How to Read a Peptide Certificate of Analysis (COA): HPLC, Mass Spec and What to Look For
A Certificate of Analysis (COA) is the single most important document a research compound supplier can give you. It tells you what is in the vial, how pure it is, and who tested it. But a COA is only useful if you know how to read it. This guide walks through each section of a typical peptide COA and the red flags worth watching for.
1. Identification: product name, batch and dates
Every COA should clearly state the compound name, the amount per vial, a batch or lot number, and the test date. The batch number is what connects the document to the physical vial you receive, so it should match the label. A COA without a batch number, or one that is several years old, tells you very little about the product in front of you.
2. Purity: HPLC
High-performance liquid chromatography (HPLC) separates the components of a sample so they can be measured. The result is a chromatogram: a graph with peaks. The largest peak should be the target compound, and the purity figure (for example, ≥98%) is the share of the total signal that peak represents.
- Look for the chromatogram itself, not just a number. A purity figure with no graph is hard to verify.
- Check the retention time of the main peak and that the peak table adds up.
- Small secondary peaks are normal; they represent impurities such as truncated sequences.
3. Identity: mass spectrometry (MS)
HPLC tells you how pure a sample is, but not what it is. Mass spectrometry confirms identity by measuring molecular mass. The COA should list the theoretical (expected) molecular weight and the observed value. They should agree closely. A high HPLC purity with no MS data means you know the sample is pure, but not that it is the compound on the label.
4. Who did the testing
Results from an independent third-party laboratory carry more weight than in-house testing, because the lab has no stake in the outcome. A good COA names the laboratory and includes a signature or report ID you could, in principle, verify with that lab.
Red flags
- No batch number, or a batch number that does not match the vial.
- A purity number with no chromatogram.
- No mass spectrometry or identity confirmation.
- The same COA reused across many batches or many products.
- No testing laboratory named.
How PepCell handles COAs
Every PepCell batch is tested by an independent third-party laboratory in the USA, with identity and purity confirmed by HPLC and mass spectrometry. You can request the most recent COA for any compound from our Lab Reports page before you order.
All PepCell products are for laboratory research use only. Not for human or veterinary use.