“Identity confirmed” can summarise very different amounts of evidence. Before deciding whether such a statement meets a study's needs, define the identity question precisely. The important issue is whether the evidence discriminates the intended material from the alternatives that would change the experiment's interpretation.
Define the candidate at the required level
Write the intended sequence and the structural qualifications relevant to the study. These may include a terminal modification, an attached group, a defined complex or another feature. A short name can be a useful label, but it should point to that fuller definition.
Then state the alternatives that matter. For an original hypothetical experiment comparing ALA with AIA, the middle residue distinguishes the candidates. In another study, the decisive distinction might be an unmodified versus modified end. These questions need not be resolved by the same evidence.
Map each distinction to the observation needed
| Question | Evidence to investigate | Shortcut to avoid |
|---|---|---|
| Does the mass agree with the candidate? | Assigned ion, mass basis, comparison and tolerance | Treating an unlabelled peak as a neutral molecular mass |
| Is residue order supported? | Relevant sequence or fragment evidence | Assuming intact mass uniquely specifies order |
| Is a modification established? | Evidence that discriminates modified from unmodified material | Inferring the modification from the product name alone |
| Are isomeric alternatives distinguished? | A method capable of resolving the particular alternatives | Assuming more mass decimal places solve every ambiguity |
This table is a planning aid, not a prescribed test panel. The study team and analytical specialists need to determine which procedures are suitable. Its purpose is to make the logical connection visible between a structural question and the evidence expected to answer it.
ICH's analytical-validation guidance addresses specificity and selectivity and recognises that supporting procedures may be needed when one procedure does not supply enough discrimination. The relevant capability is therefore tied to the intended measurement and its potential interferences.ICH analytical selectivity (opens in a new tab)
Ask what sits behind the certificate summary
A certificate may report “conforms” against an identity reference without displaying the full supporting data. That summary can be recorded as the laboratory's conclusion. If the research question depends on a finer distinction, request the relevant criteria and evidence rather than assuming the summary establishes it.
Useful questions include which reference was used, what feature was compared, which acceptance criteria applied and what ambiguity the method leaves. Ask for information relevant to the decision; a large raw-data file without an understandable assignment may still leave the central question unanswered.
Keep provenance separate too. Evidence that a procedure can distinguish two candidates does not establish that a particular PDF is authentic. Document verification and analytical discrimination are both useful checks, but one cannot substitute for the other.
Avoid both underclaiming and overclaiming
For the hypothetical ALA/AIA comparison, intact mass alone leaves both candidates possible when the remaining chemistry matches. It would be too strong to claim that the middle residue was confirmed from that observation. It would also be too strong to say the mass result contributes no information at all: it still constrains the material description.
A proportionate conclusion states what is supported and what remains open. The study's decision can then address the unresolved distinction explicitly. This is more useful than a universal rule that one named technique is always sufficient or that every reagent requires the same exhaustive package.
Nature's guidance for new biomolecular materials calls for sequence-based information where appropriate and mass-spectral characterisation. Its scope illustrates that identity support can involve complementary evidence; it should not be converted into a universal purchasing rule for all existing reagents.Nature characterisation guidance (opens in a new tab)
Document the requirement before using the result
- Candidate definition and relevant alternatives.
- The observations expected to distinguish them.
- Available method details, references and assignments.
- Unresolved alternatives and their importance to the study.
- The resulting suitability decision and its rationale.
An identity requirement is successful when a later reader can see why the evidence was considered sufficient for the specific comparison. It should expose the assumptions on which the interpretation rests, not hide them behind a general assurance.
Sources and further detail
- ICH — Q2(R2): Validation of analytical procedures (opens in a new tab)
Section 3.1 on specificity/selectivity and use of supporting procedures where needed. Does not validate a particular supplier's assay.
- Nature — Characterisation of chemical materials (opens in a new tab)
November 2017 chemistry guidance; distinguishes identity, purity and sufficient experimental description. A journal standard for reported work, not a universal procurement specification.
Sources checked 19 September 2026. Worked examples are illustrative unless a supplied report is explicitly identified. This article has not undergone independent scientific peer review.