Quaternary ammonium isobaric tag for a relative and absolute quantification of peptides

In the ongoing quest to develop improved quantitative approaches for complex mixtures of proteins, this month Setner and colleagues describe a strategy that combines an isobaric tag for relative and absolute quantification with the incorporation of a quaternary ammonium group to increase ionization efficiency. This strategy ‐ they call QAS‐iTRAQ 2‐plex ‐ can be adopted for both relative and absolute quantification of peptides. The authors provide an abundance of data in support of their approach, and describe its application to a series of model peptides and a tryptic digest of bovine serum albumin.