Journal of Pharmaceutical and Biomedical Analysis 34 (2004) 871–878 Effects of EDTA on signal stability during electrochemical detection of acetaminophen Rosangela M. de Carvalho, Renato S. Freire 1 , Susanne Rath, Lauro T. Kubota ∗ Instituto de Qu´ ımica, UNICAMP, CP 6154, 13083-970 Campinas, SP, Brazil Received 1 July 2003; received in revised form 24 October 2003; accepted 25 November 2003 Abstract The use of EDTA in the medium to avoid the passivation of a solid electrode during electrochemical analysis of acetaminophen is presented in this work. The performance of this system was investigated with respect to pH, applied potential and supporting electrolyte concentration. The major advantage in using EDTA in the supporting electrolyte is the significant increase in sensitivity, precision and stability of the measurements, when compared to the system in absence of the chelating agent. The sensitivity increases 5.5 times (21.5 and 3.9 mA l mol -1 in the presence and the absence of EDTA, respectively), the repeatability (n = 20) is 3.5 times better, expressed by within-run-precision of 4.0% for 6.0 × 10 -5 mol l -1 acetaminophen in the presence of EDTA while, in its absence, the within-run-precision was higher than 14%. Moreover, the system showed excellent stability, allowing more than 120 measurements with no significant changes. © 2003 Elsevier B.V. All rights reserved. Keywords: EDTA; Acetaminophen; Solid electrodes; Electroanalytical; High performance method 1. Introduction Acetaminophen (paracetamol or N-acetyl-p-amino- phenol) is a common over-the-counter drug that is present in many medications, without the secondary effects of the salicylates on the gastric mucose, al- though it may cause liver damage in some instances [1]. Acetaminophen (AC) is an effective and safe anal- ∗ Corresponding author. Tel.: +55-1937883127; fax: +55-1937883023. E-mail address: kubota@iqm.unicamp.br (L.T. Kubota). 1 Present address: Instituto de Qu´ ımica, Universidade de São Paulo-USP, CEP 05513-970 São Paulo, SP, Brazil. gesic agent used worldwide for the relief of mild to moderate pain associated with headache, backache, arthritis and postoperative pain. It is also used for re- duction of fevers of bacterial or viral origin [2,3]. Several analytical methods have been proposed for the determination of acetaminophen: spectrophoto- metric [2–6], spectrofluorimetric [7], reversed-phase HPLC [8–13], ion-pairing HPLC [12], capillary electrophoresis [13] and electrochemical [4,14,15] as well as in flow-injection analysis (FIA) coupled to various detection systems [15]. Although simple UV-spectrometric methods are frequently employed, the direct determination of analytes based on in- trinsic absorbance measurements in the UV region 0731-7085/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.jpba.2003.11.005