Monoclonal antibodies (mAbs) are indispensable in the therapeutic arsenal, particularly in oncology and auto-immune diseases. Due to its biological origin, a mAb-based drug represents a heterogeneous mixture of several variants, that result from its biological production method. Some variants can potentially influence quality of final drug product and are defined as critical quality of attributes (CQAs). To be able to ensure the efficacy, the safety and the quality of drugs, a rigorous control must be carried out. This thesis work is a part of a quality approach through research and development of new analytical methods. The goal is to ensure that the therapeutic proteins do not contain any CQAs, that could potentially affect the patient health. Therefore, liquid chromatographic (LC) methods and their potential hyphenation to mass spectrometry (MS) for therapeutic protein analytical characterization have been deeply studied. The major achievement accomplished during the thesis are presented in this manuscript.