Waters Corporation 1 article published in JoVE Chemistry An HS-MRM Assay for the Quantification of Host-cell Proteins in Protein Biopharmaceuticals by Liquid Chromatography Ion Mobility QTOF Mass Spectrometry Catalin Doneanu*1, Jing Fang*1, Yun Alelyunas*1, Ying Qing Yu1, Mark Wrona1, Weibin Chen1 1Waters Corporation Here, we describe a chromatographic assay coupled with the ion mobility separation of peptide precursors followed by the high-resolution (~30,000) MS-detection of peptide fragments for the quantification of spiked peptide standards in a monoclonal antibody digest.