How to read a peptide Certificate of Analysis (COA)
A Certificate of Analysis is the single most useful document in this market, and the one most buyers never actually read. It is a lab report that says what a specific batch of material is and how pure it tested. Here is every section that matters, what it proves, and, just as important, what it doesn't.
The header: identity and traceability
- Product name and sequence. The peptide's name and often its amino acid sequence or molecular formula. This is what the lab tested against.
- Lot or batch number. The most important line for you personally. A COA describes a batch; this number is how you confirm the document belongs to the material you received. If your vial's lot doesn't match, the COA isn't yours.
- Testing lab and date. Who ran the tests and when. An independent, named third-party lab is worth far more than "tested in-house."
Purity: usually by HPLC
The headline number, often shown as something like "≥99%," comes from High-Performance Liquid Chromatography (HPLC). HPLC pushes the dissolved sample through a column that separates the target peptide from synthesis byproducts and impurities. Each compound shows up as a peak; the area of the main peak relative to the others gives the purity percentage.
What to look for: a clean chromatogram with one dominant peak, the purity value, and the method noted. What it means: a relative measure of how much of the sample is the intended peptide under that method. What it does not mean: anything about biological activity. Purity is a chemistry measurement, full stop.
Identity: usually by mass spectrometry
Purity tells you the sample is mostly one thing; it doesn't by itself tell you that thing is the right peptide. That's what mass spectrometry (MS) is for. MS measures the molecular weight of the compound and compares it to the expected weight for that exact sequence. A match confirms identity. A strong COA shows both: HPLC for how pure, MS for what it is.
Net peptide content (the line people miss)
Purity and net peptide content are different numbers. A vial can be highly pure yet contain bound water, counter-ions, or residual salts from synthesis, so the actual mass of peptide can be lower than the label weight. Some COAs report net peptide content separately. It doesn't make the material "worse," but it's useful context when you're comparing vendors precisely.
Safety-adjacent tests
- Microbial / bioburden. Checks for microbial contamination. Peptide synthesis uses harsh solvents inhospitable to microbes, so clean results are normal for properly handled material.
- Endotoxin. Measures bacterial cell-wall fragments. Relevant for material handled to a high standard.
- Water / residual solvent. Sometimes reported; high residual solvent can indicate rushed drying.
The step almost everyone skips: verify it
A COA is a PDF, and PDFs can be edited. The three checks that turn a document into evidence:
- Independent lab. Is the testing lab a third party, not the vendor itself?
- Lot match. Does the lot or batch number on the COA match your product's lot?
- Verification link. Does the lab offer a lookup or verify link so you can confirm they issued that exact certificate and it hasn't been altered? The better testing labs do.
If all three hold, you have real evidence. If any is missing, treat the number as a claim, not a measurement.
What a COA can and can't do
A COA can
A COA can't
Scope
Document purity and identity of a tested batch.
Prove anything about an untraceable individual vial.
Meaning
Show the material is what it claims to be, chemically.
Say anything about biological or health effects.
Trust
Be verified with the issuing lab when a link is provided.
Be trusted blindly if it's in-house or unverifiable.
Research use only. A certificate of analysis is a chemistry document. It says nothing about use in humans or animals, and this article makes no such claims. Statements have not been evaluated by the FDA. Every Sol Peptides order includes its lot's COA on request.
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