A Certificate of Analysis (COA) is the single most important document when evaluating a peptide vendor. It's supposed to prove the product is what the label says it is. But not all COAs are created equal — some are genuinely useful, and others are basically marketing materials.
Here's how to read a peptide COA and spot the difference.
What a COA Should Contain
A legitimate peptide COA includes five key sections:
1. Product Identification
This should list the peptide name (or sequence), molecular weight, lot/batch number, and date of analysis. If the COA doesn't have a batch number, that's a red flag — it means you can't verify that the COA matches your specific purchase.
2. Purity by HPLC
High-Performance Liquid Chromatography (HPLC) is the standard method for measuring peptide purity. Look for:
- •Purity percentage — 98%+ is considered high quality for research peptides. 95-98% is acceptable. Below 95% is concerning.
- •Method details — C18 column, UV detection at 220nm is standard. If the method isn't specified, the result is harder to verify.
- •Chromatogram — The actual HPLC trace showing the peaks. A clean single peak at the expected retention time is what you want. Multiple peaks indicate impurities.
3. Mass Spectrometry (MS)
Mass spec confirms the molecular identity of the peptide. The observed molecular weight should match the theoretical weight within acceptable tolerances (typically ±1 Da). This is how you know the product is actually the peptide it claims to be, not a different compound.
4. Appearance and Solubility
Basic physical characterization — the peptide should be described as a white to off-white powder (for lyophilized peptides). Color changes can indicate degradation or contamination.
5. Endotoxin Testing (LAL Test)
This is the test most vendors skip, and it matters. Endotoxin contamination from bacterial cell walls can cause severe inflammatory reactions. The LAL (Limulus Amebocyte Lysate) test detects endotoxin levels. Results should be below 5 EU/mg.
If a vendor includes endotoxin testing on their COA, it's a strong quality signal. Very few vendors do this routinely.
Red Flags to Watch For
Generic COAs
If every product has the same COA template with identical formatting and the only thing that changes is the product name, be skeptical. Legitimate labs produce unique chromatograms for each batch.
No Batch Numbers
A COA without a batch/lot number is useless. You can't verify it corresponds to your purchase. It could be a COA from a single good batch applied to everything they sell.
Purity Claims Without Chromatograms
A number without the supporting data is just a claim. If a vendor says "99% purity" but doesn't show the HPLC trace, you're taking their word for it.
In-House Testing Only
COAs from the vendor's own lab are inherently less trustworthy than third-party testing. The best vendors use independent labs like Janssen, Intertek, or university analytical chemistry departments.
Old Dates
A COA from 2 years ago doesn't tell you much about today's product. Peptides degrade. Look for recent testing dates, ideally within the last 6 months.
Third-Party vs. First-Party COAs
This is the most important distinction:
- •Third-party COA: Tested by an independent lab with no financial relationship to the vendor. This is the gold standard.
- •First-party COA: Tested by the vendor themselves or their manufacturing partner. Better than nothing, but inherently biased.
In our scoring rubric, third-party COAs receive significantly higher weight. A vendor that publishes third-party lab results for every batch scores a 9-10 on COA transparency. A vendor with only first-party COAs maxes out around 6.
How We Use COAs in Our Scoring
Our COA Transparency score (30% of overall vendor score) evaluates:
- •Are COAs publicly available on the website?
- •Are they from third-party labs?
- •Do they include batch numbers?
- •How recent are the test dates?
- •Is endotoxin testing included?
- •Is the HPLC chromatogram shown (not just the percentage)?
Check any vendor's COA transparency score on their [vendor page](/vendors).
The Bottom Line
Don't buy from a vendor that doesn't provide COAs. Don't trust COAs without batch numbers. Prioritize vendors with third-party testing. And if endotoxin testing is included, that's a vendor that takes quality seriously.
For research use only. This guide is educational and does not constitute medical advice.