GAS CHROMATOGRAPHY:

•       It is Similar to HPLC (High Phase Liquid Chromatography)

•     Mobile phase is gaseous in nature.

•     Stationary phase is a liquid coated on the inert solid.

•     Samples are vapourized , introduced into the warm gaseous phase and swept through the stationary phase.

INSTRUMENTATION:

   Consists of five basic components:

1.  Injector

2.  Column

3.  Mobile phase

4.  Detector

5.  Recorder

COMPONENTS:

INJECTOR:

•       May use manual or automated injection

•      The sample is injected through a heated rubber septum

•      It is made volatile by the use of flash heater and is swept through the column by a carrier gas

•      Temperature of injector and detector is 10degree more than the column

COLUMN:

•       Can be a packed column or a capillary column , enclosed in a oven

•      The oven provides an uniform temperature into the column.

•      A fan may kept to enhance the temperature regulation.

•      The temperature is maintained uniformly to avoid condensation of some samples.

 

 

PHASES
Stationary phase	Mobile phase
•     A high boiling point liquid material such as Silicon grease or wax that is either coated onto the internal wall of the column or supported on an inert granular solid and packed into the column. •     Commonly used solid supporters are diatomaceous earth,teflon powder,glass beads.	•     A gas cylinder filled with a carrier gas of high purity(carrier gas) •     The most commonly used gases are Helium, Nitrogen, Hydrogen, Argon. •     Equipped with meters so as to control the flow of the gas and thus control the ultimate gas pressure through the column.

 

    DETECTOR:

       Commonly used detectors in gas chromatography include

1.    Thermal conductivity detector   

2.       flame Ionization detector

    3.  Electron capture detector

      

Flame Ionization detector:

•      Identifies compounds by measuring their ability to produce various ions when burned in a hydrogen flame

•      The ions produced are gathered by the electrode which surrounds the flame

•      The detector response is proportional to the amount of organic material in the carrier gas.

                             

 RECORDER:

•     Functions to process, record and store the information collected by the detector.
•      Recording system outputs may range from simple graphical representation to sophisticated computer analysis of the data.
•       The type of detector used and the type of sample being measured plays a significant role in the choice of recording systems.

 

 WORKING:

•                                  The vaporized sample is carried to the column partially as a gas and partially as a dissolved substance in a liquid phase.

•                                 The more volatile the compound the quicker it moves into the column, less volatile will spend more time in the stationary phase.

•                              The degree of volatility depends on the boiling point of the compound.

•                                  The partition coefficients are inversely proportional to the volatility of the analytes.

 

ADVANTAGES	DISADVANTAGES
•      High resolution power compared to other methods •      High sensitivity, accuracy, precision •      Analysis of sample very quickly •      Provides excellent separation of most small biomolecules	•      It is limited to separating compounds that can be converted to a volatile derivative. •      Requires mass spectroscopy for confirmation of peak identity

 

 

 

APPLICATIONS:

 

•   It is extensively used for the analysis of aromatic compounds present in food and beverages like esters, fatty acids, alcohols, aldehydes, terpenes etc.
•     It is accurate if used properly ,can measure pico moles of a substance in a 1ml liquid sample,or parts per Billon concentration in gaseous samples.
• Extensively  used in forensic science
•    The area under a peak is proportional to the amount of  analyte,  It results in quantitative analysis of the compound                                                                     

       REFERENCE:

        Modern  experimental biochemistry by Rodney Boyer.

    CONFIDENCE  IS THE KEY TO SUCCESS.