Novel Tm(III) Membrane Sensor Based on 2,2'-Dianiline Disulfide and Its Application for the Fluoride Monitoring of Mouth Wash Preparations

In this work the construction of a novel poly(vinyl chloride) membrane sensor based on 2,2'-dianiline disulfide (DADS) as a neutral carrier, o-nitrophenyloctyl ether (NPOE) as a plasticizer and sodium tetraphenyl borate (NaTPB) as an anionic site with unique selectivity towards Tm(III) ions is reported. The electrode has a linear dynamic range between 1.0 x 10 -6 and 1.0 x 10 -2 M, with a nice Nemstian slope of 19.5 ± 0.3 mV per decade and a detection limit of 4.0 x 10 -7 M at the pH range of 4.8-8.5. It has a very fast response time (<15 s) in the whole concentration range, and can be used for at least 4 weeks without any considerable divergence in the electrode potentials. The proposed sensor revealed comparatively good selectivity with respect to most common metal ions, and especially lanthanide ions. It was used as an indicator electrode in the potentiometric titration of Tm(III) ions with EDTA and in direct determination of concentration of Tm(III) ions in binary mixtures. It was also applied in determination of fluoride ions in mouth wash preparations.