Simulating phenol high-performance liquid chromatography retention times as the pH changes: Mobile phase pH versus buffer pH

The HPLC retention times of several substituted phenols have been measured and simulated using Advanced Chemistry Developmentʹs LC simulator, using 50% acetonitrile (ACN) as the mobile phase. For alkyl- and nitro-substituted phenols, the quality of the simulation improves when pH of the mobile phase is estimated and used in the simulation. Simply using the pH of the buffer gives simulation results that are not as close to the actual retention times. However, the opposite is the case for halogenated phenols. The pKa values in 50% ACN for some of these phenols have also been determined, which tend to be one unit higher than the aqueous pKa values reported in the literature.