How to Read a Certificate of Analysis

A certificate of analysis (COA) is the laboratory record for one specific production lot. It states what the material is, how it was tested, which methods were used and what results were obtained. A COA describes a lot, not a product in general, so a certificate is only meaningful when its lot number matches the material you are holding.

The top of a well-formed COA identifies exactly what was tested and by whom:

• Compound name and, for peptides, the amino acid sequence.
• Molecular formula and theoretical molecular weight.
• Lot or batch number, which should appear on the container label as well.
• Date of analysis and, ideally, a retest or review date.
• The testing laboratory's name, address and accreditation (for example ISO/IEC 17025).
• A signature or approval from the person who reviewed the results.

Identity is usually confirmed by mass spectrometry (MS). The certificate should show the observed mass next to the theoretical mass calculated from the formula. Close agreement, typically within a fraction of a dalton for small peptides, indicates the main component is the intended molecule. A COA that reports purity but no identity result tells you how clean something is without confirming what it is.

Purity is most often measured by high-performance liquid chromatography (HPLC) and reported as a percentage of total peak area. A good COA includes the chromatogram itself, not just the number, so you can see the main peak and any smaller impurity peaks. See the purity and HPLC guide for what this percentage does and does not measure.

• Water content (Karl Fischer titration): lyophilized solids still hold some moisture.
• Net peptide content: the share of the material's weight that is peptide rather than water, salts or counter-ions.
• Residual solvents: traces left over from synthesis and purification.
• Endotoxin (LAL test) and microbial limits, where relevant to the intended research.
• Heavy metals and appearance or solubility observations.

• No lot number, or a lot number that does not match the label.
• No laboratory name, or a lab that cannot be found or verified.
• A purity figure with no chromatogram or method description.
• Identical certificates reused across many different lots.
• Suspiciously round results (exactly 99.0% every time) or dates long before the material was produced.

When in doubt, ask the supplier for the raw data or contact the named laboratory to confirm the report is genuine.