Abstract
AbstractFree‐ion selective radiotracer extraction (FISRE) is a technique combining ion exchange and the use of radiotracers in order to determine labilities of metal complexes. The aminocarboxylate chelates 90Y‐EDTA, 90Y‐DTPA as well as 90Y‐DOTATOC, a radiopharmaceutical for neuroendocrine tumor treatment have been studied by FISRE using Chelex cation exchanger within the pH range 5.0–7.4. Time‐dependent speciation and dissociation rate constants have been determined in a time frame of 0.6 s–648 h. As indicated by thermodynamic constants, the lability decreases significantly with higher ligand denticity, cyclic coordination and upon peptide coupling resulting in the lability order Y‐EDTA>Y‐DTPA>Y‐DOTA>Y‐DOTATOC. Besides, studies of the effects of the metal/ligand ratio on FISRE suggest that – in contrast to EDTA and DTPA – cyclic ligands DOTA and DOTATOC tend to shield the ion exchanger from free yttrium ions after complex dissociation even at slight excess of metal ions. Copyright © 2008 John Wiley & Sons, Ltd.
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