Available online at www.sciencedirect.com Talanta 74 (2007) 125–131 Novel potentiometric membrane sensor based on 6-(4-nitrophenyl)-2-phenyl-4,4-dipropyl-3,5-diaza-bicyclo[3,1,0] hex-2-ene for detection of strontium (II) ions at trace levels M.A. Zanjanchi ∗ , M. Arvand, A. Islamnezhad, N.O. Mahmoodi Department of Chemistry, Faculty of Science, University of Guilan, P.O. Box 1914, Rasht, Iran Received 28 February 2007; received in revised form 17 May 2007; accepted 20 May 2007 Available online 26 May 2007 Abstract A new PVC membrane strontium ion-selective electrode has been constructed using 6-(4-nitrophenyl)-2-phenyl-4,4-dipropyl-3,5-diaza- bicyclo[3,1,0] hex-2-ene (NPDBH) as a neutral ionophore. The electrode was prepared with 7% NPDBH (as ionophore), 57% acetophenone (as plasticizer), 30% PVC and 6% oleic acid (as lipophilic additive). The electrode responds to Sr 2+ ion with a sensitivity of 28.2 ± 0.5 mV/decade over the range 1.0 × 10 -6 –1.0 × 10 -1 mol L -1 and in a pH range of 3.0–10.0. The limit of detection was 2.4 × 10 -7 mol L -1 . It has a response time of <20s and can be used for at least three months without any divergence in potentials. The proposed electrode shows good discrimination of Sr 2+ ion from several cations. The effect of organic solvents on electrode response was examined. The results show that this electrode can be used in ethanol media up to 15% (v/v) concentration without interference. The isothermal temperature coefficient of this electrode amounted to 0.00019 V/ ◦ C. The electrode was found to work well under laboratory conditions. It was successfully applied to the determination of strontium ions in human urine and bone digests. © 2007 Published by Elsevier B.V. Keywords: Strontium; Sr 2+ -selective electrode; PVC membrane; Neutral carrier; ISEs; Isothermal temperature coefficient 1. Introduction Ion-selective electrodes (ISEs) have been known for the past three decades. They are well established in the most frequent routine application in the fields of environmental, agricultural, industrial and clinical analysis. This is due to their several advan- tages, such as speed, ease of preparation, simple instrumentation, relatively fast response, wide dynamic range, selectivity and low cost. ISEs are also appropriate for on-site monitoring. There- fore, the analysis by ISEs is a preferred procedure for those ions for which selective electrodes are available. That is the reason why researchers in the field of ISEs attempt to prepare highly selective electrodes for trace determination of the species. The capabilities of ion-selective electrodes have been changed dra- matically in recent years so that the lower limit of detection of ISEs has improved by a factor of up to one million and the discrimination factor of interferences from ions by up to one ∗ Corresponding author. Tel.: +98 131 3226643; fax: +98 131 3220066. E-mail address: zanjanchi@guilan.ac.ir (M.A. Zanjanchi). billion [1]. Unlike most other advances in trace determination, this has not been achieved by significant changes in instrumen- tation, but instead by the development of new materials [2]. Therefore, it is expected that the range of application of ISEs will increase in the near future coinciding with devising new materials. Strontium belongs to the alkaline earth elements of group 2A of the periodic table and ranks fifteenth in abundance among the elements. It is widely distributed in the environment, soils, plants and humans tissues. It is used in a variety of optical mate- rials, paints, plastics, bricks, tiles and ferrite magnets. It is used in pyrotechnics and signaling devices due to its brilliant red color formation. The determination of strontium, therefore, is important and common instrumental methods such as induc- tively coupled plasma(ICP)-AES [3,4] and atomic absorption spectroscopy [5,6] can be used for its measurement. However, these methods are time consuming and are not suitable for large scale monitoring because of high cost and tedious requirement of sample preparation. In these circumstances, a convenient potentiometric determination by ion-selective electrode is bene- ficial. 0039-9140/$ – see front matter © 2007 Published by Elsevier B.V. doi:10.1016/j.talanta.2007.05.034