What is a COA and how is peptide purity verified?

A certificate of analysis, or COA, reports analytical results against stated specifications. Look for the material name, lot identifier, report date, methods and actual results. Check whether the document applies to the vial being evaluated rather than a different lot or a general example.

Third-party tested. COAs available on request.

That testing statement is not a substitute for reading the report. Ask which tests were performed and how the results relate to the laboratory's acceptance criteria. A COA is evidence about the listed tests, not a universal quality guarantee.

High-performance liquid chromatography separates sample components under defined conditions. A reported purity percentage often comes from the relative areas of detected chromatographic peaks. Interpretation depends on the method, detector and integration rules.

Chromatographic purity is not necessarily the proportion of peptide in the entire vial. Water, salts or materials not detected under the method can affect total content without appearing as a simple impurity percentage. Compare the reported method and specification, not just the largest number on the page.

Mass spectrometry provides mass-based information that can be compared with the expected peptide mass. It complements chromatography because identity and chromatographic purity are different questions.

A matching mass alone does not establish every structural detail or exclude all contaminants. HPLC and mass spectrometry also do not establish sterility or endotoxin status unless those properties are separately assessed. Use the combination of documented methods required for the experiment, and retain the supporting records.