Novel ytterbium(III) selective membrane sensor based on N-(2-pyridyl)-N′-(2-methoxyphenyl)-thiourea as an excellent carrier and its application to determination of fluoride in mouth wash preparation samples

The construction, performance, and applications of a novel ytterbium(III) sensor based on N-(2-pyridyl)-N '-(2methoxyphenyl)-thiourea (PMT), as an excellent carrier, in plasticized poly(vinyl chloride) PVC matrix, is described. The influences of membrane composition and pH on the potentiometric response of the sensor were investigated. The sensor exhibits a nice Nernstian response for Yb(III) ion over a wide concentration range of 4 decades of concentration (1.0 x 10(-6) -1.0 x 10(-2) M), and a detection limit of 5.0 x 10(-7) M. The response time of the electrodes is between 8 and 70 s, depending on the concentration of ytterbium(III) ions. The proposed sensor can be used for about 8 weeks without any considerable divergence in potential. The sensor revealed very good selectivity for Yb(III) in the presence of several metal ions. The best performance was observed for the membrane containing; 30% PVC, 59% o-nitrophenyloctyl ether (NPOE) as solvent mediator, 7% PMT, and 4% sodium tetraphenyl borate (NaTPB). It was successfully applied as indicator electrodes in the potentiometric titration of Yb(III) with EDTA and for the determination of fluoride ion in two mouth wash formulations. The proposed La(III) sensor was found to work well under laboratory conditions. It was also used as an indicator electrode in titration of a 1.0 x 10(-4) M of Yb(III) with a standard EDTA solution (1.0 x 10(-2) M). It was also used for determination of Yb(III) ion in Xenotime.