A pre-concentration procedure using cloud point extraction for the determination of uranium in natural water

A pre-concentration procedure using cloud point extraction is presented for the determination of uranium in natural water using molecular absorption spectrometry. The ligand used was 2-(5-bromo-2-pyridylazo)-5-(diethylamino)-phenol (Br-PADAP) and the micellar phase was obtained using the non-ionic surfactant octylphenoxypoly-ethoxyethanol (Triton X-114) and centrifugation. Interferences were eliminated using a masking solution containing trans-1,2-cyclohexanediaminetetraacetic acid (CDTA), sodium fluoride and sulphosalicylic acid. The optimization step was performed using a two-level factorial design and a Doehlert matrix, involving the factors pH, centrifugation time and buffer concentration. The method allows the determination of uranium in water samples with a detection limit of 0.15 mu g L-1, a quantification limit of 0.50 mu g L-1 and a precision expressed as relative standard deviation of 1.8 and 2.3% for uranium concentrations of 5 and 10 mu g L-1, respectively (n = 8). The accuracy was confirmed by analysis of two certified samples of natural water. This method was applied to the determination of uranium in superficial water samples collected at a uranium mine in Brazil. For five samples analyzed, the concentration of uranium varied between 1.1 and 18.1 mu g L-1. Tests of addition/recovery were performed for all these samples, and the results varying between 98 and 105% also proved that this procedure is not affected by the matrix and can be applied satisfactorily to the determination of uranium in water samples.