Extraction of technetium-99m by some organic solvents from macro scale molybdenum solution.

Objectives Molybdenum-99(⁹⁹Mo)/Techtetium-99m(^99mTc) is generally produced by a nuclear reactor. We studied the method to obtain enough activity of ^99mTc for nuclear medicine using a cyclotron. In the previous work, we demonstrated that ^99mTc was extracted with methyl ethyl ketone (MEK) efficiently from the aqueous solution dissolved macro amount of MoO₃. However, it was found that the considerable amounts of Mo were contaminated into the organic phase. One of the reason is high dissolvability of MEK to water (29 g/100 mL water; 20°C). We examined the extraction of ^99mTc from the 99Mo/^99mTc aqueous solution with several organic solvents (ethyl acetate, diethyl ether, hexane, carbon tetrachloride, chloroform, dichloromethane). Further the contamination of Mo in the organic solvents was discussed.

Methods We selected some organic phases (ethyl acetate, diethyl ether, hexane, carbon tetrachloride, chloroform, dichloromethane). We prepared 500 mL of molybdenum stock solution (included 2 M NaOH and 167 g MoO₃). After extraction, the organic phases were evaporated and prepared to detect molybdenum concentration by ICP-AES. In the case of ^99mTc extraction experiment, we used the stock solution included 9 MBq of Na^99mTcO₄ solution. ^99mTc concentration was measured the organic phases by γ-counter. The ratio of aqueous and organic phases was 1:1, respectively.

Results The Mo concentrations of MEK and other organic phases were ca. 22 ppm and less than 2 ppm after extraction (2 ppm was limitation). ^99mTc yield was 0.84 in MEK, however its yields were less than 0.1 in other organic solvent. The yields were 0.066 in ethyl acetate, 0.051 in chloroform, 0.005 in carbon tetrachloride, 0.001 in dichloromethane, and less than 0.001 in hexane and diethyl ether.

Conclusions MEK is good extracting solvent to ^99mTc, however Mo is also included in extracted solvent. In the future, we have to optimize the method to remove Mo in MEK, or search the solvent which extracts ^99mTc efficiently and decreases mixing Mo quantity.