An additional CQA that was identified via the iMAM SEC-MS analysis was the presence of a protein dimer . The self-association of proteins to form dimers are a common phenomenon. The formation of protein dimers can be a key factor in the regulation of proteins such ion channels, receptors and transcription factors . Hence dimer formation quantitation is a crucial CQA to monitor during the production process of biotherapeutic proteins. This CQA was identified during SEC-MS analysis and incorporated into the protein workbook. The relative abundance of the dimer present was consistent between the four DP batches and comparable to the DS reference sample, ranging from 2.84% to 3.91% (Figure ).