Studies on (−)ESI-MS/MS of a glycosaminoglycan disaccharide N-acetyllactosamine-6,6′-disulfate disodium salt-Charge-localization isomers

► Charge-localization isomers possible for a dibasic acid negative precursor ion. ► Unusual migration of sulfate anion from a sugar unit to the next unit. ► Usefulness of accurate mass measurement to determine the fragmentation path.