where (KA) is the distribution coefficient of the first eluted solute between the two phases.
Figure 17. Chromatogram Showing Two Resolved Peaks
Thus, if resolution is achieved when the peak maxima of the pair of solutes are (4s) apart, then
Rearranging,
Dividing
through by (vm), and noting that 
,
The separation ratio, (a), between the two solutes, has been defined as
