Fluorescence optical sensing of anionic surfactants using a lactone-form Rhodamine B membrane

We report on the development of an optical fluorescence sensor based on the lactone-form Rhodamine B (L-RB) for the detection of an anionic surfactant (AS). The sensor was prepared by embedding the L-RB in a 2-nitrophenyloctyl ether-plasticized poly (vinyl chloride) (PVC) membrane. The optical fluorescence response to AS occurred due to ion-pair coextraction of an AS and a proton into the PVC membrane. The extracted AS enlarges fluorescence of the PVC membrane (λ_ex = 559 nm, λ_em = 584 nm). The optical fluorescence membrane responds to anionic surfactants, such as dodecylbenzenesulfonate in the concentration range from 0.50 to 5.0 µM. The coexistences of NaCl, KCl, CaCl₂, MgCl2, Na₂SO₄ and NaNO₃ at 100 times, a nonionic surfactant (Triton X-100) at 10 times excess to AS did not interfere with the determination of AS within an error of 10 %. The recovery of AS added to environmental water samples was roughly 91 - 104 %. The result indicates that there is small matrix effect on the determination of AS in environmental water samples, and that the present optical fluorescence sensor is applicable for the determination of AS in environmental water samples such as river water and tap water.