A chemical ''hub'' for absolute quantification of a targeted protein: orthogonal integration of elemental and molecular mass spectrometry

A novel element-tagged activity-based photo-cleavable biotinylated chemical ``Hub'' was designed and synthesized to orthogonally integrate ICP-MS and ESI-MS for absolute targeted-protein quantification. This tetrafunctional chemical ``hub'' allowed us to quantify a targeted protein using species-unspecific isotope dilution ICP-MS and to know which protein is being quantified using ESI-IT-MS at the same time.