There is disclosed a process for minimally derivatizing a targeting protein with a radionuclide such that the predominant species of derivatized targeting protein contains one radionuclide group as a single radiolabeled ligand, and whereby the binding characteristics of the targeting protein are minimally affected. There is further disclosed ligands that can chelate a metal radionuclide or bind a halogen radionuclide while providing a means for separating radiolabeled ligand from unradiolabeled ligand.