Absolute and Accurate Quantification of Protein Phosphorylation by Using an Elemental Phosphorus Standard and Element Mass Spectrometry

The simpler the better: The combination of element mass spectrometry under optimized conditions and an elemental phosphorus standard provides a generic approach for absolute quantitative phosphoproteomics. This approach allows for simultaneous and reliable quantification of each individual phosphopeptide (corresponding to the different phosphorylation sites) present in a tryptic digest of a protein mixture.