www.elsevier.nl/locate/jelechem Journal of Electroanalytical Chemistry 481 (2000) 34 – 41 Development of a new FIA-potentiometric sensor for dopamine based on EVA-copper(II) ions L. Rover Ju ´ nior a,1 , J.C.B. Fernandes a , G. de Oliveira Neto b , L.T. Kubota a, * a Instituto de Quı ´mica -UNICAMP, PO Box 6154, 13083 -970 Campinas, SP, Brazil b Faculdade de Cie ˆncias Farmace ˆuticas -USF, 12900 -000 Braganc ¸a Paulista, SP, Brazil Received 16 July 1999; received in revised form 15 November 1999; accepted 22 November 1999 Abstract A flow injection analysis (FIA) system using a tubular electrode based on the redox properties of copper(II) ions immobilized in a poly(ethylene-co -vinyl acetate) (EVA) membrane was developed for dopamine determination. The Cu 2 + was trapped in the EVA (40% m/m) matrix and dispersed on the surface of a graphite-epoxy flow-through electrode. The electrode based on the dopamine oxidation catalyzed by Cu 2 + exhibited a near-Nernstian response (83.2 0.2 mV decade -1 ) for dopamine concentra- tion between 1.0 ×10 -3 and 1.0 ×10 -2 mol l -1 (r =0.9992), employing 0.25 mol l -1 KH 2 PO 4 buffer, containing 0.1 mol l -1 H 2 O 2 at pH 7.0, as a carrier solution. The potentiometric-FIA system allows an analytical frequency of about 25 samples per hour with a good precision (variance lower than 4.2%). The best potentiometric response was achieved using an EVA membrane containing 5.0% (m/m) Cu 2 + ions. The use of hydrogen peroxide in a flow-system makes an efficient reoxidation of the Cu 1 + ions possible in the EVA membrane. The relative standard deviation for dopamine determination in pharmaceutical samples, without any previous treatment, was about 4.7%. The useful lifetime for the dopamine sensor was longer than 3 months, in continuous use. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Potentiometric sensor; Copper(II); EVA membrane; Dopamine determination; FIA 1. Introduction Catecholamine drugs are aromatic vicinal-diols that consist of amines attached to a benzene ring bearing two hydroxyl groups (catechol). The catecholamines are primarily synthesized in vesicles of the chromaffin cells in the adrenal medulla. These drugs are widely used in the treatment of bronchial asthma, hypertension, Parkinson’s disease, drug abuse, schizophrenia and myocardial infarction. Dopamine, a neurotransmitter, is one of the naturally occurring catecholamines and its hydrochloride salt has been used in the correction of acute congestive and renal failures associated with shock episodes [1 – 4]. The catecholamines are present in relatively large amounts in drugs and many efforts have been made to develop rapid, simple and accurate analytical proce- dures for their determination. Several methods have been described in the literature for dopamine determi- nation in biological samples and pharmaceutical formu- lations like spectrophotometry [5 – 8], gas [9,10] and liquid [11,12] chromatography and amperometry [13 – 16]. The major part of the sensors for dopamine deter- mination developed up until now are based on am- perometric techniques coupled with or without chro- matographic methods. Recent papers [17,18] have de- scribed the catalytic detection of dopamine in a flow-injection system based on a packed bed reactor containing tyrosinase and a highly sensitive ampero- metric sensor for catecholamine determinations. The dopamine instability in aqueous solutions becomes difficult, its determination depending on the tempera- ture, ultraviolet light, oxygen pressure, pH and some catalysts, such as copper(II) ions [19 – 21]. * Corresponding author. Tel.: +55-19-7883127; fax: +55-19- 7883023. E-mail address: kubota@iqm.unicamp.br (L.T. Kubota) 1 Present address: Faculdade de Cie ˆncias Me ´dicas-UNICAMP, PO Box 6111, 13083-970, Campinas, SP, Brazil. 0022-0728/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved. PII:S0022-0728(99)00474-X