Available online at www.sciencedirect.com Journal of Hazardous Materials 157 (2008) 18–24 A fast response hafnium selective polymeric membrane electrode based on N,N ′ -bis(-methyl-salicylidene)-dipropylenetriamine as a neutral carrier B. Rezaei ∗ , S. Meghdadi, R. Fazel Zarandi Department of Chemistry, Isfahan University of Technology, Isfahan 84156-83111, Iran Received 16 September 2007; received in revised form 18 December 2007; accepted 19 December 2007 Available online 26 December 2007 Abstract In this study a new hafnium selective sensor was fabricated from polyvinylchloride (PVC) matrix membrane containing neutral carrier N,N ′ -bis(- methyl-salicylidene)-dipropylenetriamine (Mesaldpt) as a new ionophore, sodium tetraphenyl borate (NaTPB) as anionic discriminator and dioctyl phthalate (DOP) as plasticizing solvent mediator in tetrahydrofuran solvent. The electrode exhibits Nernstian response for Hf 4+ (Hafnium(IV)) over a wide concentration range (2.0 × 10 -7 to 1.0 × 10 -1 M) with the determination coefficient of 0.9966 and slope of 15.1 ± 0.1 mV decades -1 . The limit of detection is 1.9 × 10 -7 M. The electrode has a fast response time of 18 s and a working pH range of 4–8. The proposed membrane shows excellent discriminating ability towards Hf 4+ ion with regard to several alkali, alkaline earth transition and heavy metal ions. It can be used over a period of 1.5 months with good reproducibility. It is successfully applied for direct determination of Hf 4+ in solutions by standard addition method for real sample analysis. © 2008 Elsevier B.V. All rights reserved. Keywords: Hafnium selective sensor; Polyvinylchloride membrane; Potentiometry; Polyvinylchloride 1. Introduction The utility of ion sensors in the fields of environmental, agri- cultural and medicinal analysis is being increasingly realized regard to the rapid growth of industry and technology [1]. The most attractive and interesting aspects of this technique are the speed with which samples can be analyzed, accuracy, repro- ducibility, selectivity, portability of the device, non-destruction of the sample and cost effectiveness of the commercial sen- sors [2]. Polymeric carrier-based ion-selective electrodes (ISEs) for determination of the alkali metal cations such as sodium, potassium and lithium [3–9] have been studied numerously. The efforts are required to develop ion-selective electrodes for heavy metal ions in very low concentrations [10–13]. Hafnium is a strategic element. Its thermal neutron absorption cross sec- tion is nearly 600 times that of zirconium and because of its ability to absorb neutrons it is used to make control rods for ∗ Corresponding author. Tel.: +98 311 3913268; fax: +98 311 3912350. E-mail address: rezaei@cc.iut.ac.ir (B. Rezaei). nuclear reactors. It also has excellent mechanical properties and exceptional corrosion–resistance properties. However due to the similarity of behavior of hafnium and zirconium its determina- tion is difficult. The other principal uses of hafnium, as a heavy metal, are in nickel-based super alloys, nozzles for plasma arc metal cutting, and high-temperature ceramics [14]. So its deter- mination is important. Also all hafnium compounds should be regarded as toxic although initial evidence would appear to suggest that the danger is limited but the metal dust presents a fire and explosion hazard. Overexposure to hafnium and its compounds could cause mild irritation of the eyes, skin, and mucous membranes [15]. Due to vital importance of hafnium determination in chemical, clinical and industrial analysis, many voltametric, conductometric, chromatographic and spectromet- ric techniques have been reported in the literatures [16–21], but most of them are sophisticated and suffer from the lack of reproducibility, so we were interested in preparation of a new solvent polymeric membrane electrode for selective monitor- ing of hafnium ion in solutions. In the present work, Mesaldpt that has been synthesized recently in our laboratories [22] was used as an excellent neutral ion carrier for construction of 0304-3894/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2007.12.070