Photometric determination of anionic surfactants with a flow-injection analyzer that includes a chromatomembrane cell for sample preconcentration by liquid-liquid solvent extraction.

Chromatomembrane cells proved to be applicable to flow-injection analysis whenever computer-operated manifolds for liquid-liquid or liquid-gas extraction procedures were required. Proceeding in accordance with the Methylene Blue method the determination of anionic surfactants was studied by applying the chromatomembrane cell for preconcentration and extraction of the ion-pair complex being formed. Spectrophotometric detection at 650 nm was made possible by using a flowthrough cell within a range of 0.02-5.0 mg dodecylsulfate per liter of water. The absorbance was found to respond proportionally to the product of preconcentration time and surfactant concentration, its slope factor being calculated with +/- 3% standard deviation. A mechanism for the preconcentration cycle inside the cell is suggested.