Continuous liquid–liquid extraction with on-line monitoring for the determination of anionic surfactants in waters

Abstract

A continuous liquid–liquid extraction method for controlled preconcentration of anionic surfactants and their determination in water samples is proposed. The methodology is characterized by its automated performance and simultaneous extraction, reaction and photometric detection, simplifying previous approaches. An organic plug (volume 200 µl) containing the reagent is placed and retained at the detection point while a large volume of sample (aqueous phase) is passed through it. The gradual enrichment of the organic phase with the analyte is continuously monitored. The ion pair reaction between the anionic surfactants and Methylene Blue in chloroform was used. A determination limit of 20 ng ml^–1, a relative standard deviation of 6.7% and a sample throughput of 20 h^–1 were achieved. The proposed method was successfully applied to the determination of surfactants both in synthetic and real water samples.