Principle and application of ptgc and isothermal programming

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 1 Presented by- Athira K 1 st M pharm Dept of industrial pharmacy Srinivas college of pharmacy

2. CONTENTS Introduction Isothermal programming P rinciple D rawback Programmed temperature gas chromatography Principle Drawback Application Reference 2

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. 3

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 4

5. Two methods of temperature control are used during gas chromatography: Isothermal operation and; Temperature programming 5

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 6

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 7

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 . 8

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. 9

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 11

12. 12 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 . 13

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 14

15. REFERENCE 1. J. M endham, R.C Denney , Vogels textbook of quantitative chemical analysis; 6 th edition page no 651. 2. Dr. S Ravisankar , Textbook og pharmaceutical analysis, 4 th 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 15

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