There has been continuing growth in the number of PVC membrane electrodes that have been prepared for a variety of substances. These electrodes can be prepared by incorporating any of the many ion-exchanger or neutral-sequestering agents within a plasticized PVC matrix, and used as very useful tools for clinical, chemical and environmental analysis. 1 and Schiff-base complexes 6 have been reported as possessing improved characteristics in selectivity. Despite an urgent need for a triiodide-selective sensor for a direct determination of iodine or an indirect determination of some important specific oxidizing substances in many industrial, medical and environmental samples, there has been limited reports on a triiodide ion-selective electrode in the literature.
7,8We recently studied the electrochemical behavior and some chemical properties of various antifungal drugs containing piperazine or imidazole groups such as, ketoconazole in aqueous and non-aqueous media. [9][10][11][12] In this work, we initially studied the reaction between clotrimazole (CT) (a drug containing an imidazole ring) and triiodide ions. We found that the protonated clotrimazole (CTH + ) is precipitated in the presence of excess I3 -ions as a (CTH)I3 ion pair. Since the obtained ion pair is very stable and insoluble in aqueous solutions, we therefore employed this ion pair to prepare a new solvent polymeric membrane sensor for selective monitoring of the I3 -ion. Applications of the proposed membrane electrode as an indicator electrode in the potentiometric titration of triiodide ions in solutions and in the indirect potentiometric determination of CT from pharmaceutical preparations were investigated.
Experimental
Reagents and chemicalsReagent-grade benzyl acetate (BA), 2-nitrophenyl octyl ether (NPOE), nitrobenzene (NB), acetophenone (AP), bis(2-ethyl hexyl) sebacate (DOS), tetrahydrofuran (THF), chloroform and high relative molecular-weight PVC were purchased from Aldrich and used as received. Reagent-grade CT, oleic acid (OA), tetraphenyl phosphonium chloride (TPPC), iodine and all of the anionic salts used (all from Merck) were of the highest purity available, and were used without any further purification. Aqueous solutions were prepared by dissolving the appropriate salt or diluting standard solutions as specified in doubly distilled water.
ApparatusA WTW multilab 540 Ionalyzer (Germany) pH/mV meter was used for the potential and pH measurements at 25.0 ± 0.1˚C. The cell used was of the type Ag/AgCl, KCl (3 M) | internal solution KI3 (0.01 M) | PVC membrane | test solution | Ag/AgCl, KCl (3 M). The activities of anions were calculated using the Debye-Hückel procedure. 13 An LKB Model 4054 UV-Vis recording spectrophotometer with 10 mm quartz cells was used for absorbance measurements.
Preparation of ion-exchanger (CTH)I3To a 10 ml aliquot of a 0.01 M aqueous CT solution containing a few drops of HCl (1 M) was slowly added a triiodide solution (0.01 M) with continuous stirring until precipitation was completed. The resulting brown ion-pa...