Fractionation of phosphopeptides using reversed phase microcolumn prior to LC-MS analysis

A protocol for an improved phosphopeptide identification in tryptically digested complex peptide samples is described. The common TiO2 based phoshopeptide enrichment is coupled to a simple peptide fractionation protocol with following LC-MS analysis of the obtained fractions and proteomic identification of phosphorylated peptides. The fractions are obtained by an optimized protocol for peptide fractionation using a home-made capillary column coupled to a microgradient elution using a gastight microsyringe. The protocol leads to a substantially increased number of phosphopeptides (more than twice).