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Abstract
Environmental plutonium was determined by ICP‐MS after countercurrent chromatography (CCC) preseparation with 20% tri‐n‐octylamine in toluene as stationary phase. The matrix elements, thorium and uranium, were eluted by using 7.5 mol/L nitric acid, 10 mol/L hydrochloric acid, and 3 mol/L nitric acid, respectively, and the plutonium was quantitatively stripped by using 0.025 mol/L oxalic acid–0.15 mol/L nitric acid. The spectral interferences due to the tailing of adjacent actinoids, polyatomic ion, and the matrix effect were depleted after the sample was subjected to the CCC preseparation because uranium and thorium were well separated with decontamination factors of 104 and 105, respectively; the memory effect could be eliminated effectively with a solution with the same composition of plutonium eluant. Isotopic dilution was used to determine ultra‐trace 239Pu using 242Pu as the spike. The limit of detection of 239Pu is 6 fg (27 attomoles), and the limit of determination is 25.5 fg for soil. The depth profile of 239Pu was revealed with maximum 239Pu concentrations of ∼0.08 × 10−12 g/g (0.3 femtomole per g) in Xi'an and ∼1.6 × 10−12 g/g (6.7 femtomole per g) in Gansu, China. The ratio of 240Pu/239Pu in the soil sampled from Gansu differs from the mean value of the global fallout, indicating a different origin.