We employ stable isotope labeling of amino acids in cell culture (SILAC) to identify and quantify Lys and Arg post-translational modifications (PTMs) using QuARKMod. This approach allows us to take a global view of the PTM landscape following treatment. Using the consistent fragmentation observed with Lys and Arg residues, regardless of the PTM present, we can perform product ion scanning to view all PTMs. By matching retention times and comparing fragment ions, we can identify novel Lys and Arg PTMs. Our lab is focussed on describing the biological role of novel PTMs both in vitro and in vivo.