Strategy for the enrichment of oxPL-modified peptides using C18 columns. (1) Proteolytic digestion of oxPL–protein adducts to generate oxPL-modified peptides, (2) enrichment using a C18 column to remove hydrophilic unmodified peptides and other interfering compounds, (3) aminolysis to transform oxPL-modified peptides into hydrophilic PLEAs, (4) enrichment using a C18 column to separate PLEAs from other interfering hydrophobic unmodified peptides and compounds, (5) peptide analysis by LC-MS/MS, and (6) peptide identification.