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How to Read a Certificate of Analysis (COA)
Posted by Marcus Chen | Pinned
A Certificate of Analysis is the single most important document you'll never read — until now. It's the lab report card for your peptide, and if you're not checking it, you're flying blind.
Think of it this way: you wouldn't buy a used car without a Carfax report. A COA is the Carfax for your peptide. It tells you what's actually in that vial, how pure it is, and whether it's going to do what you think it's going to do.
What a COA Is
A COA is a document provided by the manufacturer or a third-party lab that details the testing results for a specific batch of peptide. Every batch should have one. If you can't get a COA for the specific batch you purchased, that's problem number one.
Key Sections to Look At
1. Peptide Identity / Sequence Confirmation
This confirms the peptide is actually what the label says it is. Methods used are typically mass spectrometry (MS) or HPLC-MS. You're looking for the molecular weight to match the expected value for that peptide sequence.
If the molecular weight is off by more than 1-2 daltons, something's wrong. Either it's the wrong peptide, or there are significant impurities.
2. Purity (HPLC)
This is the big number everyone looks at. It's expressed as a percentage, determined by High-Performance Liquid Chromatography.
• >98% — Pharmaceutical/research grade. This is what you want.
• 95-98% — Acceptable for most research purposes.
• <95% — Ask questions. What's the other 5%+? Degradation products? Synthesis byproducts?
• <90% — Walk away.
A vendor advertising "99% purity" but the COA says 96%? That's not a rounding error. That's dishonesty.
3. Endotoxin Testing (LAL Test)
Endotoxins are bacterial toxins that can cause fever, inflammation, and worse. The Limulus Amebocyte Lysate (LAL) test measures these. You want to see:
• <5 EU/mg — Standard acceptable level
• <1 EU/mg — Even better
If there's no endotoxin data on the COA, that's a yellow flag. For injectable peptides especially, this test is non-negotiable.
4. Heavy Metals / Residual Solvents
Some synthesis processes use chemicals like TFA (trifluoroacetic acid), DMF, or acetonitrile. A good COA will show residual solvent testing with levels well below safety thresholds. Heavy metals (lead, mercury, arsenic) should be tested and below USP limits.
No solvent or metals data? Another flag.
5. Appearance / Physical Description
Should match what you received. White to off-white lyophilized powder is standard for most peptides. If the COA says white powder but you got a yellow cake, something happened between lab and delivery.
6. Water Content (Karl Fischer)
Lyophilized peptides should have very low moisture content — typically <5%. High moisture means potential degradation and shorter shelf life.
Red Flags That Mean a Vendor Is Sketchy
• No batch number on the COA. A generic COA that applies to "all batches" is worthless. Every batch varies.
• Suspiciously round numbers. Purity of exactly 99.00%? Every single test at the exact threshold? Real lab data has decimals and variation.
• No lab name or accreditation. Who ran these tests? A reputable COA includes the testing lab, analyst name or ID, and date.
• Missing tests. A COA with only purity and nothing else? That's a half-done job.
• COA doesn't match your batch/lot number. Always cross-reference.
• They won't provide one at all. This is the biggest red flag of them all.
If a vendor won't provide a COA, run. Not walk. Run. There is zero legitimate reason for a peptide vendor to withhold testing data. None. "We're waiting on the lab" for more than a few days is an excuse. "We don't do third-party testing" is a confession.
How to Request a COA
Email the vendor with your order number and ask for the COA specific to your batch/lot number. A good vendor will have it available on their website or send it within 24 hours. Some will even include it in the package.
Third-Party Testing
If you really want to verify, you can send a sample to an independent lab for testing. Companies like Janoshik and others offer peptide testing services. It costs money, but it's the gold standard for verification.
The COA isn't just paperwork. It's the difference between knowing what you have and guessing. Read it every time.
— Marcus
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How to Read a Certificate of Analysis (COA)
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