Figure 8.

Chemical structure of isotopic reagents, light TMT and heavy TMT, used for targeted quantification.¹¹¹ The light reagent has no heavy isotope incorporated, whereas the heavy reagent has five heavy isotopes incorporated (4 × ¹³C and 1 × ¹⁵N). Labeling with these reagents introduces mass differences into the peptides from different samples. In targeted experiments, quantification is obtained by structural b and/or y ions generated after collision-induced dissociation.