A new highly sensitive surfactant-selective liquid membrane electrode based on 1, 3-didecyl-2-methyl-imidazolium-tetraphenylborate (DMI-TPB) ion-exchange complex as a sensing material has been prepared [4]. In the investigations described DMI-TPB sensor was tested for determination of anionic surfactants in effluents. The sensor responded fast and exhibited a Nernstian response. Its main application was indication of the end-point in ion-pair surfactant potentiometric titrations. DMI-TPB sensor exhibits excellent selectivity performances for DS over almost all organic and inorganic anions investigated. The organic and inorganic anions commonly used in surfactant based industrial and household formulations, do not interfere in anionic surfactant potentiometric determination. The mixed solution method  5 has been used for measurement of selectivity coefficients. The sensor is used for titration of diluted industrial detergent products without pretreatment, except for those containing complexed surfactant mixture, where pH adjustment was needed. It was used for the monitoring of anionic surfactants in industrial wastewaters too, without pretreatment, except filtration when necessary. The equivalence points of slightly distorted titration curves or those with poorer and noisy inflexions can be calculated using multiple point parabola fit. The results obtained agree satisfactory with standard extraction-spectrophotometric MBAS (Methylene Blue Active Substance) method [6] for low concentration of anionic surfactants in effluents and surface waters. The average lifetime of the membrane was at least six months, depending on the nature of the analytes.

Chemistry