Table 7 Communicating confidence in NTS via HRMS; text from original article with additional comments
From: NORMAN guidance on suspect and non-target screening in environmental monitoring
Identification confidence | Minimum requirements | Comments/observations |
|---|---|---|
Level 1: Confirmed structure by reference standard | MS, MS2, RT, Reference standard | For low intensity targets (no MS2), MS, RT and standard are sufficient, with lower IP |
Level 2a: Probable structure by library spectrum match | MS, MS2, Library or literature MS2 | High match values and sufficient fragments required, see Sect. “Spectral library search”) |
Level 2b: Probable structure by diagnostic evidence | MS, MS2, experimental data/context | Very rare case, often with clear parent–TP relationship |
Level 3: Tentative candidate(s) | MS, MS2, experimental data/context | Most identifications remain at this level. Defining study-specific sublevels can be helpful in reports |
Level 4: Unequivocal molecular formula | MS isotope/adduct (MS2 is helpful) | Many vendor approaches report formulas that are not unequivocal. See main text |
Level 5: Exact mass of interest | MS | “Of interest” implies that this mass has been prioritised, see Sect. “Prioritisation procedures in NTS” |