Differential solubility labelling and purification of ortho-iodo-hippuric acid with 123I

A simple method is described for the production of high quality clinical 123I hippuran at TRIUMF. The first feature is that solid ortho-iodo-hippuric acid (IHA) is heated with aqueous [123I]iodide creating a single phase where labelling occurs. When subsequently cooled to room temperature, IHA crystallizes. The second feature is employed at this stage. A density gradient is created with NaCl to remove the supernatant fluid from the IHA crystals. The IHA is then neutralized for pharmaceutical use. The product purity is consistently >99% by TLC and by HPLC analysis that is described. The initial tag is typically 96% and the useful recovery is 85% by this process. Iodine-123 has been used up to 100 mCi per batch from the 500 MeV 133Cs (p,2p,9n) 123Xe reaction and from the 124Xe (p,2n) 123Xe reaction. (author)