Separation of Mixtures by Gas-Liquid Chromatography
Summary
Perhaps the most commonly used procedures for separating a mixture into its pure components
involve chromatography. Chromatographic procedures are used to separate multi-component mixtures
by partitioning their components between two phases. The first mobile phase constantly moves through
the second stationary phase. In this experiment, you will be using gas chromatography (GC) or, more
accurately, gas-liquid partition chromatography to resolve mixtures of the hydrocarbons pentane, hexane,
and heptane, CH3(CH2)nCH3 (n = 3, 4, and 5, respectively). In GC the compounds to be separated
partition (i.e., equilibrate) between a moving gas phase and a stationary liquid phase that coats an inert
support. As a result of this partitioning between the vapor phase and the solution phase, the individual
components in the gas phase successively elute from the GC column in order of decreasing solubility in
the liquid phase. The molecules that more strongly interact with (i.e., dissolve in) the liquid phase at the
operating temperature of the GC separation require longer times to elute from the column.