessary

26. APPLICATION OF GC
 GC is capable of separating, detecting & partially characterizing the
organic compounds, particularly when present in small quantities.
# Qualitative analysis :- Rt & Rv are used for the identification &
separation.
# Checking the purity of a compound :- compare the chromatogram of
the std. & that of the sample.
#Quantitative analysis :- It is necessary to measure the peak area or
peak height of each component.
# Used for analysis of drugs & their metabolites.
# Semi quantitative analysis of fatty acids.
# Tentative identification of unknown compounds.

27. Quantitative and Qualitative Analysis
• Qual.: Retention Index (Kovats Number)
– Regardless of column, separation conditions, etc.,
define the retention index (RI)
of a normal alkane as 100n, where n = # of aliphatic
carbons
RI = 100n
– RI for all other compounds will
vary, depending on experimental
conditions, but RI for n-alkanes
is fixed.
– RI is related to retention time!
– Useful for comparing multiple
components in a separation
• Quant:
– To a large degree, sensitivity is controlled by the
detector, while selectivity is
controlled by the separation conditions
– Both need to work well to provide good accuracy and
precision!

28. Two-dimensional GC
• Coupled GC columns
– “Heart-cut” or
“Comprehensive”
• Leads to improved
qualitative (ID) information

29. THANK YOU