A peptide certificate of analysis can contain an impressive purity figure and still leave important questions unanswered. Does the report cover the batch you will receive? What did the laboratory actually measure? Was the finished formulation tested, or only the starting material?
Read a peptide COA in this order: match the product and batch, identify the tested sample, review the methods and results, then check what was not assessed. A certificate supports a decision only within the scope of its evidence.
This guide explains the main fields, common analytical terms and a worked example for laboratory buyers. It concerns research materials; a COA is not evidence that a product is authorised or suitable for human treatment.
What is a peptide COA?
A certificate of analysis is a document reporting analytical information for an identified material or batch. It may include specifications, test methods, results and a statement of whether the material meets the listed requirements.
As a documentation benchmark, ICH Q7 identifies batch details, tests, acceptance limits and numerical results among the information expected on certificates for pharmaceutical active ingredients.[1] Its pharmaceutical scope should not be mistaken for a universal legal requirement covering every research peptide. Here is some guidance to UK peptide legality.
For a laboratory buyer, the objective is practical: connect the material being purchased to meaningful, interpretable results.
1. Match the certificate to the material
Before reading the percentages, compare the document with the product specification and container label.
| Field | What to check |
|---|---|
| Product identity | Does the name and any stated sequence, modification or formulation match the item ordered? |
| Batch or lot | Can the supplied container be connected to this batch? |
| Sample reference | Is there a documented link between the laboratory’s sample code and the supplier’s lot? |
| Report number and version | Can you identify the complete report and any subsequent revision? |
| Issuer | Who issued the certificate, and who performed the analysis? |
Laboratories and UK peptide suppliers may use different identifiers. Different codes are not automatically suspicious, but an unexplained mismatch needs resolving.
Ask for the complete report if you have only a cropped screenshot. A missing page may contain the methods, qualifications or sample description needed to interpret the result.
2. Establish what was sampled
A genuine report can still describe material at a different stage from the product you intend to buy.
Ask whether the sample was a bulk peptide powder, a formulated mixture or material taken from the final packaged product. For a pre-mixed solution, an upstream powder certificate does not establish the solution’s concentration or its condition after formulation.
Also ask who selected and submitted the sample. Testing by an independent laboratory does not necessarily mean the laboratory independently collected a representative sample from the supplier’s stock.
The purchasing inference is limited: a report describes the tested sample, and its relevance to your order depends on the documented connection to the supplied material. Keep that connection in your procurement record.
3. Separate the specification from the result
Certificates often place an acceptance criterion beside a measured value. Read both columns.
For example, an illustrative purity requirement of “at least 98.0%” and a reported result of “99.2%” are not two measurements. The first is the criterion; the second is the test outcome. Those fictional values are not recommended specifications for any particular experiment.
A statement such as “conforms” needs context. What requirement was applied, and which test supports that conclusion? For a numerical characteristic, request the numerical result when your decision depends on it. Some qualitative tests legitimately report an observation or identification conclusion rather than a percentage.
Do not treat a supplier’s overall “pass” as confirmation that the product meets every requirement of your laboratory. Compare the listed specifications with your own protocol.
4. Interpret HPLC purity correctly
High-performance liquid chromatography, or HPLC, separates sample components under defined analytical conditions. When purity is reported as an area percentage, it generally describes the proportion of the included chromatographic signal assigned to the target peak.
Sigma-Aldrich’s technical explanation distinguishes HPLC peptide purity from peptide content. Its HPLC measurement does not account for water and salts in the sample.[2] A chromatographic percentage therefore should not be read as the percentage of the container’s entire mass that consists of the intended peptide.
Check whether the report identifies the method and detector conditions. Where supporting chromatograms are available, ask for the peak assignment and integration information rather than trying to estimate purity from the height of the largest peak.
What can a clean chromatogram miss?
Interpretation depends on the method’s ability to distinguish relevant components. ICH Q2(R2) discusses assessing interference and using complementary procedures where one method cannot provide sufficient discrimination.[3]
The practical implication is that a dominant peak is not universal proof that every possible impurity was measured. If a particular impurity matters to the experiment, ask whether the method can detect or resolve it.
5. Read the identity evidence separately
Look for an identity test alongside the purity result. Mass spectrometry, abbreviated to MS, is often part of peptide characterisation, but the label “MS” does not tell you how extensive the assessment was.
Check what is reported: molecular-mass consistency, comparison with a reference, peptide mapping or sequence information from tandem mass spectrometry. NIST discusses these as distinct approaches contributing qualitative information about peptides and proteins.[4]
A statement that the observed mass agrees with the expected mass should be interpreted at that level. Do not expand it into a claim that every aspect of the molecule’s structure has been verified.
Where identity is critical, ask your laboratory’s analytical specialist whether the supplied evidence is sufficiently discriminating for the compound and likely alternatives.
6. Find out whether quantity was measured
Look for a separately defined content, assay or concentration result. Ask what was measured, how it was measured and which units apply.
For example, a result expressed as milligrams per millilitre answers a different question from a chromatographic area percentage. A fill quantity printed in the product description is not automatically an analytical measurement.
BIPM, the international metrology organisation, describes peptide mass-fraction assessment using approaches including mass balance and peptide-impurity-corrected amino acid analysis.[5] This illustrates why assigning the amount of a target peptide requires attention to other material in the sample and to the measurement approach.
If quantity is absent from the COA, record it as unreported. Do not infer it from a purity result or calculate target-peptide mass by subtracting only the water percentage: other constituents may remain unaccounted for.
7. Understand “not detected”, limits and unperformed tests
Three statements that can look reassuring mean different things:
| Report wording | How to interpret it |
|---|---|
| Not detected | Ask which analyte was sought and what detection or reporting limit applies. It does not establish absolute absence. |
| Below the quantitation limit | The method does not support a reliable numerical quantity below the stated threshold; the substance may still have been detected. |
| Not tested | No result was generated for that characteristic in the stated testing scope. |
ICH Q2(R2) distinguishes detecting an analyte from quantifying it with suitable performance.[3] Ask the issuing laboratory to explain its abbreviations and reporting conventions, including “ND”, “DL” or “LOD”, and “QL” or “LOQ”.
Check units before comparing results. Values reported per millilitre, per milligram and per container cannot be compared directly without the information needed for conversion.
Purity is not a microbiological result
HPLC purity, sterility and bacterial endotoxin testing address different characteristics. A result for one does not establish the others. FDA guidance treats bacterial endotoxin testing as a distinct assessment with method-specific considerations.[6]
If microbiological quality matters to your experiment, request the relevant tests, methods, units and acceptance criteria. An absent result is a gap to assess against your protocol, not automatic proof of contamination.
Worked example: reading a fictional peptide COA
This simplified example is entirely fictional. It is not a Coridion Sciences report, a complete certificate template or a recommended testing specification.
Suppose a report contains the following entries:
| Field | Fictional entry |
|---|---|
| Product | Research Peptide X, bulk lyophilised material |
| Batch | EXAMPLE-01 |
| Sample | Supplier-submitted sample from the named bulk lot |
| Analysis date | 12 September 2026 |
| Report date | 14 September 2026 |
| HPLC purity | 99.2% area; stated criterion: at least 98.0% |
| Identity | Observed molecular mass consistent with the stated target |
| Target-peptide content | Not reported |
| Sterility | Not tested |
| Bacterial endotoxins | Not tested |
What the report supports
Within this example, the reported HPLC result meets the listed chromatographic acceptance criterion. The identity statement supports consistency with the target’s expected molecular mass. The document also identifies the bulk lot and describes how the sample was submitted.
What remains unanswered
The entries do not establish the amount of target peptide in an individual container, microbiological quality or the concentration of a later formulated solution. They also do not show independent sampling by the testing laboratory.
If your order concerns a solution made from this bulk lot, request the link to the formulation batch and whatever finished-product evidence your experiment requires. If it concerns dry material from the same lot, establish how the final containers are linked to the report.
The appropriate conclusion is specific: the reported sample met the listed HPLC criterion; additional purchasing requirements still need their own evidence.
8. Check dates and authenticate the report
An analysis date records when testing occurred; a report date records when the document was issued. Neither should be assumed to establish a shelf life. Ask separately about any expiry or retest date and the supporting storage conditions.[1]
An older report is not automatically invalid, and a recent one is not automatically sufficient. Assess the lot, storage history and supplier’s explanation together.
To verify a report, identify the issuing laboratory through its official website. Where available, use its verification service or contact it with the report reference. A QR code is a route to information, not proof of authenticity by itself.
If laboratory accreditation is claimed, check the relevant scope. UKAS explains that accreditation covers specified activities; the organisation’s published schedule identifies what is included.[7] A logo does not establish that every test offered by the laboratory is covered.
Authentication and adequacy are separate checks. A verified report can still omit a test your experiment needs.
Here is a full guide on what to check before buying peptides online.
Questions to send when a COA is incomplete
- Does this report cover the batch and formulation that will be supplied?
- How is the laboratory sample reference linked to the supplier’s lot?
- What do the purity and quantity results each measure?
- What identity conclusion is supported by the actual method?
- Which relevant characteristics were not tested or not reported?
- Can the report be authenticated, and can supporting analytical data be provided?
Keep the answers with the COA and your order records. Where a gap affects suitability, obtain clarification or additional evidence before releasing the material for use.
When reviewing research peptides from Coridion Sciences, ask which batch documents are available for the exact product and format you are considering. Apply the same review to the document received, rather than relying on a general description of testing elsewhere on the website.
Sources
- US Food and Drug Administration / ICH. Q7: Good Manufacturing Practice Guidance for Active Pharmaceutical Ingredients, sections 11.4–11.6. Used as a pharmaceutical documentation benchmark, not as a statement of universal requirements for UK research reagents.
- Sigma-Aldrich. Peptide Sample Amount Determination. Technical explanation distinguishing peptide purity from peptide content.
- US Food and Drug Administration / ICH. Q2(R2): Validation of Analytical Procedures, specificity/selectivity, lower range limits and glossary. Used for analytical principles and terminology, not to imply that a particular supplier’s methods have been validated to this standard.
- Bunk D, Lowenthal M. Isotope Dilution Liquid Chromatography–Tandem Mass Spectrometry for Quantitative Amino Acid Analysis. NIST, 2019. Discusses molecular-mass measurement, peptide mapping, sequencing and quantitative amino acid analysis.
- Bureau International des Poids et Mesures. Peptides/Proteins. Primary metrology guidance describing approaches to peptide purity value assignment and impurity characterisation.
- US Food and Drug Administration. Pyrogen and Endotoxins Testing: Questions and Answers, Edition 2, 2026. Cited for the distinct nature and method considerations of endotoxin testing; pharmaceutical acceptance limits should not be applied indiscriminately to laboratory research materials.
- UKAS. Accreditation vs Certification: What’s the Difference?. Explains activity-specific accreditation and published schedules.