Determination of trace uranium by a photo-catalytic resonance fluorescence method coupled with dual cloud point extraction

In this study, two types of salophens (SA) with different solubilities were synthesized, and they all can combine with uranyl to form stable complexes: [UO22+–SA1] and [UO22+–SA2]. Among them, [UO22+–SA1] was used as ligand to extract uranium in complex samples by dual cloud point extraction (dCPE), and [UO22+–SA2] was used as a catalyst for determining uranium by a photo-catalytic resonance fluorescence (RF) method. The photo-catalytic characteristic of [UO22+–SA2] on the oxidized Rhodamine G (RhG) by potassium bromate led to an RhG RF intensity decrease. The reduced value for the RF intensity of the reaction system (ΔF) was proportional to the uranium concentration (c), and a novel photo-catalytic RF method was developed for determining trace uranium(VI) after dCPE. The combination of photo-catalytic RF techniques and dCPE procedure provided enhanced sensitivity and selectivity to the present method. Under the optimal conditions, the linear calibration curves range was 0.040 to 40.0 ng mL−1. The limit of detection was 0.035 ng mL−1. The proposed method was successfully applied for separating and determining uranium in real samples with 91.3–107.3% recovery. The mechanisms of reaction and extraction are discussed.