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.

Synergistic Extraction of Europium (III) using Di-n-Butylsulfoxide and Picrolonic Acid.

AIM AND OBJECTIVE: Europium (Eu(III)) is a rare-earth metal, the softest, least dense, and most volatile member of lanthanides. It is greatly applied in the control rods of nuclear reactors. Although various extraction methods of Eu(III) have been reported, we present a novel mixture of easily available extractants in optimized experimental conditions to extract it efficiently, quickly, and cost-effectively. MATERIALS AND METHODS: Physical-chemical conditions (e.g., pH, equilibration time, temperature, europium concentration, extractants concentration, presence of specific metal ions) were optimized. The extractants, picrolonic acid (HPA) and di-n-butylsulfoxide (DBSO), were thoroughly mixed at equal concentration in chloroform. Standard Eu(III) solution was used for determining the method's accuracy. Reagent blank was prepared under identical conditions but without metal ions. Using the metallochromic dye arsenazo III as the blank, the absorbance of Eu(III) was measured spectrophotometrically at 651 nm. The distribution ratio (i.e., Eu(III) concentration in the aqueous phase before and after extraction) defined the extraction yield. RESULTS: HPA/DBSO mixture (0.01 M) had a synergistic effect on Eu(III) extraction (1.19×10-5 mole/dm3), achieving a maximum yield (≥ 99%) at pH 2, during 5 minutes equilibration at room temperature. Eu(III) extraction was reduced depending on the nature but not on the metal ions concentration. Extractants could be recycled four times without consequent degradation. Deionized water (dH2O) was the best strippant besides its availability and low-cost. The composition of the extracted adduct was defined as Eu(PA)3.2DBSO. CONCLUSION: This alternative method was found to be stable, simple, rapid, cost-effective, reliable, accurate and sensitive. It could be used for Eu(III) extraction and refining on a pilot plant scale.

Spectrophotometric determination of uranium with arsenazo-III in perchloric acid.

A short, sensitive and reliable spectrophotometric method, which has advantages over all known "wet chemistry" methods for uranium determination with regard to tolerance to common interferences, has been developed for the determination of uranium. Selectivity, molar absorptivity and the determination range of uranium have been enhanced by using 0.07% arsenazo-III as a chromogenic reagent. The use of 3 mol dm(-3) perchloric acid as a medium of determination was found to be excellent in terms of good solvent compatibility on dilution, destruction of organic contamination and simplicity of operation. The uranium-arsenazo-III complex formed instantly, and was found to be stable for more than 3 weeks with constant absorbance. Beer's law was obeyed up to a uranium concentration of 16 microg g(-1), with a molar absorptivity at 651 nm of 1.45x10(5) mol(-1) dm(3) cm(-1) at 24+/-2 degrees C. Only phosphate and citrate at 70-fold excess over uranium interfere seriously, whereas other anions studied could be tolerated up to a 70-fold excess over uranium. Of the cations studied, only Mn(II), Co(II), Ni(II), Cu(II) and Cr(III) decreased the normal absorbance of the complex. Iron(III), Ce(III) and Y(III) enhanced the absorbance. Other cations studied did not affect the absorbance up to a 50-fold excess. The accuracy was checked by determining uranium from standard solutions in the range 10-50 microg g(-1). It was found to be accurate with a 96.0-98.6% recovery rate. The method has been successfully applied to standard reference materials and ore samples at microg g(-1) levels.