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  • Author or Editor: M. Kohličková x
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Abstract  

The effect of the pH of the aqueous phase on the sorption of134Cs,85Sr,125I and99Tc radionuclides has been investigated. Different types of bentonites from north-western Bohemia 85 in mixture with quartz sand have been used for the experiments with134Cs and85Sr. ThK d values have been determined using a batch method. The effect of the redox potential Eh on the sorption of radionuclides and the speciation of radionuclides125I and99Tc has also been investigated. Polarography has been used for speciation of the radionuclides.

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Abstract  

The conditions for the synthesis of rhenium compounds (pH, reaction time, concentration of reducing agent) have been determined previously by thin-layer chromatography. A Britton-Robinson buffer solution has been selected as a carrier electrolyte due to its possible use in a wide interval of pH, mainly at optimal pH for the formation of the complexes studied. The same electrolyte has been previously applied also in case of the study of rhenium and technetium complexes by polarography. The electrophoretic experiments have been carried out under both standard and reverse polarities with direct UV detection at the wavelength 214 nm and 20 °C. The signal of perrhenate has been observed at the reverse polarity (outlet+, inlet–), of reduced rhenium [probably Re(IV)] under normal polarity. The formation of rhenium complexes with EDTA has been shown by lowering of the cationic rhenium signal due to the addition of the ligand. The rhenium complexes with EDTA are observable at reverse mode of CE. The formation of rhenium complexes with HEDP (hydroxyethylidenediphosphonic acid) has been studied in two different carrier electrolytes — 40 mM Britton-Robinson buffer solution and 50 mM phosphate buffer with 20 mM HEDP. The mechanism of perrhenate reduction by stannous chloride and of the formation of rhenium complexes with EDTA has been determined. The necessity of the presence of ascorbic acid as an antioxidant in the reaction mixture at different pH values has been described as well.

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Abstract  

Thin-layer and paper chromatography have been used for the determination of radiochemical yields of186Re complexation with three selected ligands methylenediphosphonic acid (MDP), ethylenediamminotetraacetic acid (EDTA), and citrate convenient for the radiopharmaceutical applications. The combination of selected two chromatographic systems has been chosen due to the satisfactory separation of free perrhenate, corresponding complex with186Re and reduced hydrolyzed rhenium. Rhenium complexes with studied ligands were prepared by reduction of perrhenate at presence of suitable ligand. Stannous chloride together with ascorbic acid (antioxidant) was used for perrhenate reduction. The effect of pH of reaction mixture, reaction time and concentration of reducing agent on the radiochemical yield of complexation is described and the optimal conditions for synthesis of rhenium complexes with MDP, EDTA and citrate have been found. Under optimal condition the radiochemical yield of complexation186Re-MDP,186Re-EDTA and186Re-citrate reached more than 90%, 80%, and 80%, respectively.

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Abstract  

A large group of radiopharmaceuticals includes complex radionuclide-ligand compounds which are very sensitive to the preparation conditions, as for example pH of reaction mixture, incubation time, temperature, molar ratio of reagents, etc. It is necessary to find the optimum condition for the formation of the radionuclide-ligand complex and to select the convenient analytical methods to determine the purity of the product. The preparation of radiopharmaceuticals labeled by rhenium-186 or rhenium-188 requires the addition of a reducing agent (commonly stannous chloride) to the reaction mixture in order to reduce perrhenate to a lower oxidation state which is capable of complex formation. For rhenium concentration up to approximately 10-5 mol/l, the molar excess of reduction agent over perrhenate is usually higher than 800 to reach the optimum yield of reduction and complexation (between 80-95%). Because of the potentially toxic effect of SnCl2 the reduction of perrhenate by stannous chloride was studied in detail to find the way for decreasing the concentration of reducing agent in the reaction mixture without significant lowering of the yield of perrhenate reduction. The reduction of perrhenate was determined by electromigration methods, i.e., capillary electrophoresis (CZE) and isotachophoresis (ITP), and thin-layer chromatography (TLC) with radiometric detection. The highest degree of reduction of perrhenate was obtained at pH 2 at perrhenate concentration ranging from 10-4 to 10-3 mol/l. The stability of reduced rhenium against a pH change from 2 to 5.5 (which corresponds to the pH close to physiological values) was tested as well. The influence of the presence of ascorbic acid as an antioxidant in the reaction mixture on the stability of the preparation against the pH change was determined. The stability of reduced rhenium against dilution of rhenium in the reaction mixture to the concentration suitable for the application in radiotherapy was also found out. The data acquired by capillary electrophoresis, isotachophoresis and thin-layer chromatography are comparable. Results obtained in these experiments were applied for the study of rhenium complexes with hydroxyethylidenediphosphonic acid (HEDP).

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Abstract  

The reaction conditions for synthesis of three rhenium complexes 186Re-methylendiphosphonate (MDP), 186Re-hydroxyethylidendiphosphonate (HEDP) and 186Re-citrate were investigated. Radiochemical yield of complexation was determined by thin-layer chromatography and paper chromatography. The rhenium complexation with corresponding ligand was dependent on pH values of reaction mixture, concentration of the ligand studied (MDP, HEDP and sodium citrate) and concentration of the reducing agent. Stannous chloride with ascorbic acid (as antioxidant) was used for reduction of perrhenate. The labeling yield was about 90% for 186Re-MDP, more than 80% for 186Re-HEDP and more than 75% for 186Re-citrate under optimum conditions. The possibility of application of porphyrines as organic ligands for complexation with rhenium isotopes was also examined.

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