Electron transfer dissociation (ETD) is a tandem mass spectrometry fragmentation method used in research peptide analysis to break peptide backbone bonds by radical-driven chemistry while leaving many labile post-translational and synthetic modifications intact on the fragments. It complements collision-based fragmentation in the analytical laboratory.

How the method works: Multiply charged peptide cations react with reagent anions in the mass spectrometer; electron transfer induces N-Cα bond cleavage producing c- and z-type fragment ions. Reports should document precursor charge state, reagent and reaction time, supplemental activation settings, and calibration, because fragmentation efficiency depends strongly on charge density.

Use in a QC workflow: ETD is typically paired with HPLC purity testing, high-resolution accurate-mass measurement, and collision-based MS/MS, so sequence, modification site, identity, and purity findings are cross-checked by independent methods. It is especially informative for longer or highly charged peptides where collision methods give sparse coverage.

Limitations: ETD is inefficient for low-charge precursors and does not replace HPLC purity testing or accurate-mass identity confirmation; it supports those methods for fragmentation questions they answer less completely.

Disclaimer: For laboratory research purposes only. Not for human consumption. The methods described are analytical laboratory techniques; no medical or therapeutic claim is made.

Citations: Standard ETD tandem-MS methods literature for peptide sequencing and modification mapping.