Tandem Mass Analysis

Tandem MS entails multiple rounds of mass analysis. Thus tandem MS instruments are capable of ion isolation and fragmentation and mass analysis of fragment ions. Fragmentation can be achieved in several ways including collision-induced dissociation (CID), electron capture dissociation (ECD), and electron transfer dissociation (ETD). Fragmentation of the parent ion generates daughter ions that can be used to determine the amino acid sequences of peptides, and characterize post-trans-lational modifications of proteins. The most common fragmentation method used in proteomics is CID. Peptide ions analyzed in an initial mass analyzer are directed into a collision cell where individual ions can be isolated and fragmented by collision with an inert gas (helium). Fragment ions exit the collision cell and are separated in a second mass analyzer before scanning out to the detector. The fragmentation pattern of peptide ions by CID occurs along the peptide backbone and yields a fairly predictable array of ions. The resulting m/z data from the original precursor ion and the fragmentation data from product ions can be used to determine the peptide sequence.

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