Fig. 7.

There are two primary approaches used for quantitative proteomics: stable isotope labeling methods and label-free approaches. Isotopic labeling relies on the chemical labeling of the peptidome using stable isotope variants of the same reagent. Analysis of the MS for each peptide should reveal a heavy and light labeled version of the peptide and the ratio of these peptides enables quantitation. By contrast, in label-free approaches samples are run sequentially and the peak intensities are used to determine changes in the concentration of the peptide between two samples.