Analytical Sciences

Simultaneous Spectrophotometric Determination of Uranium and Thorium by Flow Injection Analysis Using Selective Masking

Yoshihiro HIRANO,  Yuichi OGAWA, and Koichi OGUMA

Department of Materials Technology, Faculty of Engineering, Chiba University, Yayoi-cho, Inage, Chiba 263-8522, Japan

A flow injection system for the simultaneous determination of uranium and thorium has been developed by using selective masking and a spectrophotometric detector with two flow cells aligned with the same optical path. The injected sample solution was first mixed with a reagent solution containing Chromazurol S (CAS) and cetyltrimethylammonium chloride (CTMAC), and the total absorbance of uranium- and thorium-CAS complexes was measured in the first flow cell at 620 nm. The sample stream was then mixed with an EDTA solution in order to convert the thorium-CAS complex to a thorium-EDTA complex, and the absorbance of the uranium-CAS complex was measured in the second flow cell. The detection limits were 10 ug dm^-3 for uranium and 7 ug dm^-3 for thorium. The calibration graphs were linear (r < 0.9998) at least over the ranges of 0.1 to 10 mg dm^-3 for uranium and 0.08 to 8 mg dm^-3 for thorium. The RSDs were less than 1.5% (n = 3) in the calibration range. Uranium and thorium of up to the 6-fold concentration to each other could be determined in admixtures with relative errors of less than 3.3%. The sample throughput was 24 per hour. The proposed system was successfully applied to the analysis of a uranium-thorium ore mock solution by coupling with anion-exchange in a magnesium nitrate medium to eliminate interference from coexisting elements.

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