By Sunil Bhardwaj


A very important and quite often a difficult step in chemical analysis is the separation of the desired constituent in an analytical sample. The difficulties are all the more serious if the sample is a mixture of volatile liquids with close boiling points. Gas chromatography, discovered by Martin and Synge, has made the task of separating such volatile mixtures comparatively easy.

Principles: Gas chromatographic separations are based on the differences in the extent to which solutes are partitioned between the stationary phase and the mobile phase.

GCWhen gaseous sample is inserted in the column which contain stationary phase solid or liquid the components of samples are retained by the stationary phase on different positions when we pass the eluent gas the component which is less strongly retained is eluted out first.

Consider a mixture containing three components A, B and C is to be separated by GLC. A very small quantity is injected into the front end of the column. Each component of the mixture in its passage through the column is retarded by the stationary liquid phase. The degree of retardation of a component depends upon the partition coefficient of that component in the liquid phase.

I.e. the tendency of the component to dissolve in the liquid (Stationary). Component (A) dissolves to the maximum extent, while component (C) dissolves to the least extent Component (C) emerges first along with the carrier gas followed by (B) and (A). The signals given by the detector are recorded. The development of the chromatogram can be obtained from grapher.

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