← Knowledge · Updated 6 November 2026 · 5 min read
A certificate of analysis (CoA) documents the test results for one specific lot. It applies to that lot only.
Check the match first
The lot number on the CoA must match the vial and the delivery note. Also check the name, the sequence and the test date.
The key values
- Identity: usually by mass spectrometry. The measured mass is compared to the calculated mass.
- Purity: usually by RP-HPLC, stated as area percent. The chromatogram should be attached.
- Peptide content: the share of peptide in the weighed material. This is not the same as purity.
- Water and counterions: these explain the gap between weighed mass and peptide content.
- Method and release: testing lab, method, date and the person who released it.
The structure of a typical CoA
Most certificates of analysis follow a similar layout. Knowing it helps you find the key figures faster.
- Header: name and address of the testing lab, client, report number and date of issue.
- Sample details: product name, sequence, lot number, declared amount and date the sample arrived.
- Test plan: which tests were run with which method, such as RP-HPLC, ESI-MS or Karl Fischer titration.
- Results: measured values, usually next to the specification, meaning the required limit.
- Attachments: chromatogram with peak table, and mass spectrum.
- Release: name and signature of the responsible person, often with the note “complies with specification”.
Telling specification from result
Many certificates give two values per test. The specification is the requirement, such as “purity ≥ 98.0%”. The result is the measured value, such as “98.6%”. If only “complies” appears without a figure, you only know the limit was met, not by how much. A certificate with measured values is therefore more informative.
An example: how to read the values
The values below are a made-up example. They show how the figures relate to each other.
| Figure | Example value | What it means |
|---|---|---|
| Calculated molecular mass | 1419.5 Da | Calculated from the sequence |
| Measured molecular mass (ESI-MS) | 1419.7 Da | Within the usual tolerance, so identity is supported |
| Purity (RP-HPLC, 214 nm) | 98.6% | The main peak is 98.6% of the peak area |
| Peptide content | 82% | 1 mg of weighed material holds about 0.82 mg of peptide |
| Counterion | Acetate | Part of the remaining mass is salt |
So in this example a vial with 5 mg of lyophilisate holds about 4.1 mg of peptide. How to allow for this in stock solutions is in Peptide content vs purity.
Checking the mass spectrum
With electrospray ionisation, peptides pick up several protons. The spectrum then shows not the mass itself, but several signals for the mass-to-charge ratio. For a peptide of 1419.5 Da, the doubly charged ion sits at about m/z 710.8, that is (1419.5 + 2 × 1.008) ÷ 2. The software converts these signals back to the neutral mass. The certificate should show this calculated mass next to the theoretical one.
With MALDI-TOF the singly charged ion usually appears, meaning the mass plus about 1 Da. Check whether the certificate states which ion was evaluated. A deviation of a few tenths of a dalton is normal on common instruments. Deviations of 16 Da or of an amino acid’s mass, on the other hand, point to oxidation or a deletion sequence.
Checking the chromatogram
- Wavelength: 214 to 220 nm is usual for peptides. At 280 nm you only see peptides with tryptophan or tyrosine.
- Peak table: it lists each integrated peak with retention time and area share. The total should be 100%.
- Main peak: it should be sharp and symmetrical. A shoulder on the peak can point to a closely related impurity.
- Baseline: a noisy or steeply rising baseline makes integration harder and hides small impurities.
What a CoA does not cover
A certificate only proves the tests listed on it. Sterility, endotoxins, heavy metals or residual solvents are not tested unless they are named. A CoA also says nothing about stability after opening or in solution. The safety data sheet and your own experience are the guide there.
Who issued the certificate
A certificate can come from the manufacturer or from an independent lab. Both can be acceptable, but an independent lab builds more trust. Accreditation to ISO/IEC 17025 shows the lab has been assessed for the methods named. You can check an accreditation with the national accreditation body, in Germany DAkkS.
How much does purity tell you?
An HPLC purity above 98% says the chromatogram shows few other peptides. It says nothing about water, salts or residual solvents. Only mass spectrometry shows whether the main peak is the right peptide. Why the two methods belong together is explained in HPLC and mass spectrometry.
Warning signs
Be careful with a missing lot number, purity figures with no method or chromatogram, and identical values across several lots.
Other signs are a CoA with no testing lab or date, a test date before the manufacturing date, and chromatograms that look the same for different peptides.
Filing certificates in the lab
Save each certificate with the lab notebook entry in which the lot was used. Name the file with product and lot number so it can be found quickly later. For queries, complaints or reviewing results that deviate, the certificate is the first point of reference.
Common questions about the CoA
Does one CoA cover every delivery of a product? No. It describes only the lot tested. A new lot needs its own certificate.
What is the difference between a CoA and an earlier analysis? An earlier analysis shows the result for an older sample. It says something about past quality, but nothing binding about the current lot. Our earlier lab results are public under Analyses.
How long is a certificate of analysis valid? It describes the lot’s condition on the test date. Up to the expiry date, the lot is expected to meet its specification when stored as required. For older lots or after long storage, a fresh test can make sense, especially with sequences prone to oxidation.
How do I check that my vial matches the CoA? Compare the lot number on the vial, the delivery note and the certificate. At Alpenpeptid you can also enter it under Verify a lot.
For laboratory research use only. Not for use in humans or animals.
