OPTIMIZATIONS OF HPLC CONDITIONS TO ANALYZE WIDELY DISTRIBUTED ETHOXYLATED ALKYLPHENOL SURFACTANTS

Commercial ethoxylated alkylphenol surfactants are always a mixture of oligomers with different ethylene oxide number (EON). The different oligomers can be separated by various HPLC techniques. Isocratic mode with mixed solvent on silica column allows to separate oligomers up to EON = 10; gradient programming moves the limit up to EON = 15. For higher EON values (up to 25) a NH2 column has to be used, either with isocratic or gradient mode. Applications to the analysis of microemulsion systems and to the separation of tributyl phenol ethoxylates are discussed. Extreme separation of wide range EON distribution is attained with two columns (Si and NH2) in series, and a solvent programming.