Quantity of Identified Metabolites in Untargeted Experiments

This is a difficult question to answer!

The CIT typically observes between 500 and 10,000 compounds, depending on sample type. It is important to note that there is a range of annotation confidences assigned to each detected compound. The CIT uses a classification system to describe annotation confidence. Briefly, more experimental evidence (e.g., diagnostic fragmentation data, retention time, collision cross section, reference standard, etc.) enables a higher confidence metabolite identification assignment. While some compounds can be unambiguously identified (Level 1), others may be reported in groups (multiple candidate annotations; Level 3) owing to the fact that numerous metabolites are isomeric and metabolite databases are inherently incomplete. We search our extensive in-house library to reduce the number of candidates and/or increase the confidence of candidates when possible.

This classification scheme is widely adopted by the metabolomics community, see 10.1007/s13361-016-1469-y for more information.