Purnell equation

The Purnell equation is an equation used in analytical chemistry to calculate the resolution R_s between two peaks in a chromatogram:^[1][2][3]

$R_s = \frac{\sqrt{N_2}}{4} \left ( \frac{\alpha - 1}{\alpha} \right ) \left ( \frac{k'_2}{1 + k'_2} \right )$

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.

References

1. Miller, J. M., Chromatography: Concepts and Contrasts, second edition, John Wiley & Sons, Inc., Hoboken, NJ, USA, 2005.
2. Dean, J. R. et al., Practical Skills in Chemistry, first edition, Pearson Education Ltd., Harlow, UK, 2002, p. 205–224.
3. C. Legido-Quigley, HPLC theory