Talanta 71 (2007) 186–191 Determination of nitrate in mineral water and sausage samples by using a renewable in situ copper modified electrode Thiago R.L.C. Paix˜ ao a , Juliana L. Cardoso b , Mauro Bertotti a,∗ a Instituto de Qu´ ımica, Universidade de S˜ ao Paulo, S˜ ao Paulo 05508-900, SP, Brazil b Escola Polit´ ecnica, Universidade de S˜ ao Paulo, S˜ ao Paulo, SP, Brazil Received 23 January 2006; received in revised form 21 March 2006; accepted 22 March 2006 Available online 9 May 2006 Abstract A new approach for in situ electrodeposition of a renewable copper layer onto a copper electrode is reported. The active surface was obtained by anodic dissolution of a copper electrode at an appropriate potential and further redeposition of copper ions still remaining at the diffusion layer. Under optimal experimental conditions the peak current response increases linearly with nitrate concentration over a range of 0.1–2.5 mmol L -1 . The repeatability of measurements for nitrate was evaluated as 1.8% (N = 15) and the limit of detection of the method was found to be 11 mol L -1 (S/N = 3). Nitrate contents in two different samples (mineral water and sausages) compared well with those obtained from using the standard Griess protocol at a 95% of confidence level measured by the t-student test. The interference from chloride on the nitrate analysis and the possibility of simultaneous determination of nitrite were also examined. © 2006 Elsevier B.V. All rights reserved. Keywords: Nitrate; Freshly copper layer; Mineral water and sausage 1. Introduction Nitrates have a large distribution on the nature. In food, nitrates are used for conservation of meat and in the agricul- ture its use as a fertilizer is widespread. However, there are concerns on contamination of water supplies [1] and a corre- lation between cancer in stomach and nitrate levels in potable water in UK has been suggested [2]. Similar studies were carried out in Italy [3] and authors have also found a strong correla- tion between high cancer levels and nitrate concentration above 4.5 mg L -1 . Toxicological problems associated with nitrates and nitrites are related to the formation of endogenously N-nitrous compounds (nitrosamines and nitrosamides), the carcinogenic activity of these species being well-known [3]. Hence, measure- ments of nitrate levels in potable water and other products that have a high consumption by humans, like conserving food, are increasingly relevant. A review in literature [4] shows a large number of methods for the quantification of nitrate and most of them are based on ∗ Corresponding author. Tel.: +55 11 3091 3837; fax: +55 11 3815 5579. E-mail address: mbertott@iq.usp.br (M. Bertotti). techniques such as spectrophotometry, electrochemistry or chro- matography (liquid chromatography or capillary electrophore- sis). It should be pointed out, additionally, that the majority of the procedures depend on a previous step involving the stoi- chiometric conversion of nitrate to nitrite by using convenient chemical reductors such as Cu/Cd. The large number of studies in the electroanalytical field on the determination of nitrate can be classified in two main groups, voltammetric/amperometric or potentiometric methods. The lat- ter one involves the use of ion-selective electrodes, which are based on the selective passage of the analyte from the solution to another phase, the potential gradient being proportional to the concentration. Accordingly, the use of ion-selective electrodes is widespread for the analysis of nitrate [5–10] and several other anions [11–15]. On the other hand, voltammetric/amperometric techniques depend on the electrochemical reduction of nitrate at electrodic surfaces and different materials have been used such as copper [16–23], cadmium [17,24,25], lead [26,27], sil- ver [22,28] and boron-doped diamond [29–31]. However, the use of bare unmodified electrodes for the direct determination of nitrate is difficult owing to the slow kinetics of the charge trans- fer [32], methods based on the direct reduction of nitrate being characterised by low sensitivity and irreproducibility and asso- 0039-9140/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2006.03.040