derives from O-phospho-L-serine O-phospho-L-serine with neutral loss of phosphate -97.976898193359375 -98.0 69.02146148681640625 69.05999755859375 H -3 O -4 P -1 PSI-MOD none C 3 H 3 N 1 O 1 MOD:00435 Covalent modification of a peptide or protein amino acid phosphorylated serine with a secondary loss of a neutral trihydrogen phosphate molecular fragment. dPhosOPhosSer MOD:00046 artifact phosphorylated residue with neutral loss of phosphate