ACETYLSALICYLIC-ACID DETERMINATION IN PHARMACEUTICAL SAMPLES BY FIA-POTENTIOMETRY USING A SALICYLATE-SENSITIVE TUBULAR ELECTRODE WITH AN ETHYLENE-VINYL ACETATE MEMBRANE

The construction of a salicylate-sensitive tubular potentiometric elec trode for flow injection analysis (FIA) is described, in which an ethy lene-vinyl acetate (EVA) copolymeric membrane, 40% in vinyl acetate, i s applied directly onto a conducting support consisting of a mixture o f an epoxy resin and graphite. The tubular salicylate ion-selective el ectrode is based on tricaprylyl-trimethyl-ammonium (Aliquat(TM)) salic ylate as the ion-exchanger, supported on the polymeric matrix without plasticizer solvent. The tubular electrode showed a response of 58.3 m V per concentration decade within the 5.0x10(-3)-5.0x10(-1) mol l(-1) salicylate range in 0.1 mol l(-1) Tris-HCl buffer (pH=7.5). Iodide is the main analytical interferent; the electrode response time was 5 s a t 25 degrees C. Determinations of acetylsalicylic acid in tablet sampl es by the proposed method exhibit relative errors lower than 2%, when compared with a spectrophotometric method. The useful lifetime of the tubular sensor is longer than 3 months. (C) 1998 Elsevier Science B.V.