The Proposed Identification Hierarchya
| Information Content | Information Type | Information Example | Title | Reporting Example |
|---|---|---|---|---|
| Insufficient information to propose a structure or identity | Chromatographic and/or spectroscopic data that provide little or no insight into the possible structure or identity | 1. GC/FID peak with no GC/MS peak. 2. GC/MS peak with no library hits and uninterpretable spectra. 3. LC/UV peak with no MS signal. 4. LC/MS peak with uninterpretable spectra. | Unidentified | Unidentified |
| Sufficient information to propose a structure but insufficient information to propose a specific identity | Chromatographic and/or spectroscopic data that are sufficient to infer a general structure but not sufficient to propose a specific identity | 1. Peak with GC/MS or LC/MS spectrum that can be interpreted sufficiently that a structure can be inferred. 2. Structure is inferred by reference to internal/external literature. 3. Accurate mass MS that infers the empirical formula only. | Partial | A phthalate (e.g., di-(2-ethylhexyl) phthalate) |
| Sufficient information to propose a specific identity | Chromatographic and/or spectroscopic data that are sufficient to infer a specific identity; however, additional data do not exist to support the identity (one dimension) | One-dimensional information that is one of the following: 1. GC/MS peak with library spectral match. 2. LC/MS peak with definitive molecular weight and match to an equivalent molecular weight in a GC/MS peak. 3. GC/MS or LC/MS peak whose structure has been elucidated by expert interpretation of the mass spectrum. | Tentative (interpretative or matching) | Di-(2-ethylhexyl) phthalate, tentative |
| Sufficient information to support a proposed specific identity | Chromatographic and/or spectroscopic data that are sufficient to infer a specific identity; inference is supported by additional data (two dimensions). | Two-dimensional information that includes the following pairs: 1. GC/MS peak with library spectral match or LC/MS peak with definitive molecular weight and match to an equivalent molecular weight in a GC/MS plus retention time match. 2. GC/MS peak with library spectral match or LC/MS peak with definitive molecular weight and match to an equivalent molecular weight in a GC/MS plus accurate mass. 3. GC/MS peak with library spectral match or LC/MS peak with definitive molecular weight and match to an equivalent molecular weight in a GC/MS plus MS/MS fragment pattern interpretation. 4. GC/MS peak with library spectral match or LC/MS peak with definitive molecular weight and match to an equivalent molecular weight via GC/MS plus inference from internal or external literature. 5. GC/MS peak with library spectral match or LC/MS peak with definitive molecular weight and match to an equivalent molecular weight in a GC/MS plus inference from NMR. 6. The same identity is proposed by orthogonal analytical methods (e.g., both GC/MS plus LC/MS) independently. | Confident | Di-(2-ethylhexyl) phthalate, confident |
| Sufficient information to confirm a specific identity | Chromatographic and/or spectroscopic data that are sufficient to infer a specific identity; inference is supported either by comparison to an authentic reference standard of the inferred substance or a preponderance of supporting data (three or more dimensions). | Retention time and spectral match to an authentic reference standard. Three-dimensional information including three or more collaborating pieces of information (e.g., GC/MS spectral match, LC/MS spectral match, GC/MS and LC/MS accurate mass-provided chemical formulas) | Confirmed (data-based or standard-based) | Di-(2-ethylhexyl) phthalate, confirmed |
In this Table, the term “or” refers to two pieces of information, either of which serves, in the absence of the other, as the basis of an identification, The term “plus” means two independent pieces of information which both separately and collaboratively support the same identity.
↵a The type of data required for an identity to fall within a given category is given, and the use of that information to establish an identity is illustrated using an example compound, di-(2-ethylhexyl) phthalate.