A simple sequential injection (SI) method is reported for the determination of the non-ionic surfactant polyoxyethylene sorbitan monoleate (Tween-80). The proposed method is based on a fluorescence enhancement of the probe 4′,5′-dibromo-2′,7′-dinitro fluorescein, disodium salt (Eosin B) in the presence of a surfactant. The procedure is optimized using the univariate method of optimization. The optimum operating conditions are as follows: reagent concentration, 40 ppm; pH, 4.5; aspirated volumes of sample and reagent, 120 μL and 100 μL, respectively. With the optimum conditions described, linear calibration curves were obtained from 10 - 200 ppm. The detection limit was 1.7 ppm and the maximum relative standard deviation of the method was 2.7% (n = 5). The fluorescence excitation and emission were fixed at λex = 545 nm and λem = 585 nm. The method was successfully applied to the determination of (TW-80) in natural water samples.
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