Guide · 6 min read
Peptide COA vs certificate of purity: what to look for
Vendors use several names for their testing paperwork: Certificate of Analysis (COA), certificate of purity, purity report, certificate of conformance, "lab results". They are not interchangeable. This guide explains what each one usually contains, which ones actually prove identity, and what to ask for.
Short answer: a COA reports measured results for a specific batch, ideally identity and purity. A certificate of purity often reports only a purity percentage, which can't tell you whether the vial holds the right compound.
What a Certificate of Analysis is
A Certificate of Analysis is a batch-level test report. A complete peptide COA normally includes:
- Identification: product name, batch or lot number, and sample or report ID.
- Identity result: a mass spectrometry value that can be compared with the compound's theoretical molecular weight.
- Purity result: an HPLC purity percentage with chromatogram and peak table.
- Method details: techniques, and ideally columns, wavelengths and instruments.
- Provenance: the testing lab's name, the test date, and a way to verify the report.
- Optional extras: content per vial, endotoxin, sterility, heavy metals, counter-ion such as TFA.
Step through each section in how to read a peptide COA.
What a "certificate of purity" usually is
There isn't one agreed definition of "certificate of purity" for research peptides. In practice it is used for documents ranging from a full COA under a different name to a one-line statement such as "Purity: 99.2% (HPLC)". What it tends to lack:
- No identity test. Purity is reported, but there is no mass spectrometry result. A pure sample of the wrong peptide would produce the same document.
- No chromatogram. Just a number, with no way to see the peaks behind it.
- No batch link. A generic product-level statement rather than a report for a specific lot.
- No lab. Issued by the seller or manufacturer, with no independent testing lab named.
If a "certificate of purity" contains all the elements of a COA listed above, treat it as a COA and check it the same way. The name matters less than the contents.
Side-by-side comparison
| Element | Full COA | Typical certificate of purity | Certificate of conformance |
|---|---|---|---|
| Batch-specific | Yes | Sometimes | Sometimes |
| Identity (mass spec) | Yes | Often missing | Usually not |
| HPLC purity % | Yes | Yes | Sometimes, as a specification ("≥98%") |
| Chromatogram and spectra | Yes | Often missing | No |
| Testing lab named | Yes | Often missing | Usually the manufacturer |
| Verifiable report ID | Ideally | Rarely | Rarely |
| Measured results or a promise? | Measured | Measured (purity only) | Promise of meeting a spec |
Specification vs result
One subtle trap: a document can list a specification ("Purity: ≥98.0%") without a result ("Purity: 99.1%"). A specification is the target, not proof the batch met it. Good COAs show both, often in "Specification" and "Result" columns. If you only see thresholds and the word "Conforms" or "Pass", ask for the measured values and the data behind them.
Why identity matters more than purity
Purity answers "how much of this sample is one thing?" Identity answers "is that thing the right compound?" Both matter, but identity comes first. A 99.5%-pure vial of the wrong peptide is still the wrong peptide. Mass spectrometry provides identity evidence by comparing the measured mass with the theoretical mass, including charge-state ions such as [M+2H]2+. See mass spectrometry explained for the details, and what a good HPLC purity is for interpreting the purity number.
What to ask a vendor for
If you only have a certificate of purity or conformance, a polite request covers it:
- The full Certificate of Analysis for the batch you will receive, as the original PDF.
- The mass spectrometry result and spectrum, not only the HPLC purity.
- The HPLC chromatogram with its peak table.
- The name of the testing lab and a report ID you can verify with it.
A vendor with real data can usually send this quickly. If they can't, you have learned something useful. Then use the vendor COA checklist to score what they send.
Not sure what your document proves? Enter what it shows and the checker will flag what's missing.
Open the COA checker →Sources
- PubChem (U.S. National Library of Medicine): Reference formulas and masses used to check identity results.
- ISO/IEC 17025:2017: Standard covering how testing labs report results.
- PeptideCOACheck methodology: What the checker requires from a COA.
Last updated . Written and maintained under our editorial policy. Found an error? See corrections.
Frequently asked questions
Is a certificate of purity the same as a COA?
Not necessarily. There is no single standard definition of a certificate of purity in the research-peptide market. It often states only a purity percentage. A full Certificate of Analysis reports the actual test results for a batch, normally including identity by mass spectrometry and purity by HPLC, with the method, lab and date.
Does a certificate of purity prove a peptide is what the label says?
Usually not. A purity percentage says how much of the sample is one main component, not which compound that is. Identity needs a mass spectrometry result that matches the compound's reference mass.
What should I ask for if a vendor only offers a certificate of purity?
Ask for the full batch COA with the mass spectrometry result, the HPLC chromatogram and peak table, the batch number, test date and the name of the testing lab, plus any report ID you can verify with that lab.
What is a certificate of conformance?
A certificate of conformance (or compliance) is a statement that a product meets a specification. It may not include any measured data. It is a promise, not a test report.
Can I run a certificate of purity through the COA checker?
Yes. Enter what it contains. The checker will flag what's missing, such as the mass spectrometry result or lab name, so you can see what to ask for.
Educational content only. Not medical advice. Research peptides are sold for laboratory research purposes only.