Figure 2. Base-peak chromatogram of one of the 12 fractions separated by cation exchange chromatography and analyzed by LC-ESI-MS/MS with a nano-flow reverse-phase HPLC column, with gradient elution ranging from 5 to 50% solvent B in 40 min (A). Cation exchange chromatogram of the tryptic peptides derived from proteins associated with labial minor salivary gland secretion (Inset). MS/MS spectrum and sequence analysis of a tryptic peptide. The sequence of R.TVQIAAVVDVIR.E led to the identification of "prolactin inducible protein" (P12273). Matching b- and y-ion series are indicated in the upper right (B).