Reading a certificate of analysis
What the purity figure, the mass spectrum, and the lot number on a COA actually tell you.
A certificate of analysis reports what an independent lab measured for one specific lot. The purity figure comes from HPLC and states the fraction of the sample that is the target peptide. The mass spectrum confirms the molecular weight matches the expected sequence. The lot number ties the document to the vial in your hand.
Why lot-level matters
Two lots of the same compound can differ. A COA per lot, published before the lot is sold, is the only documentation that describes the material you receive rather than the product in general.