Perspectives on the Use of Liquid Extraction for Radioisotope Purification

Abstract

The reliable and efficient production of radioisotopes for diagnosis and therapy is becoming an increasingly important capability, due to their demonstrated utility in Nuclear Medicine applications. Starting from the first processes involving the separation of 99mTc from irradiated materials, several methods and concepts have been developed to selectively extract the radioisotopes of interest. Even though the initial methods were based on liquid-liquid extraction (LLE) approaches, the perceived difficulty in automating such processes has slowly moved the focus towards resin separation methods, whose basic chemical principles are often similar to the LLE ones in terms of chelators and phases. However, the emerging field of flow chemistry allows LLE to be easily automated and operated in a continuous manner, resulting in an even improved efficiency and reliability. In this contribution, we will outline the fundamentals of LLE processes and their translation into flow-based apparatuses; in addition, we will provide examples of radioisotope separations that have been achieved using LLE methods. This article is intended to offer insights about the future potential of LLE to purify medically relevant radioisotopes.

Highly Efficient Micro-Scale Liquid-Liquid In-Flow Extraction of 99mTc from Molybdenum

“…The current trend in technology aiming to achieve even more compact systems is leading to the development of micro-scale reactors (lab-on-chip) in the field of radiochemical separation and radiopharmaceutical production, in order to improve performance and minimize chemical and radiological risks [ 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ]. In this view, a latest generation device, the membrane-based Liquid–Liquid separator, 10 September ( Figure 1 ), patented and produced by ZAIPUT Flow Technologies company (Cambridge, MA, USA), has been recently used for the radiochemical separation of radioisotopes of nuclear medical interest [ 23 , 29 , 30 , 32 ], for the miniaturization of liquid–liquid extraction processes in an in-flow chemistry regime.…”

“…The in-flow extraction process carried out at the micro-scale level creates some advantages when compared to similar processes performed on a macro-scale, including: shorter extraction times, an increase in the mass transfer coefficient, a better surface-volume interface ratio (S/V), etc. [ 31 , 33 , 34 , 35 , 36 ].…”

Continuous Flow Upgrading of Selected C2–C6Platform Chemicals Derived from Biomass

“…In addition, in-line liquid−liquid or liquid−gas separation relies on various technologies including (automated) settling tanks, 98,1080−1083 evaporators, 178,1084 and membrane-based technologies. 65,98,1077,1085 Liquid−liquid extraction is one of the most important, applied, and mature unit operations in the (bio)chemical industry. The separation method is based on the different solubility of compounds between two immiscible fluids.…”

“…Subsequent separation is envisaged by simple decantation, 98,1080−1083 flow splitters that separate the two phases e ffi c i e n t l y , 1 0 9 7 o r m e m b r a n e -b a s e d s e p a r ators. 65,98,1077,1085,1105,1106 The potential of such liquid−liquid microextractor/reactors is based on the superior performance and greater efficiency observed in terms of mass transfer coefficients in comparison with conventional contactors. 1097 The application of this technology has been extended to perform extractions 1097,1107−1109 or reactive extraction.…”

“…Nevertheless, in-line liquid–liquid separation extraction is the only separation technique that was successfully applied for the separation of a range of compounds that fit the scope of this review. In addition, in-line liquid–liquid or liquid–gas separation relies on various technologies including (automated) settling tanks, ,− evaporators, , and membrane-based technologies. ,,, …”