Separation and identification of nonylphenylethylene oxide oligomers by high-performance liquid chromatography with UV and mass spectrometric detection

Nonylphenylethylene oxide surfactants were separated on an alumina column using an ethylene oxide-n-hexane mixture as the mobile phase, and UV and MS detection. Several well separated, large peaks and some small, partly separated peaks were detected. It was found that the main fractions elute log-equidistantly and they correspond to the nonylphenylethylene oxide oligomers with a given number of ethylene oxide units, and the small peaks contain isomers, probably surfactants with different positions of the nonylgroup at the phenyl ring. The method validation showed no significant differences between the intra-day and inter-day values of the area percentages and their standard deviations, showing the good reproducibility of the determination of the area percentages during at least three consecutive days. Significant differences were found between the intra-day and inter-day values of the standard deviation of the retention times, which indicates that the determination of the retention time is less reproducible than that of the area percentages. (C) 1998 Elsevier Science B.V. All rights reserved.