摘要：Collaborative studies on the determination of anionic surfactants in water were carried out to establish a method contributed to the Standard Method of Analysis of Hygienic Chemists authorized by the Pharmaceutical Society of Japan. The proposed methods were based on the colorimetric and atomic absorption spectrophotometric methods using bis[2-(5-chloro-2-pyridylazo)-5-diethylaminophenolato]cobalt[III]chloride (Co-PADAP) as a chelating agent. An adequate volume of a water sample containing 3-30μg (colorimetric method) or 0.1-5μg (atomic absorption method) of surfactants was taken in a separatory funnel. Two ml of 5 N-HCl or 2 N-H2SO4 and 1 ml of 0.04% Co-PADAP solution were added to the sample solution and mixed for a few seconds. After allowing to stand for 1 min, 10.0 ml of benzene was added to the solution and shaken for 1 min. The absorbance of the separated benzene layer at 560 nm was measured in the colorimetric method, while the layer was subjected to atomic absorption spectrophotometry when the concentration of surfactants in water was lower than 0.06 mg/l. When dodecylbenzenesulfonate (LAS) was used as a standard compound and recovery tests were performed for river water, satisfactory results were obtained. The limits to obtain accurate assayed values were 0.06 mg/l for the colorimetric method and 0.0001 mg/l for the atomic absorption spectrophotometric method, respectively.
