This study concerns the evaluation of ionophoric properties of a functionalized calix[4]arene, named 5,17-bis(diphenylphosphinoyl)- 25,26,27,28-tetrapropoxycalix[4]arene (Calix), by its application as a sensing material in an erbium(III)-PVC membrane potentiometric sensor. A membrane formed by 30% PVC, 65% dioctyl phthalate (DOP) as plasticizing solvent mediator, 2% sodium tetraphenyl borate (NaTPB) as ion excluder, and 3% of Calix as ionophore shows the best performance of the sensor. The prepared sensor presents a nearly Nernstian response (a slope of 20.0 \pm 0.5 mV/decade) over a concentration range of 1 \times 10-7--1 \times 10-3 M of erbium ions, with a limit of detection of 3.8 \times 10-8 M. Its potential response was independent of pH variation in the relatively wide range 4.5--6.5. The dynamic response time of the electrode to achieve a steady potential was found to be about 7 s. The selectivity of the sensor towards erbium ions with respect to several mono-, di-, tri-, and tetravalent metal ions was examined. The prepared sensor can be used for 3 months without considerable divergences in potential response. The performance of the sensor was examined as an indicator electrode for complexometric titration of erbium solutions by EDTA.

This study concerns the evaluation of ionophoric properties of a functionalized calix[4]arene, named 5,17-bis(diphenylphosphinoyl)- 25,26,27,28-tetrapropoxycalix[4]arene (Calix), by its application as a sensing material in an erbium(III)-PVC membrane potentiometric sensor. A membrane formed by 30% PVC, 65% dioctyl phthalate (DOP) as plasticizing solvent mediator, 2% sodium tetraphenyl borate (NaTPB) as ion excluder, and 3% of Calix as ionophore shows the best performance of the sensor. The prepared sensor presents a nearly Nernstian response (a slope of 20.0 \pm 0.5 mV/decade) over a concentration range of 1 \times 10-7--1 \times 10-3 M of erbium ions, with a limit of detection of 3.8 \times 10-8 M. Its potential response was independent of pH variation in the relatively wide range 4.5--6.5. The dynamic response time of the electrode to achieve a steady potential was found to be about 7 s. The selectivity of the sensor towards erbium ions with respect to several mono-, di-, tri-, and tetravalent metal ions was examined. The prepared sensor can be used for 3 months without considerable divergences in potential response. The performance of the sensor was examined as an indicator electrode for complexometric titration of erbium solutions by EDTA.