Chromatographic tools for analyzing and tracking non-ionic surfactants in the aquatic environment

This review describes the developments over the last few decades in the routine determination of two major types of non-ionic surfactants in environmental samples, i.e. alkylphenol ethoxylates (APE) and alcohol ethoxylates (AE). Commercial mixtures of these surfactants consist of several tens to hundreds of homologues, oligomers and isomers. Therefore, their identification and quantitation in the environment is complicated and cumbersome. The request for more specific analytical methods has prompted a replacement of all the separate steps in traditional, usually non-chromatographic methods of analysis of AP and APE by chromatographic tools. Thus, a 100-fold gain in detection limits has been achieved. Determination of AE and APE in aqueous samples is possible at the ppb level nowadays, when solid-phase extraction, including chromatographic cleanup, is applied, followed by liquid chromatography (LC). Reversed-phase LC resolves the various alkyl homologues, whereas normal-phase LC provides information on the ethoxylate oligomer distribution. Because of differences in (bio)degradation patterns observed in the aqueous environment between AE and APE, it is recommended to analyse AE by reversed-phase LC and APE by normal-phase LC. The more sophisticated hyphenated LC-MS techniques provide full information on isomer, oligomer and homologue distribution of both AE and APE.