How to read a certificate of analysis
Read a certificate of analysis as a set of separate answers: who tested the material, which lot, whether it is the right molecule, how clean the main component is, and what else was measured.
Each section comes from a different method and answers a different question. None of them can stand in for another, and none of them means anything unless the lot number matches the vial.
A certificate of analysis, or COA, is the document that links a lot of research material to its test results. Knowing how to read a certificate of analysis is mostly a matter of knowing which question each line answers, and which questions the page leaves open. This guide takes a typical peptide certificate from the top down. For the purity line in detail, see our explainer on what an RP-HPLC purity number actually measures.
Scope: this is a guide to analytical documents for laboratory readers. The research use policy sets out how materials on this site are supplied.
Who produced the certificate
Start at the top of the page, before any result. A certificate is only as good as the laboratory behind it and the link between the page and the lot.
Lot number
The identifier for one production batch. Every result on the page belongs to this lot and to no other.
Specification
The acceptance limit set before testing. It is the target, not the finding.
Result
The value actually measured on the sample from that lot, on the stated test date.
The laboratory should be named, with an address or other means of identifying it. The international standard for laboratory competence, ISO/IEC 17025:2017, sets general requirements for the competence, impartiality and consistent operation of testing and calibration laboratories. Accreditation to it is granted for specific work, not for the laboratory as a whole. The accreditation body A2LA describes a scope of accreditation as the list of specific tests for which a laboratory has been found competent, and states that capabilities not listed on the scope are not covered by the accreditation. An accredited laboratory can still run a test that sits outside its scope.
The identity section: is it the right molecule
Identity asks whether the material is the peptide named on the label. For peptides it is usually answered by mass spectrometry, often coupled to liquid chromatography as LC-MS, with the measured mass reported next to the mass expected for the stated sequence.
Two things follow that are widely misunderstood. First, a mass match confirms one property, the molecular weight. It does not prove the sequence on its own, because different chains, or the same residues in a different order, can share a mass. Second, identity and purity are separate claims. A certificate can show a clean chromatogram of the wrong molecule.
Regulators treat identity as something to establish with more than one line of evidence. In guidance published in May 2021 for generic versions of five synthetic peptide drugs, FDA encourages applicants to use orthogonal analytical methods to characterize properties including the primary sequence. That guidance covers drug applications; it is cited here for the principle, not as a standard research certificates are held to. Our profile of BPC-157 shows how a sequence and its expected mass are stated in practice.
The purity section: how clean is the main component
Purity is usually reported from reversed-phase HPLC. The harmonized USP general chapter on chromatography describes the normalization procedure behind most purity figures: the area of one peak as a percentage of the total area of all peaks, excluding peaks from solvents, reagents, the mobile phase or the sample matrix.
A purity figure says what share of the detected peak area belongs to the main peak. It does not say how much of the powder in the vial is peptide.
- Method and conditions. The column, gradient and detection wavelength should be named. Change them and the separation changes.
- The chromatogram. A trace with integrated peaks lets a reader see what the number was calculated from.
- Separation power. The ICH Q2(R2) validation guidance, issued by FDA in March 2024, states that for critical separations specificity can be shown by the resolution of the two components that elute closest to each other. Impurities that merge with the main peak are counted as target.
- What the other peaks are. A review of related impurities in peptide medicines by D’Hondt and colleagues groups them into synthesis related impurities, such as deletions, insertions and diastereomers, and degradation products. Area percent reports how much signal is not the main peak, not which of these it is.
Other results a certificate may report
Some certificates stop at identity and purity. Others add further tests. Each is a separate method with its own units and its own limit, and each answers a narrower question than it may appear to.
- Salt form or counterion. Synthetic peptides are commonly supplied as salts. The D’Hondt review notes that counterions such as trifluoroacetate, left from synthesis or purification, can remain in the final material. They add weight without adding a peptide peak.
- Water content. Lyophilized material can hold residual moisture, measured by its own method. It is not visible in a UV chromatogram.
- Net peptide content. Where it is reported, it expresses how much of the weighed powder is the peptide itself, after water, counterions and other non peptide material are accounted for.
- Bacterial endotoxins. FDA’s questions and answers guidance on pyrogen and endotoxins testing, edition 2 of March 2026, refers to USP chapter <85>, the bacterial endotoxins test, and describes gel clot, photometric and kinetic methods based on Limulus Amoebocyte Lysate (LAL). An endotoxin result answers a contamination question. It says nothing about identity or purity.
What a certificate cannot tell you
A well built certificate is still a record of one sample, on one date, under the tests that were run. These are the questions outside it.
- Tests that were not run. A blank section is not a pass. If a result is not on the page, it was not reported.
- Another lot. Results belong to the lot tested. They do not transfer to material made on another day, even under the same product name.
- What happened after the test date. Storage and handling after testing can change the material. Our article on cold chain and storage temperature covers why.
- Whether this page belongs to this vial. Only the lot number can answer that, and only if it matches exactly.
Reading a certificate line by line
With the sections in place, a certificate can be checked in a few minutes. Work through it in this order and stop at the first item that does not hold.
- Lot number on the certificate matches the vial label exactly
- Testing laboratory named and identifiable
- Test date stated
- Compound name and sequence stated
- Identity reported as measured mass against expected mass
- Purity method, column and detection wavelength named
- Chromatogram attached with integrated peaks visible
- Specification and result reported separately
- Salt form or counterion stated
Iron Rack Labs publishes lot matched certificates in the certificate of analysis library, searchable by compound or lot number, and the quality and testing page explains which tests are run on each lot. Pick any lot record there and read it against this list.
- Each section of a certificate answers a different question
- Accreditation covers only the tests listed on the laboratory’s scope
- A mass match is evidence of identity but does not prove the sequence alone
- Purity is a peak area ratio under one method, not a weight
- Every result belongs to one lot and one test date
Frequently asked questions
A certificate of analysis is a document that reports the test results for one specific lot of material. It names the laboratory, the lot number and the test date, and lists results such as identity and purity against their specifications. Its value depends on the lot number matching the vial and on each result naming the method behind it.
Identity asks whether the material is the named molecule, usually by comparing a measured mass with the expected mass. Purity asks what share of the detected chromatographic signal belongs to the main peak. They come from different methods and answer different questions, so a high purity figure does not confirm identity on its own.
No. Accreditation to ISO/IEC 17025 is granted for specific tests listed on the laboratory’s scope of accreditation. Accreditation bodies state that capabilities not on the scope are not covered. A certificate from an accredited laboratory is strongest when the method used for each result appears on that scope.
Because every result on a certificate belongs to the lot that was sampled and tested. Material from a different lot, even with the same product name, may differ in purity, impurities or content. The lot number is the only link between the page and the vial, so it should match exactly before any result is relied on.
It remains an accurate record of the lot as tested on that date. It does not describe changes that happen afterward. Peptides can degrade with heat and moisture, so how the material has been stored since testing matters. The certificate should be read together with the storage history of the vial.
- ISO/IEC 17025:2017, General requirements for the competence of testing and calibration laboratories. ISO, 2017. View source
- Frequently Asked Questions, scope of accreditation. American Association for Laboratory Accreditation (A2LA). View source
- ANDAs for Certain Highly Purified Synthetic Peptide Drug Products That Refer to Listed Drugs of rDNA Origin, Guidance for Industry. U.S. Food and Drug Administration, May 2021. View source
- USP General Chapter <621>, Chromatography. Harmonized standard, official December 1, 2022. United States Pharmacopeia, 2022. View source
- Q2(R2) Validation of Analytical Procedures, Guidance for Industry. U.S. Food and Drug Administration, March 2024. View source
- D’Hondt M, Bracke N, Taevernier L, Gevaert B, Verbeke F, Wynendaele E, De Spiegeleer B, 2014. Related impurities in peptide medicines. Journal of Pharmaceutical and Biomedical Analysis, 101, 2 to 30. DOI
- Pyrogen and Endotoxins Testing: Questions and Answers, Guidance for Industry, Edition 2. U.S. Food and Drug Administration, March 2026. View source
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