Figure 1.

Schematic diagram of the isobaric carrier concept. The peptides from small samples and from a larger (carrier) sample are labeled with isobaric tags, mixed, and analyzed by MS/MS. Some sets, as the standards listed in Table 1, may have more than one isobaric carrier sample. This approach increases the intensity of precursor ions (1), provides RIs for quantification (2), and facilitates sequence identifications based on the peptide fragments pooled across all samples (3).