The Analysis of Pu Isotopes in Seawater by Flow Injection High Resolution Inductively Coupled Plasma Mass Spectrometry

INTRODUCTION To estimate the long-term radiation dose to man due to artificial radionuclides, a detailed knowledge of their distribution in the environment is indispensable. From the viewpoint of toxicity and radiation damage to the human being, plutonium is by far the most important nuclide of the transuranic elements that has been released into the environment by nuclear weapons tests, satellite and reactor accidents and reprocessing of spent plant fuel. Among plutonium isotopes generally found in the environment, Pu and Pu are the two most important and abundant isotopes. Since the concentration of Pu isotopes in seawater is extremely low, large amounts of sample and long analysis time are necessary to determination in Pu presence. The analytical methods commonly used for Pu determination are alpha spectrometry (1), liquid scintillation counter (2) and mass spectrometry (3). Conventional alpha spectrometry and liquid scintillation counter, are generally the most widely used methods, however, they are incapable of distinguishing between Pu and Pu because their alpha energies are too close to be resolved. Therefore, we only know total Pu activity, which is the sum of Pu and Pu. For this, inductively coupled plasma mass spectrometry (ICP-MS) has recently been used as a powerful technique for the determination of Pu isotopes as well as the Pu isotope ratio in environmental samples (4, 5). ICP-MS has the advantages of simple separation chemistry, shorter analytical time and easier operation. Meanwhile, the interference effect of U reported by some researchers (6, 7) is one of the most serious problems to overcome in the application of the ID-ICP-MS to the determination of trace Pu in environmental samples. Although Eroglu et al. (8) have succeeded in the determination of Pu by ICP-MS for seawater with optimum sample separation procedures and measurement conditions, large amounts of seawater or high concentrations of seawater were used. Moreover, there is no on-line sample treatment method reported in the analysis of Pu by ICP-MS so far. In this work, the flow injection method coupled with isotope dilution (ID) HR-ICP-MS in the determination of Pu isotopes for small amounts of seawater has been studied. In addition, we intensively studied the development of a method to minimize the sample amount and automatic preconcentation of Pu.