How to Read a Certificate of Analysis (COA) for Peptides
A certificate of analysis is the paperwork that ties a specific batch of peptide to measured results. Knowing what each line means makes it much easier to spot a weak or unreliable document.
Key takeaways
- A COA should be tied to a specific lot number, not to a product name alone.
- Purity is normally reported by HPLC and identity by mass spectrometry.
- Missing lot numbers, missing lab names or identical results across different products are red flags.
What a COA is
A certificate of analysis (COA) reports the results of laboratory tests on a single batch (lot) of a material. For a peptide, that means the measured purity and evidence that the molecule has the correct identity. A COA is only meaningful if it is linked to the batch you actually received.
The fields to look for
- Product name and sequence or synonyms: should match the listing exactly.
- Lot or batch number: should match the vial label.
- Molecular formula and molecular weight: the theoretical values for the compound.
- Appearance: lyophilized peptides are normally white to off-white powders.
- Purity by HPLC: given as a percentage, ideally with the chromatogram attached.
- Identity by mass spectrometry: the measured mass compared with the theoretical mass.
- Testing laboratory and date: who ran the tests and when.
Checking the purity result
HPLC purity is calculated from the area of the main peak relative to all detected peaks. Look at the chromatogram if it is provided: one dominant peak with small impurity peaks is what you expect. Remember that a percentage on its own does not show how the test was run. See HPLC and mass spectrometry explained for the detail.
Checking the identity result
Mass spectrometry measures the mass-to-charge ratio of ions. The reported observed mass should agree with the theoretical molecular weight within instrument tolerance. Peptides often appear as several charge states, so a spectrum usually shows more than one peak for the same molecule.
Red flags
- No lot number, or a lot number that does not match the vial.
- No laboratory name, signature or test date.
- Identical results or identical layouts across unrelated products.
- A purity figure with no method and no chromatogram.
- A molecular weight that does not match the compound.
What a COA cannot tell you
A COA describes the batch at the time of testing. It does not describe how the material was stored or shipped afterwards, which is why correct storage and handling still matters.