The present invention relates to trifunctional crosslinking reagents carrying (i) a ligand-reactive group for conjugation to a ligand of interest having at least one binding site on a target glycoprotein receptor, (ii) an optionally protected aromatic hydrazine group for the capturing of oxidized receptor-glycopeptides and (iii) an affinity group for the detection, isolation and purification of captured glycopeptides, their methods of production, as well as their use in methods for detecting, identifying and characterizing interactions between ligands and their corresponding glycoprotein target receptors on living cells and in biological fluids.