As características, o desempenho e a aplicação de um eletrodo do tipo Pt⎪Hg⎪Hg 2 (NAP) 2 ⎪ Graphite, onde NAP=íon naproxenato, são descritas. O eletrodo responde a NAP com sensibilidade de (58,1± 0,9) mV década -1 no intervalo de 5,0 × 10 -5 -1,0 × 10 -2 mol L -1 , a pH 6,0-9,0 e com um limite de detecção de 3,9 × 10 -5 mol L -1 . O eletrodo é de baixo custo e facilmente construído, apresenta um rápido tempo de resposta (10-35 s) e pode ser usado por um período de seis meses sem qualquer divergência considerável nos potenciais. O sensor supracitado mostrou boa seletividade para naproxeno na presença de várias substâncias, tais como carboxilatos e ânions inorgânicos, sendo aplicado na análise direta de naproxeno em medicamentos (comprimidos) via método da adição de padrão. Os resultados analíticos obtidos com o eletrodo proposto estão em boa concordância com aqueles obtidos pelo procedimento preconizado na Farmacopéia Americana.The characteristics, performance, and application of an electrode, namely, Pt⎪Hg⎪Hg 2 (NAP) 2 ⎪ Graphite, where NAP stands for naproxenate ion, are described. This electrode responds to NAP with sensivity of (58.1± 0.9) mV decade -1 over the range 5.0 × 10 -5 -1.0 × 10 -2 mol L -1 at pH 6.0-9.0 and a detection limit of 3.9 × 10 -5 mol L -1 . The electrode is easily constructed at a relatively low cost with fast response time (within 10-35 s) and can be used for a period of 6 months without any considerable divergence in potentials. The proposed sensor displayed good selectivity for naproxen in the presence of several substances, especially concerning carboxylate and inorganic anions. It was used for the direct assay of naproxen in commercial tablets by means of the standard additions method. The analytical results obtained by using this electrode are in good agreement with those given by the United States Pharmacopeia procedure.Keywords: naproxenate-sensitive electrode, potentiometry, pharmaceutical formulations Introduction Naproxen [(+)-2-(6-metoxy-2naphthyl)propionic acid], is a non-steroidal anti-inflammatory drug that also presents analgesic and antipyretic properties often preferred to acetylsalicylic acid because of its better absortion following oral administration and fewer adverse effects.Naproxen is extensively used in the treatment of many diseases like rheumatoid arthrits, degenerative joint disease, ankylosing spondylits, acute gout and primary dismenorrea. 1 Like other non-steroidal anti-inflammatory drugs, it inhibits the biosyntesis of prostaglandins. 1 The United States Pharmacopeia 2 2003 reports an highperformance liquid chromatography (HPLC) method for the determination of naproxen tablets. Several analytical methods have been reported for the determination of naproxen in pharmaceutical preparations including UV-visible spectrophotomery, 3-5 spectrofluorimetry, 6-8 room temperature phosphorimetry, 9,10 voltametry, 11 high-performance liquid chromatography, 12-14 capillary electrophoresis, 15,16 coulometry 17 and oscilometric titration. 18 However, most of these techniq...