Modern therapeutic approaches, especially for cancer and certain autoimmune disorders, evolved and have started to frequently rely on monoclonal antibodies (mAb) or other recombinantly prepared biomolecules (biopharmaceuticals) instead of on small molecules. The mAb treatment is effective but comes at a high financial cost. That is why there is a high demand to develop and market so-called ‘biosimilars’, which are highly similar to already approved biopharmaceuticals.The major hindrance for biosimilars manufacturers is that they must declare and prove an almost identical structure, biological activity, quality, safety and efficacy that apply to the original innovator molecule. To prove structural identity, it’s necessary to characterize not only primary sequences and post-translational modification of expressed proteins but also proper protein folding, and any chemical modifications introduced by production, purification and long-term storage. To determine higher order structure of antibodies, a broad palette of techniques can be considered. In this project we used recently discovered fast fluor-alkylation of proteins (FFAP) that offers another approach for structural characterization of therapeutic antibodies and identifying epitope-paratope interacting regions.