Figure 1.

Illustrative iceberg representation of high dynamic range of proteins found in blood, showing various classes of proteins and peptides (figure composed of literature data [21] and others). Four arbitrary assemblies of proteins/peptides can be made, and representative species are indicated. Iceberg tip contains abundant classical plasma proteins detectable in 1 μL of sample or less. Tissue leakage proteins typically require, at least, 1 mL plasma volumes (typically after depletion of interfering abundant proteins), and concentration ranges of secreted signal peptides/proteins like insulin, somatotropin are yet another 3 orders of magnitude lower. Interleukins and other cytokines really push current MS systems to their very limit, whereas other neurosecretory signal peptides require extensive concentration steps to reach levels detectable by MS.