New copper(II)-selective chemically modified carbon paste electrode based on etioporphyrin I dihydrobromide Yousry M. Issa ⇑ , Hosny Ibrahim, Ola R. Shehab Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt article info Article history: Received 26 April 2011 Received in revised form 16 November 2011 Accepted 18 November 2011 Available online 4 December 2011 Keywords: Copper Carbon paste Potentiometry Etioporphyrin abstract A new chemically modified carbon paste electrode (CMCPE) based on etioporphyrin I has been developed for the determination of Cu 2+ in real samples. The performance of this electrode was investigated using potentiometric measurements. The developed sensor exhibits a good linear response with a slope of 30.30 mV per decade over the concentration range of 1.28  10 6 –1.28  10 2 mol L 1 . It has a very low limit of detection, 8.99  10 7 mol L 1 , with response time of 5 s. The proposed electrode revealed very good selectivities with respect to alkali, alkaline earth and some transition metal ions and could be used in pH range of 4.5–8.5. The thermal stability of the electrode was studied. This modified electrode was successfully applied as an indicator electrode for potentiometric titration of Cu 2+ with EDTA and CDTA. Also the electrode was applied for direct determination of copper in different water samples, milk powder, brass powder and copper rod. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Copper is an essential element and is also toxic at high concen- tration, the maximum tolerable level for copper is 2.0 mg L 1 [1]. Copper deficiency results in anemia while its accumulation results in Wilson disease (WD) [2]. Potentiometric determination of cop- per assumes high importance in view of the widespread occur- rence of this element in the environment and the sophistications associated with the other instrumental techniques used for its determination. Reactivity and biological uptake of copper are strongly influenced by its free ion concentration. Potentiometric measurements with a copper selective electrode allow direct determination of free copper ion concentration in water samples [3–6]. For this reason researchers attempted to develop sensors for its determination at high selectivity and sensitivity. In spite of availability of a number of Cu(II) sensors, their use for Cu(II) estimation is limited, because they have shown interference by K + [7], Pb 2+ [8–12], Fe 3+ [13], Ni 2+ [14,15] and Co 2+ [16] ions, working over narrow concentration range [8,17–19], and show non-Nernstian response [8,9,18], limited pH range [20] and high response time [18]. In order to achieve wider applicability, these limitations need to be removed or neutralized. Efforts in this direc- tion are exerted to use different materials for preparing Cu 2+ sen- sors. The essential requirements to impart selectivity to the ion sensor are to use specific ion-recognition elements which show strong affinity for the assayed metal ion and give poor response for all others. Continuing efforts in this direction, we tested several carbon pastes of varying compositions based on different reagents specific for Cu(II). It was found that the CMCP based on etioporphy- rin I ligand is highly sensitive to Cu(II) over several alkali, alkaline earth, and transition metal ions. This work describes the prepara- tion, characterization and analytical applications of new Cu(II) ion-selective modified carbon paste electrode using etioporphyrin as ion-recognition element. 2. Experimental 2.1. Reagents and materials Sodium tetratphenylborate (NaTPB), sodium tetrakis (1-imidaz- olyl)borate (NaTImB), etiopophyrin I dihydrobromide 98.0%, potas- sium tetraphenylborate, o-nitrophenyloctyl ether (o-NPOE), dioctyl phthalate (DOP), dibutyl-butyl phosphonate (DBBP), tricre- syl phosphate (TCP), dioctyl adipate (DOA), and dioctyl sebacate (DOS) were purchased form Aldrich chemical company. Copper ni- trate trihydrate was purchased from Oxford laboratory products- Mumbai-India 95–103%. 2.2. Solutions Deionized water was used for all preparations and throughout all experiments. Stock solution of Copper nitrate trihydrate solu- tion (0.1 mol L 1 ) (Oxford product) was prepared by dissolving 2.415 g Cu(NO 3 ) 2 3H 2 O in 100 ml deionized water, and nitric acid 1572-6657/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jelechem.2011.11.024 ⇑ Corresponding author. Tel.: +20 2 35676559; fax: +20 35728843. E-mail address: yousrymi@yahoo.com (Y.M. Issa). Journal of Electroanalytical Chemistry 666 (2012) 11–18 Contents lists available at SciVerse ScienceDirect Journal of Electroanalytical Chemistry journal homepage: www.elsevier.com/locate/jelechem