Gas chromatography is the separation of gaseous and volatile substances which is achieved by employing gas as a mobile phase and moving it through a column containing stationary phase which could be a liquid or solid. Two methods of temperature control are used during gas chromatography: Isothermal operation and; Temperature programming

1. PRINCIPLE AND APPLICATION OF
PTGC AND ISOTHERMAL
PROGRAMMING
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Presented by- Athira K
1st M pharm
Dept of industrial pharmacy
Srinivas college of pharmacy

2. CONTENTS
• Introduction
• Isothermal programming
 Principle
 Drawback
• Programmed temperature gas chromatography
 Principle
 Drawback
 Application
• Reference
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3. INTRODUCTION
• Gas chromatography is the separation of gaseous and volatile
substances which is achieved by employing gas as a mobile phase and
moving it through a column containing stationary phase which could be
a liquid or solid.
• The mobile phase is an inert gas such ass argon, helium or hydrogen.
• The liquid stationary phase coats the inner side of the column as a thin layer
in the gas chromatography.
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4. • Temperature play a crucial role in GC seperations. The Gas
Chromatographic column can be either be maintained at uniform
temperature during the analysis or its temperature can be varied at
predetermined rate.
• Higher temperature- faster speed of analysis but less resolution
• Lower temperature- slower analysis but better resolution
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5. Two methods of temperature control are used
during gas chromatography:
• Isothermal operation and;
• Temperature programming
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6. ISOTHERMAL PROGRAMMING
• During isothermal programming, the column runs at a constant temperature
throughout the process.
• The temperature at the mid point of the boiling range is used as the isothermal
temperature.
• Isothermal temperature conditions are used for solutes with similar retention.
• Retention differences for dissimilar solutes can be severe for isothermal
conditions.
• Peak width rapidly increases with retention for isotheral conditions.
• If a sample contains components with closely similar boiling point, adequate
separation with a short analysis time is obtained at one specific oven
temperature. This is called an isothermal analysis
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7. DRAWBACKS OF ISOTHERMAL PROGRAMMING
There are disadvantages in this method when the sample contains heavy
compounds with higher molecular mass and higher boiling points.
These disadvantages include
• Poor resolution of lighter components at higher temperature.
• Broad peaks for the components that elute later.
• Carry over effect of heavier components due to decomposition.
• Longer run times.
• Lower sample throughput
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8. • The mode is satisfactory for resolving peaks of low boiling point
components of the sample.
• The temperature is set to around midpoint of boiling point range of the
sample components. If the temperature is set at too high value the
lighter components will co-elute resulting in poor resolution.
• The higher boiling range components elute eventually due to the
higher retention times but undesirable band broadening occurs.
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9. PROGRAMMED TEMPERATURE GAS
CHROMATOGRAPHY
• A technique in which column temperature is increased either
continuously or in steps as the separation proceeds.
• In general, optimum resolution is associated with minimal
temperature.
• Lower temperature results in longer elution times and hence slower
analysis.
• Using temperature programming, low boiling point constituents are
separated initially t temperature that provide resolution..
• As separation proceeds, column temperature is increased so that the
higher boiling point constituents come off the column with good
resolution and at reasonable length of times.
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10. • The ramp rate or the elution rate is proportional to the column
temperature.
• In the beginning, it uses lower temperature that gives a higher
resolution of lighter compounds.
• With the increasing temperature, the ramp rate of heavier compounds
also increases.
• This gives sharper peaks for heavier compounds. 10

11. Temperature programmed mode referes to a continual rise of temperature at
predetermined rate during the sample analysis. This mode of operation
offers several advantages such as
• Improvement of peak shapes
• Improvement of resolution
• Completion of analysis in a fraction of time it would take for the
isothermal operation
The above mentioned advantages are clearly seen in the representative
chromatograms of hydrocarbons C6 to C21 having boiling ranges from
70°C to 360°C in the two modes
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Fig; isothermal chromatogram
Fig; temperature gradient
chromatogram

13. DRAWBACKS OF TEMPERATURE PROGRAMMING
• The temperature of injector and detector needs to be maintained at
constant value in separate heat zones which are independent of oven
temperature. This requires special design features to be incorporated
into the instrument.
• Column bleed. Ie; loss of vapour of the liquid coating of stationary
phase can occur over the temperature range of the programme.
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14. APPLICATION
• Resolution of low boiling point solutes can be maintained.
Eg. Diethyl ether, dichloromethane
• Retention time of high boiling solutes decreases
Eg. Carbon disulphide and sulphur dioxide
• Microcoulometric detection of chlorinated insecticide.
• Distinguish OW-9 residues(mixture of 2 organosulfites closely related
to the structure of aramite) from aramite residues on citrus fruits
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15. REFERENCE
1. J. Mendham, R.C Denney ,Vogels textbook of quantitative chemical
analysis; 6th edition page no 651.
2. Dr. S Ravisankar, Textbook og pharmaceutical analysis, 4th edition
page no 402
3. Dr A V Kasture, Dr K R Mahadik, Dr S G Wadokar, Dr H N More,
pharmaceutical analysis Vol 1, pg no 321
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