Anion-Selective Electrodes Based on Polyvalent Metal Complexes

Anion-Selective Electrodes Based on Polyvalent Metal Complexes

Akio Yuchi¹

¹ Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya-shi, Aichi 466-8555

(Received 28 September 2005, Accepted 11 November 2005)

The performances of metal complexes and organometalic compounds containing polyvalent metal ions were studied as carriers of liquid membrane anion-selective electrodes from both fundamental and practical view points. 1) The high selectivities of simple dialkyltin(IV) compounds to phosphate and to a-hydroxycarboxylates were ascribed to formation of partially hydrolyzed polynuclear complexes, where these anions interacted with two Sn(IV) centers and were shielded from the solvent by alkyl groups projected from Sn(IV). This is the first evidence that the self-assembling reactions of a carrier and a sample anion create novel selectivities in potentiometry with liquid membrane anion-selective electrodes. 2) Tetraphenylporphine (H₂tpp) complexes of Ti(IV), V(IV), Zr(IV), Hf(IV), Nb(V), and Ta(V) were prepared and evaluated as carriers of ISEs. Among a series of Zr(IV)-tetraphenylporphine complexes, cationic dimers, ([Zr₂(OH)₃(tpp)₂],X), showed the selectivity characteristic of the ion-exchange process. The response was smaller for the cationic dimers containing X^- of higher lipophilicities. In contrast, neutral monomers, [ZrX₂(tpp)], showed the selectivity indicating contribution of ligand-exchange reactions. Among the neutral monomers, [ZrCl₂(tpp)] was easily hydrolyzed to give [Zr(OH)Cl(tpp)], which showed an appreciable response to carboxylates. The response slowly deteriorated by replacement of chloride with hydroxide but was recovered in a reversible manner by conditioning the membrane with concentrated hydrochloric acid. The monomer, [Zr(OH)₂(tpp)], was proposed as a carrier of an excellent citrate-selective electrode. 3) The neutral dimer [Nb₂O₃(tpp)₂] rapidly reacted with phosgene to give [NbOCl(tpp)]. This reaction was successfully applied to the spectrophotometric monitoring of the spontaneous formation of phosgene in chlorinated hydrocarbons. 4) Potentiometric performances were briefly described about the Zr(IV)-dodecyliminodiacetate complex, the Ge(IV)-nitrilotriphenol complex, and naphthylboronic acid. All these results were discussed in terms of multi-points recognition, self-assembly, charges on carriers, additives, conditioning and life-time.

Keywords : ion-selective electrode; carrier; anion; citrate; two-phase reaction.