Determination of Uranyl in Aqueous Solutions Using a Fiber-Optic-Based, Time-Resolved Luminescence Sensor

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Abstract
The use of time-resolved luminescence measurements is an effective way to determine a wide range of uranyl concentrations in aqueous samples. We have coupled this technique with the use of a remote optical sensing device, a “flow optrode,” by using fiber-optic cables in order to probe for uranyl in aqueous solutions. The flow optrode incorporates a Nation membrane through which UO2+2 can diffuse into a reaction/analysis chamber which contains phosphoric acid, a reagent which enhances the uranyl luminescence intensity and excited-state lifetime. The excited-state lifetime measurement provides information on the chemical environment within the sensor. Anionic quenchers are prohibited from entering the analysis cell because they cannot diffuse through the membrane. Fluorescing organic interferences can be eliminated by analyzing the emission signal at several microseconds after laser excitation. We were able to determine uranyl over a concentration range of 10−4 to 10−9 M using the flow optrode sensor.