Abstract
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.
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