Quality
How to read a peptide certificate of analysis
A certificate of analysis (COA) is a lab report for one batch of a product. For peptides, the three results that matter most are identity (is it the right molecule?), purity (how much of the material is that molecule?) and net peptide content (how much of the powder is peptide at all?). Many COAs show only the first two.
Key points
- HPLC purity is the share of peptide-related material that is the target peptide. It is not the share of the vial that is peptide.
- Mass spectrometry confirms identity by matching the measured mass to the expected one.
- Net peptide content, often 60–90%, is the figure that tells you how many milligrams of peptide are really there.
- A COA should name the batch, the testing lab and the date, and match the lot number on your vial.
The sections you will usually see
| Test | What it answers | What good looks like |
|---|---|---|
| Appearance | Does the material look right? | White to off-white powder (blue for GHK-Cu) |
| Identity by MS (ESI or MALDI) | Is this the molecule claimed? | Observed mass within about 1 Da of the theoretical mass for small peptides |
| Purity by HPLC | How much of the peptide material is the target? | Research grade commonly ≥98%; a chromatogram should be attached |
| Net peptide content | How much of the powder is peptide? | Reported as a percentage, often by amino acid analysis or nitrogen content |
| Counter-ion (acetate or TFA) | What salt is present? | Stated as a percentage; acetate is preferred for biological work |
| Water content (Karl Fischer) | How much moisture is in the powder? | Usually under 10% |
| Endotoxin (LAL) | Is there bacterial contamination residue? | Reported in EU/mg; required for anything used in cell or animal work |
Purity is not content
This is the most common misunderstanding. Say a 10 mg vial shows 99% HPLC purity and 80% net peptide content. Purity tells you that 99% of the peptide-related material is the right sequence. Net content tells you that only 80% of the 10 mg powder is peptide; the rest is counter-ions and water. The vial therefore contains about 8 mg of peptide, of which 99% is correct. If you calculate concentrations from the 10 mg label, every result is 25% too high.
Reading the chromatogram
An HPLC trace plots detector signal against time. The target peptide should be one dominant peak. Smaller peaks are impurities such as deletion sequences (missing one residue), truncated chains or oxidized forms. Purity is the main peak’s area as a percentage of all peak areas. A COA that states a purity figure without a chromatogram cannot be checked.
Reading the mass spectrum
Mass spectrometry ionizes the peptide and measures its mass-to-charge ratio. Larger peptides appear as several peaks for different charge states (for example [M+3H]3+), which the software deconvolutes to one mass. Compare the reported mass with the theoretical value for the exact sequence, including any modifications such as acetylation or amidation. A mismatch of a few daltons on a small peptide is a warning sign.
Red flags
- No lot number, or a lot number that does not match the vial.
- No testing laboratory named, or a laboratory that cannot be found.
- Round-number purities (exactly 99.00%) on every product.
- Identical chromatograms across different products or batches.
- A COA dated years before the product was made.
- Only an in-house result, with no independent third-party test.
Independent testing services will analyse a sample and report identity and purity. Some research communities pool results publicly. Those reports are useful but vary in method, so check what was tested and how.
Related profiles
- Synthetic pentadecapeptide BPC-157 BPC-157 is a synthetic 15-amino-acid peptide studied mainly for tendon, ligament, muscle and gut healing in rodents. Animal studies
- GLP-1 receptor agonist Semaglutide Semaglutide is a long-acting GLP-1 receptor agonist approved for type 2 diabetes, chronic weight management and cardiovascular risk reduction. Approved medicine
Questions
Is 98% purity good enough?
For most in vitro research, ≥98% HPLC purity is a common threshold. It still says nothing about net content, endotoxin or sterility.
What is TFA and why does it matter?
Trifluoroacetic acid is used in peptide synthesis and purification and often remains as a counter-ion. It can affect cell assays, so many researchers prefer acetate-exchanged peptides.
Can I trust a COA posted on a supplier’s website?
Treat it as a claim until you can tie it to your batch and an independent lab. Third-party testing of your own sample is the stronger check.
References
- D’Hondt M, Bracke N, Taevernier L, et al. (2014). Related impurities in peptide medicines. Journal of Pharmaceutical and Biomedical Analysis.