DETERMINATION OF THORIUM AND URANYL IN NITROPHOSPHATE SOLUTION BY ONLINE MATRIX-ELIMINATION REVERSED-PHASE CHROMATOGRAPHY

A reversed-phase chromatographic method combined with an on-line matri x-elimination procedure is described for the determination of thorium and uranium in the nitric acid digest of phosphate rocks, Phosphate an d other anions were first removed from the sample solution using a cat ion-exchange pre-column to bind cations in the sample and a dilute nit ric acid eluent to elute the anions. In the second stage of the proced ure, a short C-18 column was employed with a phenylhydroxyacetic acid solution used as the washing eluent. Thorium(IV) and uranyl were trapp ed on the C-18 column whilst the transition and lanthanide metals pres ent were flushed to waste due to their weaker retention. In the final step thorium(IV) and uranyl were transferred onto a reversed-phase C-1 8 column, where they were separated and quantified using alpha-hydroxy isobutyric acid eluent with visible detection at 658 nm after post-col umn reaction with Arsenazo III. The entire procedure was performed aut omatically using a programmable HPLC pump.