A peptide Certificate of Analysis (COA) is a document that reports the results of analytical testing on a specific lot of material, typically HPLC purity, mass spectrometry identity, and sometimes net peptide content, water content, and endotoxin. It is lot-specific by definition. A COA that does not name a lot or batch number is a product specification, not a certificate of analysis. The guide to reading a peptide COA explains each field. This FAQ covers the separate question of whether the document can be trusted.
Who issues a peptide COA?
A COA is issued either by the manufacturer's own quality control lab, by a contract lab the manufacturer hired, or by an independent third-party lab commissioned by the vendor or the researcher. The issuer should be named on the document. A vendor-issued COA is release testing from the point of manufacture. A third-party COA is testing on the finished product. Both are legitimate. The verification steps differ because the incentive structure differs: a third-party lab has no stake in the result, so its identity and report ID are the things to confirm, while a manufacturer COA needs its lot number matched against what actually shipped.
How do I verify a peptide COA is genuine?
Verification is a five-step check: match the lot number on the COA to the lot number on the vial label; confirm the issuing lab exists and can be contacted independently of the vendor; ask the lab to confirm the report ID and date; check that the document includes the analytical method (column, gradient, wavelength) and the raw chromatogram or mass spectrum rather than a summary number; and check that the analysis date is plausible relative to the ship date. A COA that passes all five is a real document describing a real test on the lot in hand. A COA that fails the lot match is, at best, a different batch's data.
What does "99% purity" on a COA actually measure?
A 99% purity figure on a COA is the target peak's share of the total integrated peak area in a reverse-phase HPLC run, measured at the stated detection wavelength. It is a relative measurement of peptide-like material, not the absolute amount of peptide in the vial. It counts only what the method separates and the detector sees. Impurities that co-elute with the main peak are integrated as target. Non-absorbing components such as water and counter-ions do not register at all. The number is real, but it answers "of the peptide species present, what fraction is the right one," not "how much peptide is in this vial."
Why does net peptide content differ from purity?
Net peptide content is the fraction of the vial's total mass that is peptide, while purity is the fraction of detected peptide species that is the target. A lyophilized peptide carries bound water and counter-ions, usually trifluoroacetate or acetate from purification, which can account for 10% to 30% of the mass. A vial at 99% HPLC purity may therefore contain 70% to 90% peptide by weight. Net peptide content requires amino acid analysis or a comparable quantitative method, and most vendor COAs do not include it. The net peptide content explainer covers the calculation.
What are the red flags of a fabricated COA?
The common signs of a fabricated or recycled COA are: no lot number, or a lot number that does not match the vial; a purity figure with no chromatogram; no analytical method listed; a round-number purity like exactly 99.0% repeated across every product the vendor sells; a lab name that returns no independent web presence or phone number; an analysis date that precedes the product's first listing by years or follows the ship date; a mass spectrum with no observed versus theoretical mass comparison; and a template layout that appears identically on other vendors' sites with only the product name swapped. Any two of these together warrant a third-party test before the material is used.
Can a COA be real but for a different batch?
Yes, and this is the most common failure mode. A vendor may test one lot thoroughly, publish that COA, and continue to display it as new lots arrive. The document is genuine; it just does not describe the material being shipped. The lot match is the check that catches it. Vendors that publish per-lot COAs, dated and numbered, and rotate them as inventory changes are addressing this directly. Vendors displaying a single undated "representative" COA are not.
What is the difference between HPLC purity and mass spec identity?
HPLC purity reports how clean a sample is; mass spectrometry identity reports what it is. A sample can be 99% pure by HPLC and be the wrong peptide, because HPLC separates by hydrophobicity and does not read mass or sequence. Mass spectrometry measures the molecular weight of the main peak and compares it to the theoretical value from the sequence. A COA that reports both, with the observed mass within instrument tolerance of the theoretical, has answered both halves. A COA that reports only HPLC purity has answered one.
How do I verify the issuing lab?
Verify the lab by finding its contact details from a source other than the COA or the vendor's site, then contacting it with the report ID. Accredited labs appear in the public registers of their accreditation body, such as A2LA or ANAB in the United States and UKAS in the United Kingdom, and those registers list the lab's accredited scope. A lab that exists, answers, and confirms the report ID has verified the document. A lab whose only footprint is the logo on the COA has not.
Do UK and EU researchers verify a COA differently?
The verification logic is the same; the reference points differ. UK researchers can check a lab's ISO/IEC 17025 accreditation through the UKAS register, and EU researchers through their national accreditation body listed under the European co-operation for Accreditation. Imported material from US or Asian suppliers will usually carry a manufacturer COA from the country of origin; the lot match and the method disclosure checks apply unchanged. Researchers in either region commissioning their own third-party test should confirm the lab's scope covers peptide HPLC and mass spectrometry specifically, since accreditation is scope-limited.
What should a COA include for a compound used in cell-based research?
For material going into cell culture work, the COA should include endotoxin (reported from a LAL assay in endotoxin units per milligram) in addition to purity and identity, and ideally water content by Karl Fischer titration. Endotoxin contamination confounds inflammatory and redox pathway readouts, which matters for the longevity and cellular aging models Ever Vital's catalog is oriented toward. A COA lacking an endotoxin result is not disqualifying for every application, but it leaves that variable uncontrolled.
How often should a peptide lot be re-tested?
A lot should be re-tested when it has been stored past the manufacturer's stated stability window, when storage conditions were interrupted, when a result depends critically on concentration, or when the original COA fails any verification step above. Lyophilized peptides stored at minus 20 degrees Celsius and protected from light are generally stable for the period stated on the COA, but a COA describes the lot at the time of analysis, not indefinitely.
Can a vendor's own testing be trusted at all?
A vendor's own testing can be trusted to the extent it is disclosed and matches. A manufacturer COA with lot number, method, chromatogram, and mass spectrum, that matches the vial and that a third-party test on the same lot corroborates, is strong evidence. The verifying peptide testing claims article covers how to weigh vendor claims against independent results. The principle is that documentation is verified by matching, not by trusting the letterhead.
What is the minimum acceptable COA for research use?
The minimum acceptable COA names the compound and lot, states the HPLC method and purity with the chromatogram attached, reports observed and theoretical mass from mass spectrometry, is dated, and identifies the issuing lab. Anything less is a specification sheet. Ever Vital publishes per-batch HPLC and mass spectrometry documentation for its catalog, and researchers are encouraged to commission independent testing on any lot where the application requires it.
All compounds referenced in this article are supplied for research purposes only and are not for human use. Nothing here describes or endorses any use of these materials outside laboratory research. These products are not intended to diagnose, treat, cure, or prevent any disease.
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