Figure 3 - Stages of incorporation of stable isotope labels and their impact on quantitative accuracy.

The scheme outlines typical labeling workflows in quantitative proteomics from the cell or tissue stage through purification and protein digestion to MS analysis. The blue and the yellow boxes represent the two cell states to be differentially labeled and compared. The horizontal line denotes the stage where samples are combined. When samples have to be processed in parallel, uncompensated quantification errors can occur (dashed lines).