Determination of 125I impurities in [123I]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 125I was of the order of not less than 0.1% for 123I produced via 127I(p,5n) reactions and not less than 0.01% for 123I produced via 'highly' enriched 124Xe(p,X) nuclear reactions