Determination of traces of polyoxyethylene non-ionic surfactants in water by solvent extraction-spectrophotometry

Abstract

The determination of traces of polyoxyethylene non-ionic surfactants (APE) in water is based on the formation of a complex between APE and sodium picrate. The complex is extracted into 1,2-dichloroethane and the absorbance of the solvent phase is measured at 378 nm. Quarternary ammonium surfactants and iron(III) caused positive errors, but the interference due to iron(III) was effectively masked with CyDTA. Humic acids, anionic surfactants, common cations and anions did not interfere. For general type APE (n=8–13) the apparent molar absorptivities of the picrate complexes were 5–7 times larger than those of cobalt thiocyanate complexes. Various polyethoxylated compounds in the range ofn from 9 to 85 in the same quantity were almost the same in absorbance; recoveries of APE were about 93–107%. Therefore this method is quite usable. As little as 0.04 ppm can be determined. In a river water sample 0.04–0.05 ppm and in another case 0.34 ppm of APE were found.