A certificate of analysis, or COA, is a lab report for one specific batch of material. A good one tells you that the vial contains what the label says, how pure it is and who tested it. Here is how to read one.
1. Lot or batch number
Start here. The lot number on the COA must match the lot number on your vial. A COA for a different batch tells you nothing about the material in your hands.
2. Identity by mass spectrometry
Mass spectrometry (MS) measures the molecular weight of what is in the sample. The COA should list the expected mass for the peptide and the observed mass, and the two should agree closely. This is the test that confirms you have the right molecule.
3. Purity by HPLC
High-performance liquid chromatography (HPLC) separates the target peptide from impurities such as shortened sequences or by-products of synthesis. Purity is reported as a percentage of the total signal. Look for the chromatogram itself, a graph with one dominant peak, rather than a number alone.
4. Net peptide content
This is the line most people skip. Peptide powder is never 100% peptide by weight. It also contains water and salt counter-ions such as acetate or trifluoroacetate left from purification. Net peptide content tells you what share of the powder is actually peptide, and it is often 70 to 90%. A vial can be 99% pure by HPLC and still contain less peptide than its gross weight suggests.
5. The testing lab and date
A COA should name the laboratory that ran the tests and the date of analysis. Independent third-party testing carries more weight than a report generated by the seller.
Putting it to use
When you reconstitute a vial, the concentration you calculate depends on how much peptide is really in it. If you need exact numbers, base your math on the verified content from the COA. Our reconstitution calculator lets you enter any vial amount, including a corrected one.