Spectrophotometric determination of low levels of anionic surfactants in water by solvent extraction in a flow injection system

Abstract

An approach to automation, in routine control, for the determination of anionic surfactants in river water and treatment plant water in the concentration range 0.04–3.5 µg ml^–1 using a continuous solvent extraction process with flow injection analysis, is described. The method is based on an ion-pair extraction reaction with Methylene Blue in chloroform. The separation of both phases is accomplished by means of a membrane phase separator and detection is based on injection of the coloured organic phase into a chloroform stream which passes to the detector. Methanol was added to the organic phase in order to enhance the extraction process and to ensure efficient extraction of the various anionic surfactants. A number of anionic species and non-ionic surfactants have been tested as possible interferents. The results obtained for samples of river water show good agreement with those obtained with the Methylene Blue batch method.