Guide
How to Read a Certificate of Analysis
What each section of a peptide COA actually proves — identity, purity, net peptide content, endotoxin and sterility — and how to match a certificate to the vial in your hand.
Why a COA matters more than a purity claim
A purity percentage printed on a website proves nothing on its own. A Certificate of Analysis is the underlying record: which lot was tested, by what method, on what date, and with what result. Compare suppliers on certificates, not on marketing numbers.
The sections of a peptide COA
| Section | What it establishes |
|---|---|
| Lot / batch number | Ties the document to the exact vial you received |
| Identity (LC-MS or MALDI) | Observed mass matches the theoretical mass of the sequence |
| Purity (RP-HPLC) | Percentage of the main peak against related substances |
| Net peptide content | How much of the vial mass is peptide versus counter-ion and water |
| Water content (Karl Fischer) | Residual moisture, which drives long-term degradation |
| Residual solvents | Trace synthesis and purification solvents |
| Endotoxin (LAL) | Bacterial endotoxin burden |
| Sterility / bioburden | Microbiological status of the filled vial |
| Appearance | Cake quality and colour of the lyophilized solid |
Matching a certificate to a vial
Read the lot number on the vial label first, then find that same lot on the certificate. A certificate for a different lot tells you about material you do not have. PX1 publishes lot records at /coa; the compound page for each product links directly to the certificate for the lot currently shipping.
Red flags
- No lot number, or a certificate that covers "all batches"
- A purity figure with no chromatogram attached
- Identity stated but no observed mass
- No issue date, or a date years older than the lot
- Testing performed only by the seller with no third-party laboratory named
Research use only. PX1 Research supplies compounds for laboratory and in-vitro research. Nothing on this page is medical advice, a dosing recommendation, or an offer for human or veterinary use.