Optical fibre fluorosensor for cadmium with diethylaminoethyl-Sephadex as a substrate

Abstract

An optical fibre fluorosensor for cadmium ion was prepared by immobilizing 8-hydroxy-7-iodoquinoline-5-sulfonic acid on diethylaminoethyl (DEAE) Sephadex. Owing to the lowest excited singlet changing from n–π^* to π–π^*, complexation between cadmium ion and the immobilized reagent resulted in a weakly fluorescent ligand becoming a strongly fluorescent complex. Based on the fluorescence intensity change of the immobilized phase at 505 nm, cadmium ion in solution was determined. The characteristics of the fluorosensor were studied by using both the kinetic and equilibrium methods. As DEAE-Sephadex is a colourless and transparent gel containing diethylaminoethylglucan with a low transfer resistance in water, the fluorosensor reached 90% of the steady-state response in 10 s. The relationship between the response and the logarithm of cadmium ion concentration was linear in the range of 2.0 × 10^–7–7.0 × 10^–5 mol dm^–3. The detection limit for Cd^II was 8.0 × 10^–8 mol dm^–3. Using KI solution, the sensing layer saturated by cadmium ion can be regenerated, but the immobilized 8-hydroxy-7-iodo-quinoline-5-sulfonic acid was not destroyed. The results of this study demonstrate that DEAE-Sephadex is a good substrate for an optical fibre fluorosensor for cadmium ion. With appropriate separation it can be applied to the determination of cadmium ion in flour samples.