for screening of AA-BAs in positive and negative ion conditions. The precursor ions of the AA-BAs were set as [M+H] + and [M-H] -. The corresponding product ions were set as [M-nH2O+H] + and [M-nH2O-AA+H] + for positive ion mode and [AA-H] -for negative ion mode, respectively. MRM parameters were listed in Table .