# HPLC method for salicylic acid

Salicylic acid is a relatively polar compound hence I thought that normal phase would be preferred as the stationary phase of normal phase is polar. However, it is said that reverse phase would be the preferred option instead.

Can somebody explain to me why reverse phase HPLC is preferred for salicylic acid? And would reverse phase produce better graphs/results than normal phase?

To avoid that, you have to force the equilibrium to the acid form, which is also more apolar, so the reverse phase makes even more sense. For this, it is sufficient to add a small amount of acid to the water used in the mobile phase. Very often, 0.1% formic acid is enough. Sometimes it is required to use higher concentrations up to 1%. If you need a higher $\mathrm pK_\mathrm a$, you can use trifluoroacetic acid instead.