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 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. [15][16][17][18][19][20][21][22][23][24][25][26] This paper describes for the first time the behavior and use of an electrode of the second kind, Pt|Hg|Hg 2 (Salic) 2 , the sensor of which was immobilized in graphite. This electrode works according to a principle which is quite different from that associated with previously described electrodes. The experimental variables that contribute to this electrode response, the calculation procedures utilized to determine the calibration curves jointly with the evaluation of this performance for the assay of aspirin in tablets (after hydrolysis of acetylsalicylate acid to salicylate), are described.
Experimental
Materials and solutionsDistilled, deionized water and "grade A" glassware were used throughout. All of the chemicals employed were of analytical reagent grade. Carbonate-free sodium hydroxide solutions were standardized potentiometrically with acid potassium phthalate, and then stored in polyethylene bottles protected with soda-lime tubes. The perchloric acid solutions were standardized potentiometrically with standard sodium hydroxide solutions. A sodium salicylate stock solution was standardized potentiometrically with a standard perchloric acid solution. Stock solutions of sodium perchlorate were analyzed by evaporating and drying to constant mass at 120˚C.Mercurous salicylate was prepared by mixing, in aqueous solution, the corresponding nitrate with an excess of sodium salicylate. The resulting precipitate was filtered through a sintered glass funnel, washed Química-UNESP, C. P. 355, 14801-970, ...
