A rapid sequential chromatographic separation of U- and Th-decay series radionuclides in water samples

A new sequential protocol for the separation and preconcentration of U, Th, Ra, Po and Pb for the same sample aliquot has been designed. The optimized stacking of chromatographic resins [TRU, Sr and a new hybrid Ra resin (composed of Analig Ra-01 and cation exchange AG50Wx8)] enables a rapid loading of the sample (less than 75 min for 300 mL of samples) while ensuring a high retention of the analytes of interest. The use of a hybrid Ra resin allows the complete and selective extraction of Ra on a solid support, a feature lacking in other sequential separation procedures. A loading medium composed of 1 M HNO₃ and chloride ions (as NH₄Cl) was found suitable for the retention of all analytes of interest onto the stacked chromatographic resins. The proposed elution conditions facilitate the complete segregation of individual elements in 5 distinctive fractions, reducing the risk of spectral and non-spectral interferences. This feature enables the proper quantification of the radioisotopes either by ICP-MS or alpha spectrometry below national and international regulatory guidelines. The mean chemical recoveries for the separation are 93, 98, 105, 88, and 98% for U, Th, Ra, Po and Pb, respectively. Reproducible yields were obtained independently of the water type tested, demonstrating the versatility and the robustness of the proposed methodology.