How to read a peptide certificate of analysis (COA)
A COA is the single most useful document a peptide supplier can give you. Here's how to read one — and the red flags that mean you should ask more questions.
A certificate of analysis (COA) is the document that connects a specific batch of a research peptide to its analytical test results. It's the difference between 'we say it's 99% pure' and 'here is the chromatogram that proves this batch is'. If you can't get a COA tied to the exact batch you're buying, you're trusting a label instead of data.
What a good COA contains
- Batch or lot number — this must match the number printed on the vial you receive.
- Product name and, ideally, the sequence and molecular formula.
- HPLC purity result, with the method (reversed-phase is standard) and usually a chromatogram.
- Mass spectrometry identity — the measured mass should match the theoretical mass of the peptide.
- Test date and the lab that performed the analysis (independent third-party testing is the gold standard).
- Net peptide content or fill weight where relevant.
Reading the HPLC result
High-performance liquid chromatography separates the compounds in a sample and reports each as a peak. Purity is the area of the main peak as a percentage of all peaks. A single, dominant peak at ≥99% with only tiny satellite peaks is what you want. Several large peaks, or a main peak well below the stated purity, means impurities or degradation.
Reading the mass spec (identity) result
HPLC tells you how pure the sample is; it doesn't by itself tell you the peak is the right molecule. Mass spectrometry confirms identity by measuring molecular mass. The observed mass on the COA should match the peptide's theoretical mass (accounting for common adducts). Purity without an identity check is only half the story.
Red flags
- No batch number, or a COA that isn't tied to a batch you can verify.
- A generic COA reused across products (the batch number never changes).
- Purity stated with no method and no chromatogram.
- No identity/mass-spec data at all.
- Testing described only as 'in-house' with no way to independently confirm it.
At Ascend Labs every batch is verified by reversed-phase HPLC and mass spectrometry at an independent lab, and the COA is published against the batch number so you can look it up before ordering and re-check the exact vial you receive.
FAQ
- What does a certificate of analysis prove?
- A COA links a specific batch to its test results — typically HPLC purity and mass-spectrometry identity — so you can confirm the product matches its label for the exact vial you receive.
- What purity should a research peptide be?
- Research-grade peptides are commonly released at ≥98–99% HPLC purity. Ascend Labs releases only batches at ≥99% with MS-confirmed identity.
- Why does mass spectrometry matter if I already have HPLC purity?
- HPLC shows how pure the sample is but not whether the main peak is the correct molecule. Mass spectrometry confirms identity by matching the measured mass to the peptide's theoretical mass.