How to Read a Peptide Certificate of Analysis (COA)

A Certificate of Analysis (COA) is the lab report that accompanies a research compound. It documents the tests run on a specific batch and their results. Anyone can claim high purity; a COA is what lets you verify it. Here is what each section means.

Identity and batch information

The top of a COA identifies the compound by name and sequence, and ties the report to a specific batch or lot number. That lot number matters: a COA is only meaningful for the exact batch it describes. Always confirm the lot on the certificate matches the lot on your vial.

HPLC purity

High-Performance Liquid Chromatography (HPLC) separates the components of a sample and measures their relative proportions. On a peptide COA, the HPLC result is the headline purity figure — for example, "98.6%." That number represents the percentage of the chromatogram attributable to the target peptide versus impurities. The accompanying chromatogram should show one dominant peak with minimal smaller peaks.

Mass spectrometry (MS)

HPLC tells you how pure the sample is; mass spectrometry tells you whether it is the right molecule. MS measures the molecular weight of the peptide. The observed mass on the COA should match the theoretical mass calculated from the sequence. A match confirms identity; a mismatch is a red flag regardless of how clean the HPLC looks.

Net peptide content

A lyophilized vial is not 100% peptide by weight — it also contains residual water, counter-ions, and salts. Net peptide content (sometimes from amino acid analysis) estimates how much of the vial mass is actually peptide. It is a more advanced figure than purity, but useful when precise quantities matter.

Putting it together

• Lot number matches your vial
• HPLC purity meets the stated specification, with a clean chromatogram
• MS confirms the molecular weight matches the sequence
• Test dates are recent relative to your purchase

Keep reading