An Electrode of the Second Kind for Aspirin Determination in Tablet Formulations
Salicylate and its analogues, such as acetylsalicylate (aspirin) are commonly used as with effective analgesics, and are available to the public in a wide variety of formulations. Aspirin, a prostaglandin biosynthesis inhibitor, is also an important antipyretic drug. Recently, a new therapeutic use has emerged based on its unique antiplatelet aggregation property, so that aspirin is now being widely used to treat cardiovascular complications. 1 Although gas and liquid chromatographic methods
... ographic methods are the most specific methods for salicylate 2,3 , but their general availability, especially for emergency use, is limited and probably not necessary. 4,5 Official methods, namely those proposed by the British Pharmacopoeia 6 , are usually based on time-consuming and tedious titrimetric procedures, which in themselves, justify the search for speedier methods. Direct potentiometric methods, however, are simpler and faster. In this context, the construction and analytical applications of electrodes that are sensitive to salicylate ion have been described. Most salicylate ion-sensitive electrodes use a liquid sensor immobilized in a porous membrane of Orion electrode series 92-20. 7-14 This fact restringes its utilization due to manipulation difficulty and the mechanical deficiency of this kind of setting up. With the evolution of ion-selective electrodes, in its brief history and development, other kinds of salicylate ion-sensitive electrodes has been described in the literature.             This paper describes for the first time the behavior 249 ANALYTICAL SCIENCES MARCH 1999, VOL. 15 1999 This paper describes the construction of an electrode of the second kind, Pt|Hg|Hg2(Salic)2|Graphite, sensitive to salicylate. This electrode responds to the salicylate ion with a sensivity of 58.66 mV/decade over the range 6.0×10 −4 -1.0×10 −1 mol/l at pH 6.0 and an ionic strength of 0.500 -3.00 mol/l, adjusted with NaClO4. The electrode is easily constructed, shows a fast response time, is low in cost, has excellent response stability, and has a lifetime greater than 18 months, which is much longer than those reported earlier for other systems. The influence of 10 different carboxylate and inorganic anions on the electrode response showed that there was negligible interference by most of these ions. It was used to determine aspirin in tablets (after hydrolysis of acetylsalicylic acid to salicylate) by means of the standard additions method. The results obtained using this electrode for aspirin determination, in three different samples of antithermic drugs, compared favorably with the results given by the British Pharmacopoeia method.