Continuous TLC as a pilot technique for optimization of gradient HPLC. 1. Theoretical considerations for stepwise gradient TLC with binary mobile phase

Equations describing gradient elution in TLC, with a mobile phase of a constant composition in each step, have been derived. These equations are useful for calculating retention volumes from isocratic TLC data. Equations originally derived for gradient HPLC were adapted for TLC. The validity of the equations has been experimentally verified. The satisfactory agreement between experiment and theory for binary mobile phase composed of methyl ethyl ketone and n‐heptane suggests that TLC can be used as a pilot technique for gradient HPLC.