Basic principle of Gas Chromatography

• Gas chromatography is an instrumental method for separation and identification components of a mixture. Gas is used as mobile phase in chromatography so it known as the gas chromatography. The stationary phase can be either a solid or liquid.

•  In gas chromatography volatile component can also be separated and analyzed which can not be possible with liquid chromatography.

•  Gas chromatography involves sample mixture which  vaporized and then entrained by carrier gas.The sample used in GC should be capable of being converted into a gas at temperature of column.

• The gas mixture is passed through a glass or metal tube which is known as column containing a stationary phase The phases are chosen such that components of the sample have differing solubility in each phase.

• Various components of a mixture travel through the stationary phase at different speeds which causes them to separate. Since different components emerge from the column at different times, they can be identified by a detector at the outlet of the column.

•  A GC system generates a plot of the detector signal as a function of time. This plot is referred to as a chromatogram. Different peaks on a chromatogram correspond to different components and the areas under these peaks can be used to quantify the mole fraction of each component.

•  In Gas chromatography the stationary phase can be either a solid or liquid.

• When stationary phase is in gas chromatography is known as the gas solid chromatography(GSC).Column which contain particle of solid which packed into column.In GSC separation is based on relative adsorption of sample component. 

• Gas-solid chromatography is relatively rare, but it is used to separate atmospheric gases.  

• Gas-liquid chromatography (GLC): when stationary phase is liquid the chromatography is known as gas liquid chromatography. The liquid may be coated as a thin film on the wall of column or liquid may be coated on solid particle of solid which packed into the column.  
• In GLC, separation can be based on either relative solubility of sample components in stationary phase or combination of relative solubility in stationary phase and adsorption on solid support of stationary phase.

•  Gas-liquid chromatography is most widely used in pharmaceutical industries.