(700a) Sifel-Based Microfluidic Platforms for Liquid-Liquid Extraction of Radioactive Metals

Radioisotopes of metals (e.g., Cu-64 and Y-86) produced employing the cyclotron are crucial in nuclear medicine for Positron Emission Tomography (PET) imaging.  The extraction of radioisotopes produced from the cyclotron involves dissolution of the target material (containing impurities) in an aqueous acid followed by separation of the isotope of interest from the bulk solution using liquid-liquid extraction (LLE).  Conventionally, the UNEX process has been developed to isolate radionuclides from an acidic waste [1-3].  However, the UNEX process is designed for large-scale separation of radionuclides and thereby requires considerable dilution of the radionuclide and requires large quantities of organic solvents.  In addition, the process requires large-scale radiation shielding resulting in large size of the equipment, as well as long times for interface stabilization and reduced kinetics resulting from dilution. 

These issues can be overcome by using microfluidic platforms that require low sample volumes (eliminating the need for excessive dilution), allow rapid interface stabilization, minimize the wastage of organic solvents, and enhance the extraction efficiency of radioactive metal resulting from high interfacial area and small diffusional lengths.  Specifically, we are interested in reactive extraction of isotope of interest (Cu-64) from the mixture in aqueous acid phase with the chelating agents into the organic phase [4, 5, 6].  In this work, we present on the design, development, and optimization of solvent resistant polymer-based microfluidic platform to enable LLE for separation of radioactive metals (e.g., Cu-64) of interest from the mixture obtained from the cyclotron. We developed polymer based microfluidic platforms over glass or silicon-based microfluidic platforms to enable simple and less involved fabrication procedure.  We systematically optimized several factors affecting the interface stability with the aid of an analytical model, including geometry of the micro-channel, surface functionalization, and the flow rates of the two immiscible streams as well as predicted extraction efficiencies as a function of different paramters.

In this work, we demonstrate the application of the developed microfluidic platform to extract radioactive copper (Cu-64) from an aqueous solution into a solution of a chelating agent in an organic solvent (e.g., 2-Hydroxy-4-n-octyloxybenzophenone Oxime in toluene) followed by back extraction into the aqueous phase [7].  We studied the effect of pH, contact time between the phases (length of the microchannel), concentration and the type of chelating agents, concentration of the isotope of interest, as well as of the impurities introduced in the solution on the extraction efficiency.  Radioactive dosimeter and ICP-OES or ICP-MS was used to quantify extraction efficiencies.  The developed microfluidic platforms provided quantitative information on the extraction process compared to conventional techniques, due to the superior control over the spatial and temporal properties of the interface and enabled rapid extraction times and high extraction efficiencies owing to minimal diffusion lengths.

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[2]    J. D. Law, R. S. Herbst, T. A. Todd, V. N. Romanovskiy, V. A. Babain, V. M. Esimantovskiy, I. V. Smirnov and B. N. Zaitsev, , Solvent Extraction and Ion Exchange 19 (2001) 23-36.

[3]    V. N. Romanovskiy, I. V. Smirnov, V. A. Babain, T. A. Todd, R. S. Herbst, J. D. Law and K. N. Brewer, Solvent Extraction and Ion Exchange 19 (2001) 1-21.

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[5]    T. Tasaki, T. Oshima and Y. Baba, Talanta 73 (2007) 387-393.

[6]    C. Priest, J. Zhou, R. Sedev, J. Ralston, A. Aota, K. Mawatari and T. Kitamori, International Journal of Mineral Processing 98 (2011) 168-173.

[7]    S. Goyal, A.V. Desai, R. Lewis, D. Ranganathan, H. Li, D.E. Riechert, and P.J.A. Kenis, in preparation.