N,N′-Bis(3-methyl-1-phenyl-4-benzylidine-5-pyrazolone)propylenediamine Schiff base as a neutral carrier for silver (I) ion-selective electrodes

New highly selective silver (I) electrodes were prepared by incorporating N,N′-bis(3-methyl-1-phenyl-4-benzylidine-5-pyrazolone)propylenediamine (I2) as a neutral ionophore into plasticized PVC membranes. The best response characteristics were obtained using the composition—I2:KTpClPB:PVC:DBP in the percentage ratio of 4:1.5:60:120 (w:w). The electrodes exhibit a linear response with a near Nernstian slope of 59.3 mV/decade within the silver ion concentration range of 10−6–0.1 mol L−1, with a working pH range (4–10). The electrodes possessed a fast response time of 30 s for low concentration (10−6 mol L−1) and 5 s for higher concentration (10−5–0.1 mol L−1). The electrodes showed excellent selectivity towards Ag+ ion over a wide range of alkali, alkaline earth, and transition metals ions. The electrodes displayed a very good selectivity for silver ion against the serious interferents Hg2+ and Cu2+ ions, which is a valuable property of these electrodes. The high selectivity arises from the strong complexation of I2 with Ag+ compared with other ions as determined by the sandwich membrane method. Density Functional Theory calculations performed using the Gaussian 03 program indicate a tetradentate coordination of the metal ion by I2. Calculated binding energies for different metal ions also support high selectivity for silver (I) ion. These electrodes were successfully used in the potentiometric titration of halides with silver ion and in the determination of silver in radiology films.