"99% purity" is the most repeated phrase in the peptide market - and the least understood. Here is what it actually means, how it is measured, and how to read a Certificate of Analysis like a researcher.
Identity vs purity
Quality has two independent dimensions. Identity answers "is this the molecule it claims to be?" and is confirmed by mass spectrometry, which measures molecular weight. Purity answers "what fraction of the sample is that molecule?" and is measured by HPLC, which separates and quantifies everything in the vial. A sample can have correct identity but poor purity, so both tests matter.
What 99% purity means
A 99% purity figure means that, by HPLC peak area, 99% of the material is the target peptide and 1% is everything else - truncated sequences, synthesis byproducts, or residual reagents. For research, higher purity means cleaner, more reproducible data, which is why 99%+ is the working standard for serious material.
How to read a COA
A Certificate of Analysis ties a specific lot to its test results. Look for:
- Peptide name and sequence - confirms what was tested.
- Lot number - traceability back to a synthesis batch.
- HPLC purity - the headline number, with the chromatogram if provided.
- Mass spec result - observed vs theoretical molecular weight (identity).
- Test date and lab - ideally an independent third party.
Why third-party matters
An in-house COA is the supplier grading its own homework. A third-party COA removes that conflict of interest. It is the difference between a marketing claim and a verifiable fact, and it is the standard Peptides Factory Direct holds - third-party-tested material with a COA available on request.
Red flags
- Vague "high purity" language with no number or test method.
- No lot tracking and no COA available.
- Identity claimed but never verified by mass spec.
Purity is not a marketing word - it is a measured, documented property. Treat the COA as the single most important document in any peptide purchase.
Frequently asked questions
How is peptide purity measured?
By HPLC, which separates and quantifies everything in the sample; the target peptide percentage by peak area is the purity figure.
How is peptide identity confirmed?
By mass spectrometry, which measures molecular weight and confirms the sample is the intended molecule.
What should a COA include?
Peptide name/sequence, lot number, HPLC purity, mass-spec identity, and the test date and lab - ideally third-party.
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External references: U.S. Food and Drug Administration · Peptide (Wikipedia)