Fig. 5From: Accurate and efficient amino acid analysis for protein quantification using hydrophilic interaction chromatography coupled tandem mass spectrometryOverlap in mass ranges, M0 − Mn, where n is the maximum number of 13C and 15N isotopologues possible for each amino acid. The inset figures indicate separation of amino acids with overlapping masses that can be resolved by HILIC and used to quantify isotopologues. *Cysteine was measured as cystineBack to article page