Comparative Study of Holmium (III) Selective Sensors Based on Thiacalixarene and Calixarene Derivatives as an Ionophore

摘要

The two chelates based on calix[4]arene and thiacalix[4]arene have been synthesized and used as neutral ionophores for preparing PVC based membrane sensor selective to Ho~(3+) ion. The addition of potassium tetrakis(4-chlorophenyl)borate (KTpClPB) and various plasticizers, viz., NDPE, o-NPOE, DOP, TEP and DOS have been found to improve significantly the performance of the sensors. The best performance was obtained with the sensor no. 6 having membrane of L2 with composition (w/w) ionophore (2%): KTpClPB (4%): PVC (37%): NDPE (57%). This sensor exhibits Nernatian response with slope 21.10 ± 0.3 mV/decade of activity in the concentration range 3.0 x 10~(-8) -1.0 x 10"2 M Ho~(3+) ion, with a detection limit of 1.0 x 10~(-8) M. The proposed sensor performs satisfactorily over a wide pH range of 2.8-10, with a fast response time (5 s). The sensor was also found to work successfully in partially non-aqueous media up to 25% (v/v) content of methanol, ethanol and acetonitrile, and can be used for a period of 4 months without any significant drift in potential. The electrode was also used for the determination of Ho~(3+) ions in synthetic mixtures of different ions and the determination of the arsenate ion in different water samples.