HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC ANALYSIS OF POLYDISPERSE ETHOXYLATED NONIONIC 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 ba sis of the number of ethoxylate (EO) groups per molecule. This method is demonstrated to separate ethoxylated homologues of broadly distribu ted linear alcohol ethoxylates and alkylphenol ethoxylates, with numbe rs of EO groups ranging from 3 to 50 or greater. This method presents a significant advance in non-ionic surfactant analysis because it perm its direct injection of aqueous samples, eliminating the need for exte nsive sample preparation. The method discussed here is optimized for u se with an evaporative light scattering detector (ELSD), but works equ ally well with UV absorbance or fluorescence detectors for the analysi s of surfactants with chromophores. ELSD and UV detector operating con ditions and calibration methods are discussed.