Analytica Chimica Acta 681 (2010) 27–32 Contents lists available at ScienceDirect Analytica Chimica Acta journal homepage: www.elsevier.com/locate/aca A novel ion selective sensor for promethium determination Vinod K. Gupta a,b,∗ , Rajeev Jain c , A.J. Hamdan b , Shilpi Agarwal c , Arvind K. Bharti a a Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247 667, India b Chemistry Department, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia c School of Studies in Chemistry, Jiwaji University, Gwalior 474011, India article info Article history: Received 21 July 2010 Received in revised form 21 September 2010 Accepted 22 September 2010 Available online 1 October 2010 Keywords: Ion selective sensor Promethium Schiff base Poly(vinyl chloride) membranes abstract This is a first promethium 145 ion-selective sensor based on the comparative study of two Schiff base ligands (X 1 and X 2 ) as neutral ionophores. Effect of various plasticizers: 2-nitrophenyloctylether (o-NPOE), dibutyl phosphonate (DBP), dioctylphthalate (DOP), tri-(2-ethylhexyl) phosphate (TEHP), dibutyl butylphosphonate (DBBP), chloronaphthalene (CN) and anion excluders: potassium tetrakis (p-chloropheny1) borate (KTpClPB), sodiumtetraphenylborate (NaTPB) and oleic acid (OA) have been studied. The membrane with a composition of ionophore (X 1 /X 2 ):KTpClPB:PVC:o-NPOE (w/w, %) in the ratio of 5:5:30:60 exhibited best performance. The best responsive membrane sensors (8 and 21) exhib- ited working concentration range of 4.5 × 10 -7 –1.0 × 10 -2 M and 3.5 × 10 -6 –1.0 × 10 -2 M with a detection limits of 3.2 × 10 -7 M and 2.3 × 10 -6 M and Nernstian slopes of 20.0 ± 0.5, 19.5 ± 0.5 mV decade -1 of activ- ity, respectively. The sensor no. 8 works satisfactorily in partially non-aqueous media up to 10% (v/v) content of methanol, ethanol and acetonitrile. Analytical application of the proposed sensor has been demonstrated in determination of promethium (III) ions in spiked water samples. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Promethium is a highly radioactive lanthanide and a synthetic rare earth metal. Promethium-145 is the most common radioac- tive isotope with a half life time of 17.7 years. Promethium is a normal by-product of the nuclear fission of uranium-238 and the radioactive decay of europium-151. It can also be synthesized by bombarding the more common lanthanide metal neodymium with neutron radiation, or by ion-exchange technology. Promethium (III) trichloride mixed with zinc sulphide was used as a major lumi- nous paint for watches. This mixture is still occasionally used for some luminous paint applications. It is used in nuclear battery [1] in which cells convert the beta emissions into electric current. It has possible future applications in portable X-ray sources, and as auxiliary heat or power sources for space probes and satellites. High performance liquid chromatography [2] and liquid scin- tillation counting techniques [3] are limited methods for the determination of promethium in real samples. Therefore, a need was felt for the development of a rapid and sensitive method for the determination of promethium. The Schiff base compounds have recently attracted attention in the field of ion selective sensors due ∗ Corresponding author at: Department of Chemistry, Indian Institute of Technol- ogy Roorkee, Roorkee 247 667, India. Tel.: +91 1332 285801; fax: +91 1332 273560. E-mail addresses: vinodfcy@iitr.ernet.in, vinodfcy@gmail.com (V.K. Gupta). to presence of different donor atoms, cavity size, ligand geome- try to guest ions, remarkable selectivity, sensitivity and stability for specific ion. Thus, Schiff bases have been used as ionophores in PVC based sensors for determining the rare earth metals such as Gd 3+ [4], Tb 3+ [5], Ce 3+ [6], Nd 3+ [7], Ce 3+ [8], La 3+ [9]. Recently our group has developed a number of sensors for various ions [10–23]. In view of simplicity, wide range of applications of ion sensors, we explored two new Schiff bases: X 1 and X 2 as neutral ionophores in PVC based membranes for fabrication of Pm(III) selective sen- sors. The proposed sensor has excellent features like selectivity, sensitivity and response time. 2. Experimental 2.1. Reagents and materials Analytical grade o-nitrophenyloctylether (o-NPOE), potassium tetrakis (p-chloropheny1) borate (KTpClPB), sodiumtetraphenylb- orate (NaTPB), oleic acid (OA) isophthalaldehyde and high molecular weight polyvinyl chloride (PVC) were purchased from Fluka and used as received. Chloronaphthalene (CN) and tri-(2- ethylhexyl) phosphate (TEHP) were obtained from High-media laboratories (Mumbai, MH, India); dioctylphthalate (DOP), di- n-butylphthalate (DBP) and dibutyl butylphosphonate (DBBP) were obtained from SD-Fine Chem. Limited (Mumbai, MH, India). Cetryltrimethylammonium-bromide (CTAB), sodium salt of ethylenediaminetetraacetic acid (Na 2 EDTA), (1R, 2R)-1, 2- 0003-2670/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2010.09.037