Fig. 1-3 The world's first plutonium ion selective electrode (Pu3+-ISE) A Pu3+ sample solution is separated from the Pu3+ standard solution by a liquid membrane containing a special complexing agent. The potential difference measured between the sample and standard solutions by using two reference electrodes, reflects the potential difference generated at the sample solution/membrane interface, which depends on the concentration of Pu3+ in the sample solution.

Fig. 1-4 The concentration range measurable by the Pu3+-ISE It is possible to determine precisely the Pu3+ of a wide concentration range based on the measurement of the potential difference at the Pu3+-ISE interface even in the presence of a considerable amount of H+.

Ion sensors have been shown to monitor for ion concentrations varying hour by hour and play important roles in the fields of process control of plants, understanding of the dynamic feature of the environment, clinical diagnosis, etc. One of the typical ion sensors is referred to as the ion selective electrode (ISE) which is based on the following principle. The potential difference (E) generated at the sample solution/electrode interface responds to the objective ion (iz) selectively and E is proportional to the logarithm of the concentration of iz. In this research, on the basis of the fundamental elucidation of the potential generating process at the ISE, an ISE has been developed first in the world for the continuous and precise determination of the trivalent plutonium ion (Pu3+) in a wide concentration range (10-7 to 10-2 M) by using a simple procedure. This Pu3+-ISE has some advantages that it can be set easily in a glove-box, shielding cave or pipe of a plant line and is easily handled by remote procedure. Since the ISE responds very selectively to Pu3+ and can be used even in the presence of uranium and hydrogen ions of high concentrations, the ISE is expected to be very useful for the precise control of processes in reprocessing or mixed-oxide fuel production plants, as well as for the precise and accurate determination of plutonium. The ISE is also expected to contribute largely to the development of research in the field of solution chemistry or electrochemistry. One of reasons why the above-described functions of Pu3+-ISE were attained is attributable to the introduction of bis-(diphenylphosphoryl)-methane as a specific complexing agent for Pu3+ in the ISE membrane. The agent had been chosen on the basis of knowledge on complex formation of plutonium.

Reference Y. Kitatsuji et al., Plutonium(III)-Ion Selective Electrode of Liquid Membrane Type Using Multidentate Phosphine Oxide Ionophore, Anal. Chim. Acta., 387, 181 (1999).

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