Bismuth Modified Disposable Pencil-Lead Electrode for Simultaneous Determination of 2-Nitrophenol and 4-Nitrophenol by Net Analyte Signal Standard Addition Method Karim Asadpour-Zeynali,* Parvaneh Najafi-Marandi Department of Analytical Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz 5166616471, Iran tel. + 98 411 3393113, fax: + 98 411 3340191 *e-mail: asadpour@tabrizu.ac.ir; k.zeynali@gmail.com Received: February 23, 2011; & Accepted: April 30, 2011 Abstract A pencil-lead electrode modified with a thin film of bismuth, that is “environmental friendlier” than mercury, was used for electrocatalytic reduction of 2-nitrophenol (2-NP) and 4-nitrophenol (4-NP) by differential pulse voltam- metry and net analyte signal standard addition method (NASSAM). The modified electrode has electrocatalytic be- havior toward reduction of 2-NP and 4-NP. Because of similar structures of analytes, at the modified electrode they have high overlapped signals that determination of them in the presence of each other is impossible with univariate methods. NASSAM is a very recently introduced method that is a new modification of the standard addition method, which was used for the simultaneous determination of 2-NP and 4-NP. Keywords: Nitrophenol, Net analyte signal standard addition method, Bismuth modified electrode DOI: 10.1002/elan.201100103 1 Introduction Nitrophenols (NPs) are organic compounds which are used in industrial, agricultural and defense applications. They are used as intermediates in the manufacture of pharmaceuticals, pesticides, pigments, explosives, dyes, rubber chemicals etc. [1]. They are produced by microbial hydrolysis of several organophosphorous pesticides, such as parathion [2,3] or by photodegradation of pesticides that contain the nitrophenol moiety [4]. Nitrophenols also result from natural processes in the biosphere and are now common pollutants in several ecosystems in de- veloped countries [5]. The compounds o-nitrophenol, p- nitrophenol and 2,4-dinitrophenol are listed on the Priori- ty Pollutants List. Therefore, the monitoring of them is essential for environmental pollution control [6]. At pres- ent, flow-injection analysis, spectrophotometric method, high performance liquid chromatography and capillary electrophoresis have been widely used for this purpose. However, for the majority of these methods, some sample pretreatment involving separation, extraction and adsorp- tion is generally necessary. These can be time-consuming and complex [7–9]. Electrochemical methods have also been applied for the determination of NP isomers [10–13]. These methods, such as differential pulse polarography (DPP) offer high sensitivity, low limit of determination, easy operation, and sometimes the use of simple instrumentation. The use of classical polarography has been reported for the analysis of nitro group-containing compounds in some samples, such as blood extracts and industrial waste water [14]. Furthermore, DPP was employed for the determination of trace amounts of various compounds, such as nitroben- zene and 4-nitrophenol. But few reports concerned simultaneous determination of these isomers by application of chemometrics method [15]. Because isomeric compounds such as nitrophenoles have similar properties and interfere with each other and often coexist in one product, so there are growing de- mands for simultaneous determination of these materials. Modified electrodes are being used frequently in the voltammetric determination of organic compounds be- cause of their efficiency and the selectivity that can be obtained varying the modifier, one of them is bismuth modified electrodes, as an appropriate alternative to mer- cury electrodes. Mercury electrodes (MEs) and mercury- film electrodes (MFEs) provide valuable tools for electro- analysis in the reductive potential region. The greatest drawback of them, which is effective on our environment, is the extreme toxicity of mercury and the mercury salts employed for the preparation of MEs. As a result, elec- trode materials that can potentially replace mercury are continually sought. In 2000, a new type of electrode, the bismuth film electrode (BFE), was proposed as an alter- native to MFEs [16]. BFEs are prepared by plating a thin bismuth, rather than mercury, as a film on a suitable sub- strate material [16–20]. Electroanalysis 2011, 23, No. 9, 2241 – 2247 # 2011 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim 2241 Full Paper