ia ▁or ▁water . ▁ ▁In ▁electron ▁transfer ▁dis soci ation ▁( ET D ) ▁and ▁electron ▁capture ▁dis soci ation ▁( E CD ), ▁the ▁pre domin ant ▁ ions ▁are ▁c , ▁y , ▁z + 1 , ▁z + 2 ▁and ▁sometimes ▁w ▁ ions . ▁ ▁For ▁post ▁source ▁decay ▁( PS D ) ▁in ▁M AL DI , ▁a , ▁b , ▁y - ions ▁are ▁most ▁common ▁product ▁ ions . ▁ ▁Fact ors ▁affect ing ▁fragment ation ▁are ▁the ▁charge ▁state ▁( the ▁higher ▁charge ▁state , ▁the ▁less ▁energy ▁is ▁needed ▁for ▁fragment ation ), ▁mass ▁of ▁the ▁pe pt ide ▁( the ▁larger ▁mass , ▁the ▁more ▁energy ▁is ▁required ), ▁induced ▁energy ▁( high er ▁energy ▁leads ▁to ▁more ▁fragment ation ), ▁primary ▁am ino ▁acid ▁sequence , ▁mode ▁of ▁dis soci ation ▁and ▁collision ▁gas . ▁ ▁Gu idel ines ▁for ▁interpretation ▁ ▁For ▁interpretation , ▁first , ▁look ▁for ▁single ▁am ino ▁acid ▁im mon ium ▁ ions ▁( H 2 N += CH R 2 ). ▁Cor respond ing ▁im mon ium ▁ ions ▁for ▁am ino ▁ac ids ▁are ▁listed ▁in ▁Table ▁ 1 . ▁Ign ore ▁a ▁few ▁pe aks ▁at ▁the ▁high - mass ▁end ▁of ▁the ▁spectrum . ▁They ▁are ▁ ions ▁that ▁under go ▁neutral ▁mole cules ▁losses ▁( H 2 O , ▁N H 3 , ▁CO 2 , ▁H CO OH ) ▁from ▁[ M + H ]+ ▁ ions . ▁Find ▁mass