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
CONTENT
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INTRODUCTION
ADVANTAGES OF GC
DISADVANTAGES OF GC
TYPE OF GC
COLUMNS OF GC:- packed column
open(capillary) column
COLUMN SELECTION PARAMETERS
GC BLOCK DIAGRAM
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SAMPLE FOR GC
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INSTRUMENTATION
DETECTORS
CHROMATOGRAPHIC ANALYSIS
LIMITATION OF GC
APPLICATION OF GC
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
-2,000
50 years in development
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
-MW
Gas
and inorganic materials
from 2 to > 1,000 Dalton
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.
Have a look at this schematic diagram of a gas chromatograph:
ADVANTAGES OF GC
Fast
analysis
-Typically
-Can

minutes (even sec.)
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)
•
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
GLC-
OF GC:-
gas liquid chromatography
Stationary phase:- solid
Principle is ADSORPTION
GSC-
gas solid chromatography:
Stationary phase:- immobilized liquid
Principle is PARTITION
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
columns
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
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.
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
The injector, column oven and detector
components of the Varian 3350 gas
chromatograph are shown below.
Injector
Detector
Column in Oven
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
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
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
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 highsurface-area inorganic or polymer packing. The gaseous species are
separated by their size, and retention due to adsorption on the
packing material.
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.
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.
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)
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
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
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)
CHROMATOGRAPHIC ANALYSIS
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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.
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LIMITATION OF GC

Sample must be volatile
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Dirty sample require clan up
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Must use another instrument(eg.MS) for confirmation of identity
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some training /experience necessary
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.
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!
Two-dimensional GC
• Coupled GC columns
– “Heart-cut” or
“Comprehensive”
• Leads to improved
qualitative (ID) information
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