How to read a peptide certificate of analysis
A certificate of analysis (COA) is the lab report for one specific batch of material. It is the only document that tells you what is actually in a vial, and it is worth knowing how to read one before you rely on it.
1. Identity: is it the right molecule?
Identity is usually confirmed by mass spectrometry (MS). The report lists a theoretical (expected) molecular weight and an observed mass. They should agree closely, typically within about one dalton for a peptide of this size. A COA that reports purity but no identity result tells you something is pure, but not what it is.
2. Purity: how much of it is that molecule?
Purity is usually measured by high-performance liquid chromatography (HPLC) and reported as a percentage. That number is the area of the main peak divided by the total area of all peaks detected. A good COA includes the chromatogram itself, not just the number, so you can see the main peak and any smaller impurity peaks.
3. Lot number and date
The lot (batch) number on the COA should match the lot number on your vial. A COA for a different lot describes different material. The test date tells you how recent the analysis is.
4. Who tested it
Look for the name of the testing lab. An independent third-party lab has no stake in the result. Accreditation such as ISO/IEC 17025 means the lab's methods and quality system have been audited.
What a COA usually does not tell you
- Net peptide content. HPLC purity says how much of the peptide material is the target sequence. It does not say how much of the powder's weight is peptide versus residual water and counter-ions.
- Sterility and endotoxin levels. These need separate tests and are only covered if the COA lists them.
- Anything about other batches. Each COA covers one lot.
Red flags
- No lot number, or a lot number that does not match the vial.
- Purity reported with no chromatogram, or a suspiciously perfect 100.00%.
- No identity (mass spec) result.
- No lab name, no date, or the seller's own name as the testing lab.