Experiment 2 – Chem 276 – Fall Semester 2010 Page 1 of 5
Experiment 2 - Thin Layer Chromatography
Introduction
Chromatography is an experimental technique by which a mixture of compounds can be
separated into its individual components. In thin layer chromatography, there is a
stationary phase as well as a mobile phase. For this experiment, the TLC plate consists of
an aluminum backing on which is placed a thin layer of silica gel. The silica gel is the
stationary phase. The eluding solvent is the mobile phase which carries with it the
components of the mixture. Thin layer chromatography is used mostly for analytical
purposes. Microgram to picogram quantities can be separated by this technique and then
characterized by their Rf value.
The retention factor, or Rf, is defined as the distance traveled by the compound divided
by the distance traveled by the solvent.
Rf=distance traveled by compound
distance traveled by solvent front
In the example shown below, a compound travels 16.2 cm while the solvent front travels
23.0 cm, the Rf is 0.704:
Rf=
solvent front
origin
new position
of compound
16.2 cm
23.0 cm
16.2
23.0 =0.704
The Rf for a compound is a constant from one experiment to the next only if the
chromatography conditions below are also constant:
solvent system
adsorbent
thickness of the adsorbent
amount of material spotted
temperature
