In partition mode, the stationary phase is assumed to have a large
active surface area and P=Cs/Cm. Cs is the concentration of a solute
in the stationary phase. Cm is the concentration of a solute in the
mobile phase. In competition mode, the stationary phase
has a limited number of active sites and P=Cs/(Cm S). S is the concentration
of unoccupied active sites on the stationary phase. This is equivalent to
a Langmuir absorption isotherm.
To get comparable retention between a partitioning
run and a competitive run, divide the partition coefficient for the partitioning
run by the concentration of stationary sites. For example,
if the partitioning partition coefficient for A is 0.1 and the
concentration of stationary sites is 10 equiv/L, then divide the partition
coefficient by 10 equiv/L to get the competitive partition coefficient, P(A)=0.01.
Colby College Chemistry, Thomas W. Shattuck