▁( y - 1 7 ) ▁or ▁( b - 1 7 ) ▁ ions ▁with ▁higher ▁abund ance ▁than ▁their ▁corresponding ▁ ions . ▁ ▁When ▁C - ter minus ▁has ▁a ▁basic ▁resid ue , ▁the ▁pe pt ide ▁generates ▁( bn - 1 + 1 8 ) ▁ion . ▁ ▁A ▁complement ary ▁b - y ▁ion ▁pair ▁can ▁be ▁observed ▁in ▁multiply ▁charged ▁ ions ▁spect ra . ▁For ▁this ▁b - y ▁ion ▁pair , ▁the ▁sum ▁of ▁their ▁sub scripts ▁is ▁equal ▁to ▁the ▁total ▁number ▁of ▁am ino ▁acid ▁resid ues ▁in ▁the ▁unknown ▁pe pt ide . ▁ ▁If ▁the ▁C - ter minus ▁is ▁Arg ▁or ▁L ys , ▁y 1 - ion ▁can ▁be ▁found ▁in ▁the ▁spectrum ▁to ▁prove ▁it . ▁ ▁Method s ▁for ▁pe pt ide ▁fragment ation ▁In ▁low ▁energy ▁collision ▁induced ▁dis soci ation ▁( C ID ), ▁b - ▁and ▁y - ions ▁are ▁the ▁main ▁product ▁ ions . ▁In ▁addition , ▁loss ▁of ▁am mon ia ▁(- 1 7 ▁Da ) ▁is ▁observed ▁in ▁fragment ▁with ▁R K N Q ▁am ino ▁ac ids ▁in ▁it . ▁L oss ▁of ▁water ▁(- 1 8 ▁Da ) ▁can ▁be ▁observed ▁in ▁fragment ▁with ▁ST ED ▁am ino ▁ac ids ▁in ▁it . ▁No ▁satellite ▁ ions ▁are ▁shown ▁in ▁the ▁spect ra . ▁ ▁In ▁high ▁energy ▁C ID , ▁all ▁different ▁types ▁of ▁fragment ▁ ions ▁can ▁be ▁observed ▁but ▁no ▁losses ▁of ▁am mon