Quality, purity and COAs
Because research peptides aren't made under FDA drug-factory rules (see read 2), a lab test is the only way to know what's in a vial. That test report is a certificate of analysis, or COA.
The two tests that matter most
Mass spectrometry (MS) weighs the molecule. Every peptide has a known mass, and the main result should match it. A wrong mass means a wrong molecule, however pure.
HPLC separates what's in the sample and shows it as peaks on a chart. Purity is the share of the main peak. A real report shows the chart, not just a percentage.
Some reports also test for endotoxins (bacterial leftovers), water content, or how much actual peptide is in the vial versus salts. More is better.
A good COA vs. red flags
| ✓ Lot number | Matches the vial in your hand. A COA without a lot number proves nothing about your vial. |
| ✓ Lab name and date | An identifiable testing lab, ideally independent of the seller. |
| ✓ Both MS and HPLC | Identity and purity, with the charts. |
| ✗ "100% pure" | Real measurements always show something besides the main peak. |
| ✗ One COA for every lot | Each batch is different. The same report on every product page is a warning sign. |
| ✗ No chart, just a number | Anyone can type a number. |
Keeping it intact
A good vial can still break down if it's stored badly. Freeze-dried powder is fairly stable while it stays sealed, at room temperature and away from heat and light. More: How to store sealed peptide vials and Lyophilization: how freeze-drying preserves peptides.
Go deeper
How to read a certificate of analysis → walks through a full COA section by section. Peptide purity: what the number means → explains what a 99% figure does and doesn't tell you.
That's the end of Start here. From here, browse the peptide library.