High-performance liquid chromatographic analysis of polydisperse ethoxylated non-ionic surfactants in aqueous samples

An adsorption HPLC method using traditionally reversed-phase solvents and a hybrid column/precolumn has been developed for the quantitative separation and analysis of ethoxylated non-ionic Surfactants on the basis of the number of ethoxylate (EO) groups per molecule. This method is demonstrated to separate ethoxylated homologues of broadly distributed linear alcohol ethoxylates and alkylphenol ethoxylates, with numbers of EO groups ranging from 3 to 50 or greater. This method presents a significant advance in non-ionic surfactant analysis because it permits direct injection of aqueous samples, eliminating the need for extensive sample preparation. The method discussed here is optimized for use with an evaporative light scattering detector (ELSD), but works equally well with UV absorbance or fluorescence detectors for the analysis of surfactants with chromophores. ELSD and UV detector operating conditions and calibration methods are discussed.