Extracted LC-MS-MRM chromatogram of phenolic acids found in prickly pear. MRM transition are given in brackets: 1, protocatechuic (m/z 152.9 → 107.8); 2, caffeic (m/z 178.7 → 134.9); 3, syringic acid (m/z 196.9 → 122.8); 4, 4-hydroxy-benzoic (m/z 136.9 → 93); 5, salicylic (m/z 136.9 → 93); 6, gentisic (m/z 152.8 → 107.9); 7, trans-sinapic acid (m/z 222.8 → 148.9); 8, cis-sinapic acid (m/z 222.8 → 148.9); 9, p-coumaric (m/z 162.8 → 119); 10, m-coumaric (m/z 162.8 → 119); 11, ferulic (m/z 192.8 → 133.9); 12, isoferulic acid (m/z m/z 192.8 → 133.9); 13, 3,4-dimethoxycinnamic acid (m/z 206.8 → 147.9).