What a COA is for
A certificate of analysis documents analytical results for a specific batch. In research procurement, it is the primary trust artifact—more important than website photography or purity percentages in ads.
Identity: does the mass match?
Mass spectrometry (MS) should report a molecular ion consistent with the theoretical average or monoisotopic mass of the sequence (including expected modifications). A COA without identity testing is incomplete.
Purity: HPLC percentage
HPLC purity estimates the fraction of the main peak among detected peptide-related peaks under a method. “99%” is only meaningful with method details and a chromatogram. Different methods can yield different numbers.
Net peptide content
Lyophilized vials contain peptide plus counter-ions and residual water. Net peptide content (NPC) tells you how much actual peptide is present by weight. Dosing math in labs should use NPC, not just label weight.
TFA and salts
Many research peptides are trifluoroacetate salts from purification. TFA content can affect weight and, in sensitive biology, assay outcomes. Some vendors offer acetate exchange—document which salt form you received.
Red flags
Generic COAs reused across batches, missing lot numbers, no chromatogram, impossible masses, stock photos of spectra, or purity claims without dates. Independent third-party testing is the gold standard when stakes are high.
FAQ
Is 99% HPLC purity enough?+
It is only one data point. You also want identity confirmation, batch specificity, and preferably net peptide content. Method matters.
What is the difference between purity and content?+
Purity describes how clean the peptide peak is among related impurities. Content describes how much peptide is in the powder by mass versus salts and moisture.