The Purnell equation is an equation used in analytical chemistry to calculate the resolution R_s between two peaks in a chromatogram.^{[1] [2]}

${\displaystyle R_{s}={\frac {\sqrt {N_{2}}}{4}}\left({\frac {\alpha -1}{\alpha }}\right)\left({\frac {k'_{2}}{1+k'_{2}}}\right)}$

where

R_s is the resolution between the two peaks

N₂ is the plate number of the second peak

α is the separation factor between the two peaks

k '₂ is the retention factor of the second peak.

The higher the resolution, the better the separation.