Room temperature phosphorimetric determination of bromate in flour based on energy transfer Mario Menendez-Miranda, Maria T. Fernandez-Argüelles n , Jose M. Costa-Fernandez n , Rosario Pereiro, Alfredo Sanz-Medel Department of Physical and Analytical Chemistry, University of Oviedo, Avda. Julian Claveria 8, Oviedo E-33006, Spain article info Article history: Received 4 March 2013 Received in revised form 7 May 2013 Accepted 10 May 2013 Available online 20 May 2013 Keywords: Luminescence Energy Transfer Phosphorescence Bromate determination Sol–gel Phosphorescence sensing abstract Determination of bromate ions in contaminated flour samples by using a room temperature phosphor- escence (RTP) optosensor is described. The optosensor is based on the non-radiative energy transfer from α-bromonaphthalene (a phosphorescent molecule insensitive to the presence of the analyte) acting as donor, to an energy acceptor bromate-sensitive molecule (trifluoperazine hydrochloride). The RTP emission of the selected donor greatly overlaps with the absorption spectrum of the acceptor, resulting in a decrease of the measured signal as the concentration of bromate ions increases. A simple and general procedure is proposed to carry out the incorporation of both the donor and acceptor molecules in an appropriate solid material (sensing phase) through the co-immobilization of the species in a sol–gel inorganic matrix. The optimum amounts of the sol–gel precursors, including silica precursors, type of catalysis, and concentrations of donor and acceptor molecules, have been evaluated in order to obtain the best analytical features of the proposed optosensor for bromate determination. The highly stable developed sensing phase shows a selective and reversible response towards bromate even in presence of dissolved oxygen (a well-known quencher of the RTP). The calibration graphs were linear up to 200 mg L -1 , with a detection limit for bromate dissolved in aqueous medium of 0.2 mg L -1 . Sample throughput of the proposed optosensor was about 18 measurements h -1 . Application of the developed sensing phase was successfully proved for the detection of bromate ions in commercial flours, obtaining good recoveries. & 2013 Elsevier B.V. All rights reserved. 1. Introduction It is widely known that the bread making quality of freshly milled flour improves after two months storage. However, this process can be carried out faster through the addition of chemical substances called improvers [1]. Among these improvers, potas- sium bromate is commonly added because it is a slow-acting oxidizer that contributes to its functionality throughout the mix- ing, fermentation and proofing stages. Moreover, it presents an important residual action during the early stages of baking, resulting in strengthen dough and allowing for greater oven spring and higher rising in the oven [2]. However, there is a concern regarding the use of bromates in baking due to its possible relation to the development of tumors in laboratory animals, and therefore, European, American and Chi- nese regulations have limited its use. In this sense, the Code of Federal Regulations of the U.S. Food and Drug Administration has restricted the amount of potassium bromate added in a quantity not exceeding 50 parts to each million parts of the finished bromated flour, and is added only to flours whose baking qualities are improved by such addition [3]. For this reason, the develop- ment or improvement of analytical methods for the determination of bromate ions at such levels in flours is a matter of great interest. A large number of analytical methods have been published exploiting ion chromatography coupled with accelerated solvent extraction [4], high performance liquid chromatography-inductively coupled plasma mass spectrometry [5], or ion chromatography with a conductivity detector [6]. However, those methodologies present some disadvantages such as the need for extraction of the bromate ions at high temperatures [4], sophisticated instrumentation not affordable for many laboratories [5], or time consuming analytical strategies [6]. Room temperature phosphorescence (RTP) offers interesting advantages over fluorimetric-based methods that makes it attrac- tive for analytical applications [7]. For instance, the phosphores- cence signal is a low-noise emission because it is measured after any short-lived background luminescence or scattered light has ceased, allowing lower detection limits (DLs). Besides, the long emission wavelength of the phosphorescence phenomena facilitates Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/talanta Talanta 0039-9140/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.talanta.2013.05.019 n Corresponding authors. Tel.: +34 985103474. E-mail addresses: fernandezteresa@uniovi.es (M.T. Fernandez-Argüelles), jcostafe@uniovi.es (J.M. Costa-Fernandez). Talanta 116 (2013) 231–236