Analysis of nonionic surfactants in bench‐scale biotreater samples

The effluents and activated sludges used in benchscale biotreater units have been analyzed for nonionic alcohol ethoxylates and their residues. Separate bench‐scale units were fed linear alcohol ethoxylates (AE), highly branched and branched nonylphenol ethoxylates. Effluents and sludges were first pretreated by a foam sublation technique to provide a gross separation of surfactants from the environmental matrix. This step was followed by normal‐phase high‐performance liquid chromatography (HPLC) with either fluorescence detection (FD) or evaporative light‐scattering detection (ESLD). The AEs were derivatized with phenylisocyanate and analyzed by normal‐phase HPLC coupled with FD. At extremely low surfactant levels, pretreatment of large sample volumes resulted in interferences on derivatization. Hence, a normal‐phase HPLC method with ELSD was developed. Although some interferences do appear using ELSD, this method appears to be a more viable alternative to derivatization/FD for very low levels of AE. HPLC with FD and ELSD detection methods are more quantitative and provide information on the polyoxyethylene chain than is possible with traditional methods like cobalt‐thiocyanate active substance.