The seven sections every COA should have
1. Batch identification
2. Identity (mass spec)
3. Purity (HPLC)
4. Contaminants
5. Physical characteristics
6. Storage & handling
7. Lab attestation
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 |
Ready to test your peptides?
Send your peptide name, sample count, and the tests you need. We return a fixed-price quote, usually within one business day.
- validated analytical methods, independent of any supplier
- 9-11 business day standard turnaround
- 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.