Determination of uranium in water samples by energy-dispersive X-ray fluorescence spectrometry after solid-phase extraction

An analytical method is presented for determining the uranium concentration in water samples via energy-dispersive X-ray fluorescence (EDXRF) spectrometry after solid-phase extraction. For the preconcentration procedure, the 1-(-2-thiazolylazo)-2-naphthol (TAN) reagent was used to complex the analyte in the samples. After the percolation of the sample and retention of the complex on a C18 disk, analysis was performed directly on the solid phase via EDXRF. The pH, sample flow rate, and sample volume were analyzed in terms of the uranium extraction. Using a sample volume of 110.0 mL buffered at pH 6.5 and a flow rate of 1.0 mL min⁻¹, an enrichment factor (EF) of 645 was achieved, with a limit of detection of 1.5 μg L⁻¹. The relative standard deviation (RSD, %), calculated from replications of the experiment under recommended conditions (n = 10; 20 μg L⁻¹), was 10%. The results of the analyte addition and recovery tests varied between 98 and 117%. The accuracy of the method was verified via analysis of a water reference material, with no significant difference between the obtained values and the certified values (95% confidence level). The method was applied to groundwater, river water, and tap water samples collected in Caetité, Bahia, Brazil, and the results were compared with those obtained via inductively coupled plasma‒mass spectrometry (ICP‒MS). All the collected samples presented uranium concentrations below the acceptable maximum limit for drinking water samples.