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 mu g L-1. The relative standard deviation (RSD, %), calculated from replications of the experiment under recommended conditions (n = 10; 20 mu g 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 Caetit & eacute;, 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.