Optode for uranium(VI) determination in aqueous medium

A colorimetric method for simultaneous preconcentration and determination of uranium(VI) anions from aqueous samples was developed using a membrane optode formed by physical inclusion of a chromophore 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP) into a plasticized cellulose triacetate matrix. The optode was tested for uranium uptake in bicarbonate/carbonate medium (∼10−4 M) at pH 7–8 in the presence of triethanolamine buffer. The inclusion of an anion-exchanger tricaprylylmethyl ammonium chloride (Aliquat-336) was found to be necessary for the formation of U(VI)–Br-PADAP complex in the optode matrix, resulting into distinct color change of the optode from yellow to magenta after uranium sorption. The composition of the optode was optimized by varying the amounts of different plasticizers and Aliquat-336 to obtain minimum response time towards U(VI) in aqueous bicarbonate medium. The proportionality in intensity of the magenta color of the optode samples loaded with varying amounts of U(VI) suggested its potential applications for screening of U(VI) in aqueous samples by visual colorimetry. The effects of experimental parameters involved in the detection and quantification of U(VI) using optode were optimized. The optode analytical performance was evaluated in terms of interference of cations and anions, equilibration time, reusability, detection limit, etc. and compared with the conventional spectrophotometric method for U(VI) using same chromophore Br-PADAP. The optode developed in the present work was tested in real alkaline Mg(NO3)2 effluent sample obtained from uranium extraction process.