Two vials can look identical, carry the same label, and contain completely different things. The only way to tell them apart is a piece of paper most buyers skim past or never request — the certificate of analysis. Learn to read one properly and you gain the single most useful skill in this entire space: the ability to separate a supplier who tests from a supplier who simply claims.
This is a plain-English guide to reading a peptide COA — what each section means, which numbers actually matter, and the red flags that should make you close the tab.
What a COA is
A certificate of analysis (COA) is a lab report documenting what a specific batch of material actually contains. For a research peptide, a credible COA comes from a third-party analytical lab — not the seller’s own marketing department — and reports, at minimum, the compound’s identity and its purity. Think of it as the vial’s lab-verified ID card. Without it, every claim about what’s in the bottle is just the seller’s word.
The tests that matter
Two analytical methods do the heavy lifting, and you’ll see both named on any serious COA:
HPLC (high-performance liquid chromatography) measures purity. It separates everything in the sample and shows how much is your target peptide versus impurities. The output is a chromatogram: a big peak for the target and smaller peaks for anything else.
Mass spectrometry (MS) confirms identity. It measures the molecular weight of the compound and checks it against the known weight of the peptide you ordered. HPLC tells you how pure it is; MS tells you it’s the right molecule in the first place. You need both — a 99% pure sample of the wrong peptide is still the wrong peptide.
Reading the purity number
Purity is expressed as a percentage — the area of the target peak divided by the total area of all peaks on the HPLC trace. For research peptides, you generally want to see 98% or higher. A number in the high 90s with one dominant peak and only trace impurities is a good sign. Be wary of a COA that states a purity figure but doesn’t show the actual chromatogram: the number is only as trustworthy as the trace behind it. Also check that the batch or lot number on the COA matches the vial you received — a COA for a different batch tells you nothing about yours.
One more line worth finding: peptide content (sometimes “net peptide”). A lyophilized vial isn’t pure peptide by weight — it includes residual water and counter-ions — so peptide content tells you how much of the labelled mass is actually peptide. It’s a detail most resellers never report.
Red flags
| Sign | Credible COA | Red flag |
|---|---|---|
| Source | Named third-party lab | No lab named, or the seller itself |
| Chromatogram | Actual HPLC trace shown | A bare percentage, no trace |
| Identity test | Mass spec confirms the molecule | Purity only, no identity |
| Batch match | Lot number matches your vial | Generic or mismatched lot |
| Availability | Published or sent on request | “Trust us” — none provided |
A 99% pure sample of the wrong peptide is still the wrong peptide. Purity without an identity test is half a document.Why HPLC and mass spec go together
Why it matters
In an unregulated market, the COA is the only objective check between you and whatever is actually in the vial — mislabelled compounds, under-filled peptide content, or impurities are all real risks when testing is skipped. A supplier that publishes batch COAs openly is inviting scrutiny; that willingness is itself a quality signal. It’s why we maintain a public COA library rather than making you ask.
Pair this with how to store research peptides — even a 99% pure peptide degrades fast if it’s handled wrong after the COA was issued.
FAQ
Tap a question to reveal the answer.
What is a certificate of analysis for peptides?
A lab report documenting what a specific batch actually contains — primarily the compound’s identity and purity — ideally issued by a third-party analytical lab rather than the seller.
What purity should a research peptide be?
Generally 98% or higher, shown as one dominant peak on the HPLC chromatogram with only trace impurities. Be cautious of a purity figure quoted without the trace behind it.
What’s the difference between HPLC and mass spec on a COA?
HPLC measures purity (how much is your target vs impurities); mass spectrometry confirms identity (that it’s the right molecule by molecular weight). A complete COA includes both.
What is peptide content on a COA?
It’s how much of the vial’s labelled mass is actually peptide, versus residual water and counter-ions from the freeze-drying process. Most resellers never report it.
How do I know a COA is real?
It names a third-party lab, shows the actual chromatogram, confirms identity by mass spec, and its batch/lot number matches your vial. Missing any of these is a red flag.
Does a good COA mean a peptide is safe to use?
No. A COA verifies what a compound is and how pure it is for research use — not that it’s safe for human consumption. These are research-use-only compounds.
Should I trust a supplier with no COA?
Treat a missing or unavailable COA as a serious warning. In an unregulated market it’s the only objective check on what’s in the vial.
Related reading
References
- United States Pharmacopeia. General Chapter <621> Chromatography.
- Nguyen LT et al. Methods for peptide identity and purity assessment by LC-MS. Analytical methodology overview.
- ICH Q6A. Specifications: Test Procedures and Acceptance Criteria for New Drug Substances.