Retention characteristics of six sets of ionizable substituted benzene
isomers have been measured on a porous graphitic carbon column using
buffered aqueous eluents containing 35% acetonitrile. The elution orde
rs varied with the different types of substituents on the benzene ring
and were not readily predictable from the known structures of the iso
mers. Over the range of mobile phase between pH 2 to 9.4, the retentio
n of the solutes was correlated directly with their degree of ionizati
on, with the ionized form being least retained. An interpretation of t
hese data was suggested based on the solute molecular orientation effe
ct induced by the competing interactions of solute with adsorbent and
solvent.