Flow injection online spectrophotometric determination of uranium after preconcentration on XAD-4 resin impregnated with nalidixic acid

In this work, spectrophotometer was used as a detector for the determination of uranium from water, biological, and ore samples with a flow injection system coupled with solid phase extraction. In order to promote the online preconcentration of uranium, a minicolumn packed with XAD-4 resin impregnated with nalidixic acid was utilized. The system operation was based on U(VI) ion retention at pH 6 in the minicolumn at flow rate of 15.2 mL min ^-1. The uranium complex was removed from the resin by 0.1 mol dm ^-3 HCl at flow rate of 3.2 mL min^-1 and was mixed with arsenazo III solution (0.05 % solution in 0.1 mol dm^-3 HCl, 3.2 mL min^-1) and driven to flow through cell of spectrophotometer where its absorbance was measured at 651 nm. The influence of chemical (pH and HCl (as eluent and reagent medium) concentration) and flow (sample and eluent flow rate and preconcentration time) parameters that could affect the performance of the system as well as the possible interferents was investigated. At the optimum conditions for 60 s preconcentration time (15.2 mL of sample volume), the method presented a detection limit of 1.1 μg L^-1, a relative standard deviation (RSD) of 0.8 % at 100 μg L^-1, enrichment factor of 30, and a sample throughput of 42 h^-1, whereas for 300 s of the preconcentration time (76 mL of sample volume), a detection limit of 0.22 μg L^-1, a RSD of 1.32 % at 10 μg L^-1, enrichment factor of 150, and a sampling frequency of 11 h^-1 were reported.