Rapid and simultaneous determination of neptunium and plutonium isotopes in environmental samples by extraction chromatography using sequential injection analysis and ICP-MS

This paper reports an automated analytical method for rapid and simultaneous determination of plutonium isotopes (239Pu and 240Pu) and neptunium (237Np) in environmental samples. An extraction chromatographic column packed with TrisKem TEVA® resin was incorporated in a sequential injection (SI) system for the isolation of plutonium and neptunium from matrix elements and interfering nuclides.

Valence adjustment is a crucial step to ensure the same chemical behavior of plutonium and neptunium onto the TEVA column and consequently to accomplish their simultaneous separation and detection. Distinct procedures were investigated and compared for the adjustment of oxidation states of plutonium and neptunium to Pu(IV) and Np(IV), respectively.

A two-step protocol using sulfite and concentrated nitric acid as redox reagents was proven to be the most effective method. The analytical results for both plutonium and neptunium in three reference materials were in agreement with the recommended or literature values at the 0.05 significance level.

The developed method is suitable for the analysis of up to 10 g of soil and 20 g of seaweed samples. The extraction chromatographic separation within the SI system for a single sample takes less than 1.5 h. As compared to batchwise procedures, the developed method significantly improves the analysis efficiency, reduces the labor intensity and expedites the simultaneous determination of plutonium and neptunium as demanded in emergency actions.