All reaction steps are typically carried out at 4??? C. Where the Ligand is a monoclonal antibody having one or more disulfide bonds, solutions of the monoclonal antibody (5-20 mg/mL) in phosphate buffered saline, pH 7.2, are reduced with dithiothreitol (10 mM final) at 37??? C. for 30 minutes (See General Procedure M) and separation of low molecular weight agents is achieved by size exclusion chr