DIPHENHYDRAMINE-SELECTIVE PLASTIC MEMBRANE SENSOR AND ITS PHARMACEUTICAL APPLICATIONS

Different types of PVC-matrix ion-selective electrodes (ISEs) that res pond to the cationic form of diphenhydramine (Dph) are described. Thre e ion-pairing agents, namely tetraphenylborate (TPB), phosphotungstate (PT), reineckate (RN) are investigated. The best PVC polymeric membra ne contains Dph-TPB as active material. The electrode, based on the io n-pair complex with TPB anion shows near-Nemstian response in the conc entration range 10(-2) to 3.5 x 10(-5) M (Dph.HCl). Changing pH within the range 2.0-7.5 did not affect the electrode performance. The stand ard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the electrode (0.0015 6 V/degrees C) The electrode showed a good selectivity for Dph with re spect to a large number of inorganic and organic cations. The standard addition method and potentiometric titration were applied to determin e Dph amounts in pharmaceutical preparations. The Dph selective membra ne electrode was also applied to the determination of the dissolution profile of Dph tablets. The dissolution results were compared with spe ctrophotometrically determined ones.