Activity 7: Chromatography: Key Read: Kenkel (p 299 - 389) and Harris, (Chip 22 - 25)
____ / ____ Score Name (last)______(first)______
For all questions, show your complete analysis and provide an explanation or justification.
Basic Chromatography 1. Consider a mixture of compound A, a somewhat polar liquid, and compound B, a somewhat nonpolar liquid. Tell which liquid, A and B,
would emerge from a chromatography column first under the following conditions and why:
a) A polar liquid mobile phase and a nonpolar liquid stationary phase
Compound A would emerge first because polar mixture components tend to dissolve more in the polar mobile phase and thus will
come through the column with the mobile phase and emerge first. B, being nonpolar, will tend to remain behind in the stationary
phase.
b) A nonpolar liquid mobile phase and a polar liquid stationary phase
B, since it is nonpolar it will emerge first since it will tend to dissolve more in the nonpolar mobile phase. This situation is opposite
to condition of part a.
2. The retention factor (or capacity factor), K of a compound is defined as K = ms/mM, that is K is the ratio of the masses of the
compound in equilibrium in the two phases. Show, from the information given in the corresponding chromatogram, that the
expression used k = (tR - tM) / tM is equivalent to this. Remember that for a given compound the relation between the retention
time tR, the time spent in the mobile phase tM (hold-up or dead time) and the time spent in the stationary phase ts, is as follow: tR
= tM + ts