Due to the generation of specific side chain fragments, ECD is – contrary to CID – able to differentiate between Leucine and Isoleucine. The ExD cell can produce side-chain fragmentation useful for distinguishing leucine from isoleucine residues. Isoleucine loses 29 Da to form a w ion, while leucine loses 43 to form a w-ion. This allows for unequivocal calling of the present amino acid.