Copper(II)-selective membrane electrode based on hydrotris(3-isopropylpyrazolyl)methane in a poly(vinyl chloride) matrix Original Research Article

Polypyrazolylmethanes, represented by the general formula H4−nC(pz)n (pz: 1-pyrazolyl), form a six-membered MN4C chelate ring of a shallow boat configuration, acting as tridentate or bidentate ligands. We have developed novel ion-selective membrane electrodes based on polypyrazolylmethanes and report the first results of their use here. HC(pz)3 (1), HC(3,5-Me2pz)3(2), HC(3-Phpz)3 (3), HC(3-iPrpz)3 (4), HOCH2C(pz)3 (5), and C(pz)4 (6) were prepared as described in the literature and incorporated as an ionophore in PVC membrane. The selectivity of the electrodes changed with the substituents of polypyrazolylmethanes. The electrodes of 3, 4 and 6 were selective for Cu2+ at pH 5.5. The electrode of 5 was selective for Pb2+ and Cu2+ at pH 5.5. Since the selectivity coefficient log KCu,Mpot of electrode 4 was less than −6.4 for the divalent cations, it was most selective for Cu2+ among Cu2+ selective electrodes ever reported. The detection limit and dynamic range for Cu2+ were 2×10−6 and 10−6 to 5×10−3 M, respectively. The electrode 4 showed rapid response time (∼10 s) and reproducible results for more than 4 months, and successfully applied to potentiometric titration of Cu2+ with EDTA.