Isobaric tag for relative and absolute quantitation

[1][2][3] It uses stable isotope labeled molecules that can be covalent bonded to the N-terminus and side chain amines of proteins.

The ITRAQ method is based on the covalent labeling of the N-terminus and side chain amines of peptides from protein digestions with tags of varying mass.

[citation needed] These samples are then pooled and usually fractionated by liquid chromatography and analyzed by tandem mass spectrometry (MS/MS).

A database search is then performed using the fragmentation data to identify the labeled peptides and hence the corresponding proteins.

The fragmentation of the attached tag generates a low molecular mass reporter ion that can be used to relatively quantify the peptides and the proteins from which they originated.