COMPARISON OF VARIOUS STATIONARY PHASES FOR NORMAL-PHASE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY OF ETHOXYLATED ALKYLPHENOLS

Unmodified silica and chemically bonded diol, nitrile and amino phases were tested as column packings for normal-phase liquid chromatographic separations of ethoxylated alkylphenols in mobile phases consisting of aliphatic alcohol(s) and a non-polar hydrocarbon. The performance of unmodified silica is improved when ethanol is used instead of propanol in binary mobile phases or when ethanol-propanol-aliphatic hydrocarbon ternary mobile phases are applied. Diol and nitrile bonded phases show regular retention behaviour only in mobile phases with a low content of propanol, where 6-8 ethoxymers can be resolved in a reasonable time. In propanol-rich mobile phases, a mixed retention mechanism causes a non-linear increase in log k′ with increasing number of oxyethylene units, which hinders the prediction of retention by calculation and deteriorates the separation of the individual oligomers in propanol-n-alkane mobile phases. The amino-bonded stationary phase shows regular retention behaviour even for higher ethoxymers in mobile phases containing high proportions of propanol in n-alkane, so that the capacity factors can be predicted by calculation. The amino-bonded phase offers better separation possibilities for the individual ethoxymers than the other stationary phases tested, in both the isocratic and gradient modes of elution. © 1990.