Methionine oxidation is considered a critical quality attribute (CQA) of therapeutic antibodies and may impact the clinical safety and efficacy of the final drug product. Therefore, monitoring of methionine oxidations is required during the discovery, development, and production of therapeutic antibodies. Traditional methods to characterize oxidation rely on tryptic peptide mapping and LC-MS, a labor intensive and time-consuming process that generates large data sets and requires trained and skilled manual interpretations. Middle-level analysis provides a faster and simpler alternative by combining minimal sample preparation with short analysis time. It entails the digestion of the mAb at one specific site below the hinge using the FabRICATOR protease which – after reduction of disulfide bonds – yields three subunits of 23-25 kDa in size. These are well suited for analysis by LC-MS for the quantification of many different CQAs. Here, we present a rapid LC-MS assay for antibody oxidation analysis at the middle level. It is based on a 30 minute one-pot digestion/reduction using and FabRICATOR and GlycINATOR followed by reverse-phase LC-MS on a Waters BioAccord system with a run time of only 15 minutes per sample. All sample preparations were performed in an automated fashion using an Andrew+ liquid handling robot (Waters). Using this assay, we were able to reliably quantify methionine oxidation in a panel of different commercial mAb that had undergone forced oxidation. No method optimization was necessary to run mAbs of different subclasses, making this a platform method applicable to many different samples. The short analysis time, simple data interpretation and the possibility for automation of sample preparation make this assay ideally suited for high volume applications such as stability studies or formulation optimization.