An analytical method for polyoxyethylene-type nonionic surfactants is proposed. It was found that the surfactants are preconcentrated by solvent extraction with toluene and many coexisting substances such as LAS or humic acid are washed out at the same time. Those in the toluene can extract cobalt(II) from aqueous thiocyanate solution. By determination of the metal with spectrophotometry as 4-(2-pyridylazo-)-resorcinolato complex, the concentration of the surfactants can be measured. Use of toluene as the solvent is useful not only for the purification of the surfactants from many interferences but also for the easier treatment of waste solvents in comparison to i.e. halogenated organic solvents.
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Kazuho Inaba (1987) studied this question.
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