Schematic representation of phosphoprotein analysis workflow. The most commonly used methods to resolve, to purify or to enrich phosphoproteins are described in the Protein separation section. Peptides resulting from trypsin digestion of phosphoproteins may be analyzed directly by MS or by Edman degradation. Other approaches may be used for the enrichment of phosphopeptides. These methods are depicted in the Peptide separation section. MALDI and ESI are usually used for identification of phosphoproteins. The two predominant techniques for idenditification of the precise sites of phosphorylation are i) Edman degradation and ii) MS analysis (Neutral loss and Precursor ion). These methods are described in the Identification section. 1D/2D GE: On-dimensional/Two-dimensional gel electrophoresis. Chem. Modif.: Chemical Modification. ESI: Electrospray Ionisation. Ib: Immunoblot. IMAC: Immobilized Metal Affinity Chromatography. Ip-α PY: Immunopurification using a phospho-tyrosine antibody. LC: Liquid Chromatography. MALDI: Matrix-Assisted Laser Desorption Ionization. ProQ: Pro-Q Diamond™. AR: Autoradiography. β-Elemin: β-elimination reaction.