Determination of I-125 impurities in [I-123]labelled radiopharmaceuticals, by liquid scintillation counting: sensitivity of the method

Iodine-125 is a radioisotopic impurity "always" present in iodine-123, produced by nuclear reactions induced either. on natural or "highly" enriched targets. Liquid scintillation counting is a very sensitive tool to determine low level impurities of both low energy electrons and photons in aqueous and organic solutions of radiopharmaceutical compounds. With this technique it was possible to determine, on commercial samples, that the content of I-125 was of the order of not less than 0.1% for I-123 produced via I-127(p,5n) reactions and not less than 0.01% for I-123 produced via "highly" enriched Xe-124(p,X) nuclear reactions.