Figure 1. Targeted enrichment and quantitation using an immuno-SRM assay.

The sample can be a variety of complex proteomic samples. To achieve quantitation of the targeted protein(s), these larger molecules are digested to component peptides using an enzyme such as trypsin. A stable isotope standard (SIS) is added to the sample at a known concentration for quantitative analysis. The selected peptides are then enriched using anti-peptide antibodies immobilized on a solid support. Following washing and elution from the anti-peptide antibody, the amount of surrogate peptide is measured relative to the stable isotope standard using targeted mass spectrometry.