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GAS CHROMATOGRAPHY
Applications of Gas Chromatography
• Separation and analysis of volatile organic
compounds
• Testing purity of compounds
• Determine relative amounts of components in
mixture
• Compound identification
• Isolation of pure compounds (microscale work)
• Examples include various hydrocarbons, Fatty
acids, esters, aldehydes, alcohols, essential oil,
Perfumes, Pesticides, insecticides etc
...
Parts of Gas Chromatograph
Microliter Syringe
Heated injection port with rubber septum for
inserting sample
Heating chamber with carrier gas injection port
Oven containing copper, stainless steel, or glass
column
...
WCOT columns are examples of capillary
columns which are most frequently used
...
• Polyethylene glycol (trade name Carbowax) is
an example of non polar GC column which is
used to separate aldehydes, ketones, Fatty
acid methyl esters etc
...
Sample injected with microliter syringe into the
injection port where it is vaporized and mixed into
the Carrier Gas stream (helium, nitrogen, argon)
...
The time the different compounds in the sample
spend in the Vapor Phase is a function of their
Vapor Pressure
...
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Principals of Detection
Famous Detector Types
Thermal Conductivity Detector (TCD)
Flame Ionization Detector (FID)
Electron Capture detector (ECD)
TCD is electrically heated “Hot Wire” placed in
carrier gas stream
Thermal conductivity of carrier gas is higher than
most organic substances
...
Two detectors used: one exposed to sample gas
and the other exposed to reference flow of carrier
gas
...
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• FID is used for the detection of fatty acid
methy esters
...
• ECD is used for the detection of pesticides and
insecticides
...
Factors Affecting Separation in GC analysis
Boiling Points of Components in Sample
Low boiling point compounds have higher
vapor pressures
...
e
...
Boiling point increases as molecular weight
increases
...
Length of Column
Similar compounds require longer columns
than dissimilar compounds