What does 99% peptide purity mean?
Short answer · as of 2026-10-05
A purity percentage is the result of a particular test method on a particular sample. EMA's guideline describes purity as control of total and individual impurities, separate from assay (amount). So “99%” with no method, limit or chromatogram cannot be interpreted, and it does not say how much peptide is present, whether it is the right compound, or whether it is sterile or safe.
By Peptide Industry Gossip · Published · General explanation, not legal or medical advice. Disclaimer.
What the number is
EMA's synthetic-peptide guideline controls purity as total and individual impurities by a stated method, with a separate assay for content and separate identity testing. A purity figure depends on the method used to produce it.
What to check behind it
- The method named, and whether a chromatogram is attached or available on request.
- The limit the result was held to, since WHO's model pairs each result with acceptance criteria.
- An identity result, a content result and the other tests the report lists or omits.
- The sample and lot, and whether the lab is accredited for that test.
Why the claim deserves care
A 2015 peer-reviewed study bought 98 synthetic peptides ordered at 95% purity or higher and found only 44.0% met the required purity, with a large discrepancy between supplier COAs and the authors' own quality control. These were research suppliers in 2015, not the current retail market. The finding is about the gap between claim and measurement, not about any one number.
What it does not tell you
- The amount of peptide in a vial.
- Whether the product is sterile or low in endotoxin.
- Whether it is safe or suitable for human use. We do not say what purity counts as acceptable.
Sources
- EMA, Guideline on development and manufacture of synthetic peptides (adopted Dec. 4, 2025)
- WHO, Model certificate of analysis
- Verbeke et al., Quality evaluation of synthetic quorum sensing peptides used in R&D, J Pharm Anal 2015