This paper provides a comprehensive review of synergistic solvent extraction using crown ethers with a focus on the role of both extractants in facilitating cation-specific separations. An introduction to the various equilibria affecting synergistic extraction using crown ethers is followed by a review of the work published in this field during the 1972-1999 time period. The influence of various solvent extraction parameters on the potential for cation-selective synergism is critically examined. Those synergistic extractant combinations showing cation selectivity are highlighted, as are the fundamental investigations that are the foundation of the current understanding of synergistic solvent extraction using crown ethers.

Incorporating Size Selectivity into Synergistic Solvent Extraction: A Review of Crown Ether-Containing Systems

The synergism of trivalent actinides and lanthanides has been reviewed oritically. Different systems Including β-di-ketones and several other chelating agents with various neutral donors have been discussed. The thermodynamic parameters, effect of diluents, auto-synergism and synergism with eutectic mixtures have been discussed In the case of trivalent actinides and lanthanides. Also the mechanism of synergism and the various possible uses of this phenomenon have been referred to with the possible data available.

Synergism of trivalent actinides and lanthanides

99Mo/99mTc separation: An assessment of technology options

While the application of radionuclide generators in nuclear medicine constitutes a successful example of the availing of short lived radionuclides on demand, the success and growth of generator technology largely depend on the progress in separation science. Separation science plays a pivotal role in the development of radionuclide generators, with this branch of science being in a process of continuous evolution. Any breakthrough, technology innovation, or improvement over existing paradigms in separation science represent not only an important driving force but also lay the cornerstone for further accomplishments in radionuclide generator technology. With the emergence of professionally run central radiopharmacies, radionuclide generator technology is poised to undergo a game change in terms of design and user profiles. It is of utmost importance to assure the access to appropriate radionuclide generator systems that are adaptable to the existing and foreseeable demands of the nuclear medicine community. The purpose of this review is to assess the recent advances in separation science which can act as a springboard to spur further development in radionuclide generator technology. Such advances are expected to unfold a wide spectrum of radionuclide generators to accelerate further development in this field. In light of this, a variety of separation technologies that have traditionally been used and emerging techniques that have the potential to promote rapid growth in generator technology have been selected, highlighted, and critically evaluated to illustrate their impact on the development of clinically useful radionuclide generators. The advantages, limitations, and potential applications of the separation methods, along with their current status and future prospective in radionuclide generator development, are discussed.

Pivotal role of separation chemistry in the development of radionuclide generators to meet clinical demands

Amongst various radionuclides of molybdenum, 90Mo and 99Mo have suitable β energy for clinical uses. In this paper we report separation of 99Mo from 99Mo-99mTc equilibrium mixture. The liquid–liquid extraction technique has been employed using trioctylamine (TOA) diluted in cyclohexane as organic phase and HCl as aqueous phase. At 10−5 M HCl and 0.5 M TOA concentration 99mTc quantitatively transferred to the organic phase leaving 99Mo in the aqueous phase. The developed separation method is efficient and provides very high separation factor.

Separation of 99Mo and 99mTc by liquid–liquid extraction using trioctylamine as extractant

Separation of99Mo and99mTc can be performed with high selectivity using the crown ether 2,3,11,12-dibenzo-1,4,7,10,13,16-hexaoxacyclooctadeca-2,11-diene /DB18C6/ diluted with nitrobenzene. The high efficiency is attributed to the rather low extractability of molybdenum as compared with that of technetium.

On the separation of molybdenum and technetium. Crown ether as extraction agent

The extraction of technetium from ascorbic acid medium with dibenzene-18-crown-6 /DB-18C6/ and 18-crown-6 /18C6/ dissolved in benzene and nitrobenzene was studied. The effect of crown ether substition, concentration of the extracting agent as well as the pH of the aqueous solution on the distribution coefficient was investigated. Nitrobenzene was found to be a rather promising diluent.

Extraction of technetium from ascorbic acid medium with crown ethers

Separation of99Mo and99mTc was studied using a crown ether diluted with benzene mixed with acetonitrile. The effect of concentration of the extracting agent as well as the pH of the aqueous solution on the distribution coefficient was investigated. Benzene mixed with acetonitrile in 1∶3 ratio proved to be the best composition of the diluent. The extracted species has the general formula TcO2.nH2O.xCe.yC6H8O6.zCH3CN.

The effect of solvent mixture composition on the extractive separation of technetium using a crown ether

The extraction of technetium from ascorbic acid medium by dibenzene-18-crown-6 /DB18C6/ dissolved in benzene mixed with acetone in different ratios was studied. Benzene mixed with acetone in 1∶2 ratio proved to be the best composition of the diluent. The extracted species have the general formula TcO2.nH2O.xCE.yCH3COCH3.

Extraction of technetium from aqueous medium with the aid of crown ethers dissolved in benzene-acetone mixture

The synergism of the crown ethers /CE/ dibenzene-18-crown-6 /DB18C6/ and 18-crown-6 /18C6/ has been investigated in the thenoyltrifluoroacetone /HTTA/ extraction of technetium from aqueous phase containing NaBH4 into benzene at room temperature. The extracted synergistic species have the general formula TcO/OH/.TTA.CE. The order of synergism was found to be 18C6>DB18C6.

T. Lengyel

Papers

On the separation of molybdenum and technetium. Crown ether as extraction agent

Extraction of technetium from ascorbic acid medium with crown ethers

The effect of solvent mixture composition on the extractive separation of technetium using a crown ether

Extraction of technetium from aqueous medium with the aid of crown ethers dissolved in benzene-acetone mixture

Synergistic behaviour of crown ethers in the thenoyltrifluoroacetone extraction of technetium