Analytica Chimica Acta 582 (2007) 147–153 Ion imprinted polymer based sensor for monitoring toxic uranium in environmental samples P. Metilda a , K. Prasad a , R. Kala a , J.M. Gladis a , T. Prasada Rao a,∗ , G.R.K. Naidu b a Regional Research Laboratory (CSIR), Trivandrum 695019, India b Sri Venkateswara University, Tirupati 517502, India Received 6 July 2006; received in revised form 25 August 2006; accepted 25 August 2006 Available online 1 September 2006 Abstract In view of the extreme toxicity of uranium and consequent stringent limits fixed by WHO and various national governments, it is essential to monitor the uranium content in the environment which is at ultratrace levels. Conventional ionophore based ion selective electrodes, barring a few, have limitations in terms of sensitivity and selectivity for the above mentioned purpose. We now propose an ion imprinted polymer (biomimetic) based potentiometric sensor by dispersing the uranyl ion imprinted polymer particles in 2-nitrophenyloctyl ether (plasticizer), which is embedded in polyvinyl chloride matrix. The sensor responds to uranyl ion over a wide concentration range of 2.0 × 10 -8 to 1.0 × 10 -2 M. The limit of detection was 2.0 × 10 -8 M. It showed a good selectivity for uranyl ion over alkali, alkaline earth, transition and heavy metal cations. The sensor is successfully tested for the monitoring of toxic uranium in tap and sea water samples. © 2006 Elsevier B.V. All rights reserved. Keywords: Uranium; Ion imprinted polymer; Sensors; Potentiometry; Natural and sea waters 1. Introduction Uranium and its compounds, like lead are highly toxic and results in progressive or irreversible renal injury and in acute cases, may lead to kidney failure and death. The tolerable daily intake of uranium established by WHO based on Gilman’s stud- ies is 0.6 g kg -1 of body weight per day [1–3]. The WHO, Health Canada and Australian drinking water guidelines have fixed the maximum uranium concentration in drinking water to be less than 9, 20 and 20 gL -1 , respectively [1,2]. The design and development of portable devices such as sensors rather than laboratory based instruments for the monitoring of uranium at trace/ultratrace level is a prime challenge to environmental chemists. Potentiometric sensors make use of the development of an electrical potential at the surface of the electrode, when it is placed in a solution containing ions that can exchange with the surface. These potentiometric ion selective electrodes (ISE) are perhaps the most commercially successful chemical sensors. A few ISEs [4–6] have been developed for the potentiometric determination of uranium, wherein membranes were prepared ∗ Corresponding author. Tel.: +91 471 2515317; fax: +91 471 2491712. E-mail address: tprasadarao@rediffmail.com (T.P. Rao). with increasingly selective ionophores, which sense the analyte selectively. One of the main reasons for the traditional ISEs not becoming that much popular is the difficulty in tuning the selec- tivity. An alternative approach involves the use of biomimetic receptor systems or plastic antibodies capable of binding target analytes with high affinities and selectivities on par with natural receptors [7,8]. These imprinted polymers or plastic antibodies are much more stable to organic solvents, pH, high temperatures and pressures than their biological counterparts. Moreover, the preparation of these materials is cost effective and these can be stored in dry state at room temperature for long periods of time. With such virtues, ion imprinted polymer (IIP) materials, though in its infancy, have been employed recently for solid phase extraction, sensor and membrane separation applications [8–10]. IIPs are classified into four groups based on the inclusion of chelating ligand in polymer matrix: viz., (i) crosslinking of bifunctional reagent with linear chain polymers, (ii) chemical immobilization, (iii) surface imprinting and (iv) trapping [9]. Rosatzin et al. and Murray et al. have described IIP based poten- tiometric sensors for calcium and magnesium [11] and uranium and lead [12]. These sensors are based on the use of IIP particles prepared via chemical immobilization after isolation of binary complexes of the metal ions with ligands having vinyl groups and then polymerization with matrix forming monomers. Recently, 0003-2670/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2006.08.052