Determination of polyoxyethylene alkylphenyl ether non-ionic surfactants in waters

Abstract

A method is proposed for the determination of polyoxyethylene alkylphenyl ethers, RO(CH₂CH₂O)_nH (where R is an alkylphenyl group), at the 1–0.1 mg l^–1 level in waters. The method is based on the spectrophotometric determination of the complexes of the polyethers with the sodium cation after extraction as picrates into 1,2-dichloroethane. The number-average degree of polymerisation (n) is evaluated by thin-layer chromatography or by gas chromatography.

The method was tested on commercial compounds that have R =p-tert-nonylphenyl (3.3 ⩽n⩽ 21.5). For typical surfactants (6.5 ⩽n⩽ 21.5) the proposed method is about eight times more sensitive than that based on the ammonium tetrathioisocyanatocobaltate(II) reagent and it gives results for the absolute concentration with an accuracy ranging from –6 to +8 per cent. in the indicated interval of n. The precision was evaluated from the analysis of waste waters. A few interferences are discussed.