Analytical Sciences

New Cadmium(II)-Selective Electrode Based on a Tetraazacyclohexadeca Macrocyclic Ionophore

Ashok Kumar SINGH, Puja SAXENA, and Rupam SINGH

Department of Chemistry, Indian Institute of Technology-Roorkee, Roorkee-247 667, India

A poly(vinyl chloride)-based membrane of 3,4:11,12-dibenzo-1,6,9,14-tetraazacyclohexadecane with sodium tetraphenyl borate (NaTPB) as an anion excluder and dibutylphthalate (DBP), dibutyl(butyl)phosphonate (DBBP), tris(2-ethylhexyl)phosphate (TEHP) and tributyl phosphate (TBP) as a plasticizing solvent mediator was prepared and investigated as a Cd²⁺-selective electrode. The best performance was observed with the membrane having a ligand-PVC-DBP-NaTPB composition of 2:25:60:1, which worked well over a wide concentration range (1.6 × 10^-6 - 1.0 × 10^-1 M) with a Nernstian slope of 29.5 mV per decade of activity between pH 2.0 - 6.0. This electrode showed a fast response time of 13 s and was used over a period of 4 months with good reproducibility (S = 0.4 mV). The selectivity coefficient for mono-, di- and trivalent cations indicated excellent selectivity for Cd²⁺ ions over a large number of cations. Anions such as NO₃^- and SO₄^2-, did not interfere. The membrane sensor has been successfully used to determine Cd²⁺ in real samples.

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