Electron transfer dissociation

Electron transfer dissociation (ETD) is a method to fragment ions in a mass spectrometer. Similar to electron capture dissociation, ETD induces fragmentation of cations (e.g. peptides or proteins) by transferring electrons to them.

ETD fragmentation
ETD does not use free electrons but employs radical anions (e.g. anthracene or azobenzene) for this purpose:


 * $$[M + nH]^{n+} + A^- \to \bigg[ [M + nH]^{(n-1)+} \bigg]^* + A \to fragments$$.

ETD cleaves randomly along the peptide backbone (so called c and z ions) while side chains and modifications such as phosphorylation are left intact. The technique only works well for higher charge state ions (z>2), however relative to collision-induced dissociation (CID), ETD is advantageous for the fragmentation of longer peptides or even entire proteins. This makes the technique important for top-down proteomics.