Evaluation of zirconium(IV) complex with N-dodecyliminodiacetate as an anionophore for ion-selective electrodes.

chemistry of anion recognition is now being uncovered and producing a variety of practical applications, including separation and sensing. 1–3 The use of Lewis acid-base interactions is a promising approach in this respect. We previously found that zirconium(IV) could be immobilized on a chelating polymer, having an iminodiacetate (IDA) group (–LH2), as a 1:1 complex of [(–L)Zr(OH)2]. 4,5 This polymer complex shows both exchange and addition reactions with anions, which can be applied to the selective adsorption of fluoride and the chromatographic separation of anions. 5,6 In this work, we studied whether such specificity of Zr(IV) could be utilized for potentiometric sensing of anions. A lipophilic derivative of IDA, N-dodecyliminodiacetic acid (H2dida), was adopted to introduce a Zr(IV) center in the membrane phase, and the performance of its Zr(IV) complex, Zr(dida)Cl2, was studied. Experimental Reagents A lipophilic chelating ligand of H2dida was synthesized by the controlled addition of NaOH to a mixture of dodecylamine with chloroacetic acid in an aqueous tetrahydrofuran solution. A crude precipitate obtained by acidification was recrystallized from a large volume of water. –1 indicated dimerization in a solid. This compound was not sufficiently soluble in any solvent, except for 1-butanol, which showed an appreciable solubility. A 1:1 complex, [Zr(dida)Cl2] (1), was prepared by the reaction of zirconium tetrachloride (230 mg, 1.0 mmol) and H2dida (300 mg, 1.0 mmol) in dehydrated 1-butanol under reflux for 40 h; the evolution of HCl gas was confirmed. IR absorption characteristic of the dimeric acid disappeared by complexation, and only two bands at 1630 and 1400 cm –1 remained. This complex could not be purified, because of the absence of a suitable solvent for recrystallization. Calcd. Measurement A polymeric membrane consisting of 1% ionophore, 66% o-NPOE, and 33% PVC by weight was subjected to the measurement. Another membrane, containing 30 mol% sodium tetraphenylborate (NaTPB) relative to the ionophore in addition to these three components, was also used to examine the effects of an additive salt. The electromotive force of the cell, Ag/AgCl | KCl(satd) || test solution | membrane | internal solution | Ag/AgCl, was measured at 25 ± 0.1˚C. The selectivity coefficients, with salicylate (Hsal –) as a primary species, were determined by a separate solution method at a fixed concentration of 10 –2 mol dm –3 at pH 2. With regard to anions involved in acid-base equilibria, an apparent coefficient against the total concentration (k′sal,X) as well as a …