Analytical Sciences

An Electrode of the Second Kind for AspirinDetermination in Tablet Formulations

Vinicius J. F. FERREIRA, Ana C. V. CAVALHEIRO, Enelton FAGNANI, Mercedes de MORAES, Leonardo PEZZA* , Helena R. PEZZA and Cristo B. MELIOS

Instituto deQuimica-UNESP, C. P. 355, 14801-970, Araraquara, SP, Brazil

This paper describes the construction of anelectrode of the second kind,Pt|Hg|Hg₂(Salic)₂|Graphite, sensitive to salicylate. This electrode responds to the salicylate ion with a sensivity of 58.66mV/decade over the range 6.0x10^-4 - 1.0x10^-1 mol/l atpH 6.0 and an ionic strength of 0.500 - 3.00 mol/l, adjusted withNaClO₄. The electrode is easily constructed, shows a fastresponse time, is low in cost, has excellent response stability, and has alifetime greater than 18 months, which is much longer than those reportedearlier for other systems. The influence of 10 different carboxylate andinorganic anions on the electrode response showed that there was negligibleinterference by most of these ions. It was used to determine aspirin intablets (after hydrolysis of acetylsalicylic acid to salicylate) by meansof the standard additions method. The results obtained using this electrodefor aspirin determination, in three different samples of antithermic drugs,compared favorably with the results given by the British Pharmacopoeiamethod. (Keywords: Salicylate sensitive electrode, mercury-mercuroussalicylate, pharmaceutical analysis, salicylate and acetyl-salicylic aciddetermination)

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