A certificate of analysis is a lot-specific data sheet. Read every number with its method. A headline purity without a method is not an analytical result.
Identity
The COA must repeat the name and catalog code of the purchase order. Sequence or formula, if used, must not contradict the label. If those lines disagree, the rest of the file is not usable for receiving.
Chromatographic purity
Reverse-phase HPLC with UV detection is the usual purity method for synthetic peptides. The value is typically area-percent at a stated wavelength, column, and gradient. Area-percent is not automatically weight-percent. Related-substance information, if present, belongs with the chromatogram, not in a separate marketing PDF.
Mass identity
Electrospray or MALDI mass spectrometry supports identity by matching observed m/z to the calculated mass. A mass match does not quantify purity. It answers whether the principal species is the intended sequence.
Water, counter-ion, and net peptide content
Lyophilized peptides often contain water and a counter-ion, commonly trifluoroacetate or acetate. HPLC area-percent of the peptide peak can be high while net peptide content is lower because water and salt are part of the solid. If net peptide content is claimed, the method (elemental analysis, amino-acid analysis, or a stated calculation) must appear on the file.
Batch lock
The lot on the vial, the lot on the COA, and the lot on the packing list must be the same string. A generic template without a lot number is not a COA.
Research-use and professional buyer information only. A COA is not medical guidance.