Determination of terbium(III) ions in phosphate rock samples by a Tb3+–PVC membrane sensor based on N, N-Dimethyl-N′, N″-bis(4-methoxyphenyl)phosphoramidate

A poly (vinyl chloride)-based membrane of N, N-Dimethyl-N′, N″-bis(4-methoxyphenyl)phosphoramidate (DMP) as a neutral carrier was prepared and investigated as a Tb3+-selective electrode. This electrode constructed with sodium tetraphenylborate (NaTPB) as the anion excluder and 2-nitrophenyl octyl ether (NPOE) as the plasticizer. Its performance was found to be the following: a Nernstian slope of 19.7 ± 0.4 mV per decade across a broad range (1.0 × 10− 6 to 1.0 × 10− 1 M); a detection limit of 8.0 × 10− 7 M between the pH values of 3.5 and 8.0; additionally, the response time was about 10 s; usage of more than 2 months without any potential divergence; good Tb3+ selectivity over a wide variety of other metal ions. The membrane sensor was applied to the Tb3+ recovery from different water samples, determination of fluoride ions in mouth wash samples and the determination of Tb3+ in phosphate rock samples. It was also used as an indicator electrode in the potentiometric titration of Tb3+ ions with EDTA.