Figure 5.

Selected reaction monitoring (SRM) pipeline. In a typical SRM experiment, a triple quadrupole instrument is used. Here, the first and third mass analyzers, also known as Q1 and Q3, respectively, function as ion filters, selecting only the analytes with a specific m/z value at a predetermined retention time. The second quadrupole (Q2), in its turn, works as a collision cell to fragment the parent ions selected in the Q1. In this strategy, quantification per-se is obtained through the peak area ratios of the transition ions from an endogenous peptide and a reference analog.