Immunogenicity related to the degradation of therapeutic monoclonal antibodies (mAbs) remains a major concern for their therapeutic efficacy and safety. Therefore, an analytical method allowing characterization and detection of mAbs degradation is mandatory. In this study, a simultaneous coupling of size exclusion chromatography (SEC) to native mass spectrometry (MS) and fluorescence detection (FLD) is proposed to detect degraded therapeutic mAbs and biases of structural changes (e.g. dimerization, denaturation) that may occur during native MS. A comprehensive study on infliximab behaviors have been performed under different mobile phase conditions (e.g. composition, pH, organic solvent, etc.) and MS parameters (e.g. gas temperatures, CID energies, etc.). Experimental conditions avoiding artificial denaturation and/ or dimerization have been defined. We have also demonstrated that under the developed conditions infliximab affinity towards its biological target TNFα is preserved. In addition, using this method dimers, denatured monomers and fragments could be detected in trastuzmab samples stressed by a long-term storage. These results were confirmed by using SEC coupled to ion mobility mass spectrometry as an orthogonal method for the detection of denatured monomer.