Method for preparing radionuclide-labeled chelating agent-ligand complexes

A method for preparing a radionuclide-labeled chelating agent-ligand complex comprising:

• (a) reacting an anionic chelating agent with excess cationic radionuclide in aqueous solution to form:
• (i) an electrically non-negative radionuclide chelate in aqueous solution;
• and,
• (ii) remaining free cationic radionuclide in aqueous solution,
• wherein said anionic chelating agent has a chelating group and at least one pendant linker group that is capable of covalently binding a ligand;
• (b) reacting an anionic quenching agent in aqueous solution with the remaining free cationic radionuclide of the aqueous reaction mixture of step (a) to form an anionic radionuclide-quenching agent chelate in aqueous solution;
• (c) purifying said electrically non-negative radionuclide chelate from the aqueous reaction mixture of step (b), and away from said anionic radionuclide-quenching agent chelate, wherein said purifying step consists essentially of filtering said reaction mixture through an anion exchange medium, whereby said anionic radionuclide-quenching agent chelate is bound and retained by said anion exchange medium while said electrically non-negative radionuclide chelate passes through said anion exchange medium, to yield purified electrically non-negative radionuclide chelate in aqueous solution;
• and
• (d) reacting said purified electrically non-negative radionuclide chelate of step (c) with said ligand in aqueous solution to form said complex in aqueous solution, wherein said at least one pendant linker group is covalently bound to said ligand.