The seven sections every COA should have
1. Batch identification
Peptide name, sequence, batch/lot number, manufacture date, and vial label match. If the lot on the COA does not match the vial in your hand, stop.
2. Identity (mass spec)
Observed mass, theoretical mass, mass error, and the raw MS trace. Confirms the molecule is what the label claims.
3. Purity (HPLC)
Percentage by area under the main peak, the HPLC method used, and the attached chromatogram. Without the chromatogram the number is unverifiable.
4. Contaminants
Endotoxin (LAL, USP <85>), heavy metals (USP <232>/<233>), residual solvents (USP <467>). Required for anything intended for injection.
5. Physical characteristics
Appearance (white lyophilized cake, off-white powder, etc.), residual moisture, counterion (TFA or acetate), and net peptide content.
6. Storage & handling
Recommended storage temperature, shelf life, reconstitution guidance. Should match your storage capabilities.
7. Lab attestation
Name and accreditation of the testing laboratory, method references, analyst signature, and report date. Third-party COAs should name a lab you can look up independently.
Reading the HPLC chromatogram
The chromatogram is the piece most researchers underweight. Look at three things:
- Main peak symmetry. A tailing or fronting peak often hides co-eluting impurities that inflate the reported purity.
- Impurity clustering. Peaks that elute within 1–2 minutes of the main peak are the hardest to separate. Their presence in size matters more than their count.
- Baseline noise. A noisy baseline in the region of the impurities suggests the integration is optimistic.
If the summary says 99% and the chromatogram shows visible secondary peaks with obvious area, the integration or the method conditions do not match. Ask for the raw data file.
Mass spectrometry: what the numbers mean
| Mass observation | Likely cause |
|---|---|
| Matches theoretical within 0.01 Da | Correct sequence, high-res instrument |
| Matches within 0.5 Da (MALDI-TOF) | Correct sequence, standard instrument |
| +1 Da from theoretical | Deamidation of Asn or Gln |
| +16 Da from theoretical | Oxidation, usually Met, Cys, or Trp |
| -18 Da from theoretical | Dehydration or cyclization |
| Off by an amino acid residue mass | Synthesis truncation, wrong sequence |
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- validated analytical methods, independent of any supplier
- 5–7 business days for eligible routine testing
- Traceable COA with chromatograms and method parameters
Contaminants: acceptable limits
- Endotoxin (LAL): USP injectable limit is 5 EU/kg body weight per hour parenteral. Batch-level: typically under 0.5 EU/mg for research injectables.
- Heavy metals: USP <232> sets PDE limits for As, Cd, Hg, Pb and other elements. ICP-MS is the reference method.
- Residual solvents: USP <467> classifies solvents. Class 2 solvents (DMF, acetonitrile) have PDE limits typically under 4,110 ppm.
- Microbial: USP <61>/<62> bioburden and specified organisms. Required for pharmaceutical use.
The nine red flags
- No chromatogram attached to the purity claim
- Batch number missing or does not match the vial label
- Purity reported without the HPLC method
- Mass spec section absent or shows only theoretical mass
- Testing lab not named, or lab has no accreditation you can verify
- Report date more than 12 months old for a peptide sold today
- Endotoxin, heavy metals, or solvents missing for an injectable-grade product
- Chromatogram shows secondary peaks that do not reconcile with the reported purity
- Manufacturer refuses to release the raw data on request
Any single flag is grounds for an independent retest. Two or more and the COA should not be trusted.
When and why to request a third-party COA
A vendor COA proves the batch passed the vendor's tests. A third-party COA proves the batch passes anyone's tests. If the batch will be injected, dispensed to patients, used in a publication, or resold, the third-party test is the safety layer that catches the failure modes a vendor is not incentivized to find.
See also: in-house vs third-party testing, and what third-party purity testing costs.
Reading a Peptide COA: FAQ
A COA is a signed document from a testing laboratory that reports the analytical results of a specific batch of material. For peptides it should list identity (mass spec), purity (HPLC), and typically contaminants (endotoxin, heavy metals, residual solvents). It should reference the batch number, test date, method, and the accreditation status of the issuing lab.
For research peptides, 95%+ by HPLC is the industry benchmark and 98%+ is common for high-grade material. Below 95% suggests either a difficult synthesis or insufficient purification. For compounding pharmacy use, standards are higher and 99%+ is typical. Always compare against the individual peptide's monograph if one exists.
A number without a chromatogram cannot be verified. The chromatogram shows the actual detector trace: whether the main peak is symmetric, whether impurities cluster near the main peak (harder to separate), and whether the reported purity percentage matches the visible area integration. A COA without the chromatogram attached is a marketing document, not analytical evidence.
The observed [M+H]+ or [M+2H]2+ ion should match the theoretical monoisotopic mass within 0.5 Da for MALDI-TOF or 0.01 Da for high-resolution instruments. A mass off by 1 Da usually indicates deamidation. A mass off by 16 Da usually indicates oxidation. A mass off by the weight of a full amino acid indicates a synthesis truncation.
Both have value but they answer different questions. A manufacturer COA proves the batch was tested during production. A third-party COA proves the batch matches what the manufacturer claimed, using an independent lab with no financial stake in the result. Compounding pharmacies and serious research labs typically require both.
USP <85> for endotoxin, USP <232>/<233> for heavy metals, and USP <467> for residual solvents are the relevant compendial methods. The COA should reference the method and the applicable standard.
No chromatogram attached. Purity reported without the method used. Batch number missing or not matching the vial label. Test date more than 12 months old. Lab name absent or the lab has no accreditation. Impurity peaks visible in the chromatogram that are not accounted for in the summary. Any of these individually is a reason to request a third-party retest.
Yes. Independent verification is the reason third-party labs exist. ACS runs HPLC purity, mass identity, and contaminant panels on customer-submitted samples with a 5–7 business day turnaround. If the results diverge from the original COA, we provide the full chromatogram and methods so you can raise it with the manufacturer.