In some embodiments, the invention relates to methods for creating a monoclonal antibody that specifically binds to antigen. The method may start from a polyclonal population of antibodies such as a non-specific polyclonal population or a polyclonal population of antibodies that specifically bind to the antigen. The method includes obtaining nucleic acid molecules encoding heavy and light immunoglobulin chains (or variable regions thereof) of multiple immunoglobulins from an animal； obtaining mass spectra information of peptide fragments of a population of polyclonal immunoglobulins that specifically bind to an antigen of choice； comparing and/or correlating the mass spectra information of the peptide fragments of the polyclonal immunoglobulins with predicted mass spectra information of predicted amino acid sequences encoded by the nucleic acid molecules, and then assembling the heavy and light chains to create an antibody (or variable region thereof) that specifically binds to the antigen.
