A peptide Certificate of Analysis (COA) is a batch-linked record of the analytical testing performed on a research compound. A useful COA should help answer five questions: what material was tested, which batch was tested, what methods were used, what those methods showed, and when the testing occurred.
Two points matter before reading any further. Identity and purity are not the same measurement — one asks "is this the compound it claims to be?" and the other asks "how much of the analysed material corresponds to the main peak?" A single high purity percentage does not, on its own, prove every quality attribute of a batch.
What is a peptide Certificate of Analysis?
A COA is an analytical report tied to a specific production batch or lot. It documents the tests a laboratory performed on a sample drawn from that batch and the results those tests returned. It is a record of measurement, not a marketing claim, and it is only meaningful when it can be traced back to the exact material in front of you.
A COA does not describe what a compound does. It describes what was measured, by which technique, on which batch, and on which date.
The 8 things to check on a peptide COA
1. Compound identity
The report should name the compound tested, unambiguously, and that name should match the material it accompanies.
2. Batch or lot identifier
Without a batch or lot number, the report cannot be linked to a specific production run. An unlinked COA describes an unknown quantity of material.
3. Test date
Analytical results describe a sample at the time it was tested. A date anchors the result in time.
4. Laboratory / analytical source
The report should identify who performed the analysis. An anonymous report cannot be evaluated, questioned, or repeated.
5. Test method
Each stated result should be attributable to a named method — for example HPLC purity, chromatographic identity comparison, or quantitative assay. A number without a method has no defined scope.
6. Identity result
Look for evidence that the material corresponds to the expected molecular species, not merely that a peak was observed.
7. Purity / impurity result
Purity figures are method-specific. The report should make clear what was measured and, where available, what the impurity profile looked like.
8. Consistency between product, batch, and report details
Compound name, batch identifier, and the details printed on the physical material should agree with each other. Mismatches are a documentation failure regardless of how good the numbers look.
Identity vs. purity
These answer different analytical questions.
- Identity asks whether the material is the molecule it is labelled as. In the current GLUUM. testing program, it is assessed by chromatographic comparison against a reference standard.
- Purity asks what proportion of the detected material corresponds to the principal component under a given analytical method.
A sample can return a high purity value while identity remains unconfirmed, because purity describes the distribution of what was detected — not what that principal component actually is. Conversely, confirmed identity says nothing by itself about the level of related impurities.
What does HPLC tell you?
High-performance liquid chromatography separates the components of a sample as they pass through a column, producing a chromatogram in which distinct components appear as peaks. Analysts read:
- the principal peak, corresponding to the main component
- secondary peaks, indicating related substances or impurities
- the relative area of those peaks, which underpins reported purity percentages
Chromatography is well suited to describing how much of what was detected corresponds to the main component, and to revealing impurity patterns. Retention time can be suggestive of identity when compared against a reference standard under identical conditions, but retention time alone is not universally sufficient to establish identity — different substances can elute at similar times.
What does chromatographic identity testing tell you?
Chromatographic comparison assesses whether the sample's retention behaviour matches an appropriate reference standard under the stated conditions. In the current GLUUM. testing program, this comparison supports the identity result reported for the applicable lot.
Identity, purity, and quantitative content remain separate findings. Each result should be read alongside the method and lot stated on the certificate.
Why batch-specific testing matters
Analytical documentation is only as useful as the chain that connects it to physical material:
compound → batch / lot → analytical report → test date → result
Break any link in that chain and the report stops describing the material in question. Different production runs of the same compound are different material, and the results of one do not transfer to another. This is why a batch identifier and a test date are structural requirements of a credible COA, not optional details.
Does "99% purity" mean the material is 99% perfect?
No. A purity figure is scoped to the method that produced it. A chromatographic purity of 99% is a statement about peak area distribution under specific analytical conditions for a specific sample.
It does not, by itself, establish:
- identity — what the principal component actually is
- exact content — how much peptide is present by mass in the container
- sterility
- endotoxin levels
- microbial quality
- stability — how the material behaves over time or under different storage conditions
Each of those is a separate analytical question requiring its own method. A single percentage answers one of them.
Common COA red flags
- No batch link. The report cannot be tied to specific material.
- No stated method. A result with no defined analytical scope.
- Purity presented as identity. A percentage used to imply the molecule has been confirmed.
- Missing laboratory or source. No accountable party behind the numbers.
- Mismatched details. Compound name, batch, or dates that disagree across the report and the material.
- Implausible precision without context. Figures reported to a degree of certainty the stated method cannot support.
- One report reused indefinitely. A single document presented as covering every batch, past and future.
How GLUUM approaches testing transparency
GLUUM publishes available batch documentation in the COA Library, and product-level documentation is surfaced alongside the relevant compound in the catalogue.
Those live pages are the current source of record. Documentation availability varies by compound and by batch, and we do not claim that every current product has a published COA — check the live page for the compound you are evaluating.
Frequently asked questions
What is a peptide COA? A batch-linked analytical report documenting which tests were run on a specific lot of material, by what method, on what date, and with what results.
Is a COA the same as third-party testing? No. A COA is the report format. Third-party testing describes who performed the analysis — an independent laboratory rather than the producer. A COA may be produced either way, so the report should state its source.
What does 99% peptide purity mean? It usually means that, under a stated chromatographic method, roughly 99% of the detected peak area corresponded to the principal component. It is a method-scoped measurement, not a global quality score.
Does higher chromatographic purity always mean higher overall quality? No. Purity is one attribute among several. Identity, content, stability, and microbiological attributes are measured separately and are not implied by a purity figure.
Why does the batch number matter? It is what connects the report to physical material. Without it, the results describe an unidentified production run.
Is HPLC enough to confirm peptide identity? Not from a purity percentage alone. The current GLUUM. program reports identity through chromatographic comparison against a reference standard, separately from HPLC purity.
What should a researcher ask if a supplier does not publish a COA? Ask which batch the material comes from, whether a batch-specific analytical report exists, which methods were used, who performed the analysis, and when. Absence of documentation is itself information.
References and further reading
- FDA Q7A Good Manufacturing Practice Guidance for Active Pharmaceutical Ingredients
- FDA Analytical Procedures and Methods Validation for Drugs and Biologics
- FDA/ICH Q2(R2) Validation of Analytical Procedures
- FDA/ICH Q6A Specifications: Test Procedures and Acceptance Criteria for New Drug Substances and New Drug Products: Chemical Substances
- Reference Standards to Support Quality of Synthetic Peptide Therapeutics (PMID 36949371)
Research use notice. This article is educational material about analytical documentation only. It is not medical advice, does not describe biological effects, and contains no human-use instructions. All GLUUM compounds are for laboratory research use only. Not for human consumption.
Preserve the evidence chain after acceptance
A research record should make it possible to reconstruct which material was accepted, which report informed the decision, and which experimental samples came from it. Supplier pages can change, instrument data can be reprocessed and internal sample identifiers can differ from supplier lot numbers.
FDA’s data-integrity guidance concerns drug CGMP. It explains record concepts here, not identical legal obligations for all research laboratories. It defines metadata as contextual information needed to understand data and emphasizes preserving data–metadata relationships. FDA data-integrity guidance
Keep the decision-time specification and report with supplier, material designation, lot, receipt date and discrepancies. Retain an original and corrected report together with the correction explanation instead of silently replacing the original.
Expected specifications and measured results are different fields. ICH Q7 likewise distinguishes acceptance limits and numerical results on certificates. ICH Q7, §11.43
Map supplier lot to receipt identifier, study sample identifiers and analytical files. Names need not match; their relationships must remain explicit. Record relevant departures when they occur rather than reconstructing them from memory after an unexpected finding.
For laboratory-generated measurements, retain method version, sample identity, units, calculation basis and relevant acquisition context. A screenshot may not retain everything needed to reconstruct electronic analysis. Distinguish a certificate, trace, export and raw dataset from information not obtained; this does not require every purchaser to possess a laboratory’s proprietary instrument environment.
FDA specifically discusses HPLC integration parameters and reprocessing history in audit trails. Preserve original information, changed parameters and the reason for changes so the reported result can be reconstructed. FDA data-integrity guidance
Organization improves traceability, not proof of GMP, batch representativeness or a correct biological conclusion. Its practical value is identifying material, recovering the decision-time evidence and separating observations from assumptions.