A flow immunoassay for alkylphenol ethoxylate surfactants and their metabolites—questions associated with cross-reactivity, matrix effects, and validation by chromatographic techniques

Abstract

This paper describes the application and evaluation of a competitive enzyme flow injection immunoassay (EFIIA) for screening of alkylphenol ethoxylate (APEO) surfactants in different water samples based on a generic immunoassay system previously developed (see E. Burestedt, C Nistor, U. Schagerlöf and J. Emnéus, Anal. Chem., 2000, 72, 4171–4177). The detection limits for octylphenol ethoxylates (OPEOs), nonylphenol ethoxylates (NPEOs), and nonylphenol (NP) were 0.5 µg l⁻¹, between 2 and 3 µg l⁻¹, and 50 µg l⁻¹, respectively, with a sample throughput of 6 h⁻¹ (i.e., for triplicate analysis of each sample). Different OPEOs and NPEOs were highly cross-reactive within the assay, with sensitivities in the same order of magnitude for all the ethoxylates tested, thus the result obtained by the EFIIA method could be used as an “alkylphenol ethoxylate index”. No or minor matrix effects with recoveries between 70–120% for the reference analyte NPEO₁₀ in tap, and surface water, and acceptable for rainwater, were observed. Influent and effluent surfactant containing wastewater samples were analysed by EFIIA, LC-MS, LC-Fluoresence (LC-FL), and a commercial microplate ELISA. High recoveries for different concentrations of APEO₁₀ spiked into a 200 times diluted raw influent and effluent wastewater were achieved with the EFIIA method, however, the found APEO content of the same diluted wastewater samples, before spiking, could not be correlated directly to the chromatographic result by any of the immunoassays, and the possible reasons for this are discussed. The same trend of decreasing APEO content from influent to effluent wastewater could, however, be followed for all methods employed.