Novel Validated Potentiometric Methods for the Determination of Torasemide in Bulk Drug, in Formulations and in Plasma

Three novel techniques for the selective determination of torasemide (TOS) in bulk powder, in formulations and in plasma were described. The three techniques were the construction and electrochemical response characteristics of novel poly (vinyl chloride) matrix membrane sensors for torasemide cation based on the use of the ion-association complexes of this cation with tetraphenyl borate, phosphotungestic acid and ammonium reineckate counter anions as ion exchange sites in a plasticized PVC matrix, either as ion selective membranes, microcoated wire or as microsized graphite selective sensors. All these sensors were prepared and fully characterized in terms of composition, life span, usable pH range, response time and temperature. The electrodes were selectively applied for the potentiometric determination of torasemide in pure form, pharmaceutical preparations and in plasma. These sensors showed near Nernstian responses with slopes of 28.3, 28.9, 27.9, 28.0, 30.0, 27.7, 28.5, 29.2 and 27.5 mv over the concentration ranges of 1.0×10-6-1.0×10- M for all sensors. The electrodes exhibit good selectivity for (TOS) with respect to a large number of inorganic cations, organic cations, sugars and amino acids. The proposed electrodes offer the advantages of simplicity, accuracy and applicability to turbid and colored samples. The behavior of the three sensors in presence of human plasma was also studied and reasonable results were obtained. All the fabricated sensors were validated according to the International Conference on Harmonization (ICH) guidelines and successfully applied for the determination of the studied drug in pure form, pharmaceutical preparations and in plasma without any interference.