Field-deployable spectrophotometric determination of uranium in aqueous systems using Br-PADAP

The 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Br-PADAP) spectrophotometric method is widely employed for uranium (U(VI)) determination due to its high sensitivity. However, conventional protocols require toxic sodium fluoride as both a masking agent and a stabilizer, posing environmental and operational risks. To address this limitation, we developed an eco-friendly alternative utilizing low-toxicity sodium dodecyl sulfonate (SDS) for dual-functional masking and stabilization. Critical parameters including pH, reagent stoichiometry, and reaction kinetics were systematically optimized. The Br-PADAP-U(VI) complex exhibited maximum absorbance at 576 nm (ε = 4.33 × 10⁴ L mol^-1 cm^-1), with rapid color development and stable signal retention (>4 h) under ambient conditions. Linear Beer-Lambert compliance was observed within 0.0-4.0 μg per mL U(VI), yielding a Sandell sensitivity of 0.0055 μg cm^-2. Notably, the method demonstrated exceptional tolerance toward coexisting ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, Fe³⁺, Cl^-, CO₃^2-, and Cr₂O₇^2-). Validation via spike-recovery tests in environmental water samples achieved 96.4-104% recoveries (0.5%< RSD <2%), confirming the reliability for field-deployable U(VI) quantification with advantages of simplicity, rapidity, and accuracy.