Journal of Hazardous Materials 173 (2010) 110–114 Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat An optical chemical sensor for thorium (IV) determination based on thorin S. Rastegarzadeh ∗ , N. Pourreza, I. Saeedi Department of Chemistry, College of Science, Shahid Chamran University, Ahvaz, Iran article info Article history: Received 2 February 2009 Received in revised form 12 August 2009 Accepted 13 August 2009 Available online 20 August 2009 Keywords: Optical sensor Optode Thorium Thorin Methyltrioctylammonium chloride Triacetylcellulose abstract A selective method for the determination of thorium (IV) using an optical sensor is described. The sensing membrane is prepared by immobilization of thorin–methyltrioctylammonium ion pair on triacetylcel- lulose polymer. The sensor produced a linear response for thorium (IV) concentration in the range of 6.46 × 10 -6 to 9.91 × 10 -5 mol L -1 with detection limit of 1.85 × 10 -6 mol L -1 . The regeneration of optode was accomplished completely at a short time (less than 20 s) with 0.1 mol L -1 of oxalate ion solution. The relative standard deviation for ten replicate measurements of 2.15 × 10 -5 and 8.62 × 10 -5 mol L -1 of thorium was 2.71 and 1.65%, respectively. The optode membrane exhibits good selectivity for thorium (IV) over several other ionic species and are comparable to those obtained in case of spectrophotometric determination of thorium using thorin in solution. A good agreement with the ICP-MS and spiked method was achieved when the proposed optode was applied to the determination of thorium (IV) in dust and water samples. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Thorium is a radio element that is often used as a fuel for nuclear reactors besides its industrial applications. The main sources of tho- rium in nature are soil, rocks, plants, sand and water [1,2]. Normally, very little amounts of thorium in lakes, rivers and oceans get into the fish or seafood. But there may be more thorium than normal near an uncontrolled hazardous waste site which could have acute toxicological effects for human. The continuous exposure to tho- rium may cause an increased chance of developing cancer of the lung, pancreas or bone and changes in genetic material of body cells [3]. Thus, the analytical determination of this element is use- ful in environmental science and also in view of their applications in geochemistry and nuclear fuel chemistry. The determination of thorium by the instrumental techniques such as ICP-AES, ICP-MS and NAA is still difficult because of insuf- ficient sensitivity, lack of selectivity, presence of complex matrix, poor precision and accuracy [4–7]. In recent years, among a wide variety of methods, optical sensors (optodes) have been applied to various heavy metal assays [8–10]. The optodes have gained notable practical reliability and can be considered as inexpensive alternative to certain conventional ana- lytical methods. These sensors are simple devices that use chemical sensing elements and optical transduction for the signal processing. The optical sensors offer further advantages as freedom from elec- ∗ Corresponding author. Fax: +98 611 3331042. E-mail addresses: rastegarz@yahoo.com, rastegarz@scu.ac.ir (S. Rastegarzadeh). trical noise and ease of miniaturization, as well as the possibility of remote sensing [11]. Polymers have been widely used as support materials for a broad range of optical sensors. They have many desirable features and compare well with sol–gel matrices for most applications [12,13]. Because of their transparency, the polymers are most often used in optodes with visible spectrophotometric detections. The most widely used polymers in optical sensors are polyvinyl chloride (PVC) [14–16] and cellulose derivatives such as acetylcellulose [17–20]. Many factors must be controlled for preparation of a good optode based on a PVC membrane, particularly the solubil- ity parameter of additives [21], whereas, the optical sensor based on acetylcellulose is prepared easily in a short time. Optical sensors using polymer membrane containing an ionophore that form a complex with the analyte to produce a dis- tinctive color change are of great interest for the trace analysis of heavy metal ions. Most of these ionophores are water solu- ble. Therefore their immobilization into or onto a solid support is an important factor for producing a suitable sensing membrane. Among different strategies, the lipophilization of the ionophore molecule by formation of an ion pair is the most commonly used method which can slow down the process of leaching [22–24]. A few optical sensors for the determination of thorium have been reported in the literature. Safavi and Sadeghi [25] described a thorium sensing membrane by incorporating 4-(p- nitrophenylazo)-pyrocatechol as ionophore in plasticized PVC. The proposed optical sensor displays a linear range of 8.66 × 10 -6 to 2.00 × 10 -4 mol L -1 of thorium with a limit of detection of 6 × 10 -6 mol L -1 . In another research Khayatzadeh Mahani et 0304-3894/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2009.08.055