How to read a peptide COA
5 checks. About 90 seconds. Works on any supplier’s certificate, including ours.
A certificate of analysis (COA) is the lab report for one batch of a peptide. To read it, match the batch number to your vial, compare HPLC purity to its spec, confirm identity by molecular weight, check net content against the label, and find out who ran the test.
a real released lot, straight from our library
What should you check on a peptide COA?
- 1
Match the batch number
The lot or batch number printed on your vial must match the number on the COA. That is what ties the report to the exact batch you hold. A report with no batch number describes nothing in particular.
On a real report: Lot SK10 on the vial label, Lot SK10 on the certificate. - 2
Read the purity line
Find the chromatographic purity result, usually by HPLC, and read it next to its specification. A result at or above the spec means the batch met its standard. A number with no spec beside it is hard to judge. What HPLC purity actually measures.
On a real report: HPLC-UV purity 99.82%, spec at or above 98.0%. - 3
Check identity, not just purity
Purity says how clean the sample is. Identity says what it is. Mass spectrometry compares the observed molecular weight with the theoretical weight of the labelled peptide; a match within about 1 to 2 Da confirms identity. Some labs confirm identity against a reference standard instead. Either way, the report should name the method.
On a real report: Identity by LC-MS, result Confirmed. - 4
Look at net content
Net content is the peptide mass the lab actually measured in the vial. The label claim is what the vial says. They are rarely identical. We publish net content as measured, above or below the label. Net peptide content, explained.
On a real report: 11.08 mg measured, against a 10 mg label claim. - 5
Find who tested it, or ask
A COA should tell you which laboratory ran the analysis and when. If yours does not, ask the supplier who tested it. A purity number nobody will stand behind is a claim, not a report.
On a real report: test date June 9, 2026, with the lab’s own accession number for the sample.
High purity is not proof
Lot CP10 scored 99.85% on HPLC, higher than the lot in the hero above. Then it failed identity by LC-MS. The sample was very pure, just not the compound on the label.
It did not ship. Its report stays public in our library, next to every lot that passed. A COA that shows only a purity number would have made CP10 look excellent.
What else might you see on a COA?
Not every lab runs every test. These are the lines you are most likely to meet after the five checks. Every term is defined in the peptide glossary.
Endotoxin (LAL)
A screen for bacterial endotoxin, which HPLC cannot see. Reported against a limit, often in EU/mL. Example: pass, below the 0.05 EU/mL sensitivity of the assay.
Appearance
A visual check of the vial contents. For a freeze-dried peptide this is usually “white lyophilized powder”.
Method
How each result was produced, such as HPLC-UV for purity or LC-MS for identity. A result without a method is hard to compare.
Specification
The bar the batch had to clear. Results only mean something next to their specification.
Dates
When the sample was received and when the report was issued. Older reports can still be valid for the same lot, if storage held.
Want the full picture of how we test each lot before release? See how every lot is tested.
Now try it on a real report
Every lot we have tested is public, including the ones that failed. Pick one and run the checks.
Questions about reading a COA
What is a certificate of analysis for a research peptide?
A certificate of analysis (COA) is a lab report for one specific batch, or lot, of a peptide. It lists the tests run, the method for each, the specification the batch had to meet, and the result. A COA describes the lot it was written for and no other.
What purity should a research peptide COA show?
Purity is usually reported by HPLC as a percentage. What counts as acceptable depends on the research, but the result should be shown next to its specification. Astramide does not release a lot below 98.0% HPLC purity, and publishes the report either way.
Why does a COA need identity testing if purity is high?
HPLC purity measures how much of the detected material is one main compound. It does not say which compound that is. Identity is a separate test, usually mass spectrometry. Our lot CP10 scored 99.85% purity and still failed identity, so it was not released.
How do I know a COA matches my vial?
Match the lot or batch number printed on the vial to the number on the report. If the numbers differ, or the report shows no batch number at all, the report does not describe what you hold. On astramide.com you can look up any lot number in the COA library.
What should I do if a COA does not name the lab?
Ask the supplier who ran the analysis and when. A clear, specific answer is a good sign. If nobody will say, treat the purity figure as a claim rather than a report. Some suppliers redact lab details for sourcing reasons, so asking is the fair first step.
Have a report from another supplier you want checked? Our independent testing service runs the same panel on any vial.