Multiple reaction monitoring (MRM) scans were performed for each standard by selecting the protonated molecular ion [M + H]+1 (parent ion) with the first mass filter quadrupole (Q1). The product ions, yielded by collision-induced dissociation, were scanned by the third quadrupole (Q3). Unambiguous Q1/Q3 pair transitions were obtained by manually optimizing the declustering potential to get characteristic product ions of ANTX and PHE (Table (Table2).2).