In this study, construction of a new lanthanum selective disk electrode based on benzo-15-crown-5 (B15C5) as a neutral carrier has been described. The electrode has been composed of 2.5 mg of Benzo-15-crown5 as an ionophore, 7 mg of oleic acid (OA) as an additive, 60.5 mg of ortho-nitrophenyloctyl ether (NPOE) as a plasticizer, and 30 mg of polyvinyl chloride (PVC) as the membrane supporting matrix. The electrode shows a linear dynamic response in the concentration range of 5107 to 1102 M with a Nernstian slope of 19.5 mV per decade and a detection limit of 8.74107 M. It has a response time of <15 s and can be used for at least 5 months without any significant divergence in potentials. The electivity coefficients for mono, di, and trivalent cations indicate a good selectivity for La(III) ions over a large number of interfering cations. It could be used in a pH range of 3.06.0. The proposed electrode was applied as an indicator electrode in potentiometric titration of fluoride ion and also used for determination of F ion in mouthwash solution, tap water and toothpaste samples.

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