Understanding Certificates of Analysis (COAs)

A real COA is a one or two page PDF issued by the testing lab. It names the compound, lists the batch code, shows the HPLC chromatogram with the main peak, reports purity as a percentage of total area, shows the mass-spec spectrum confirming the molecular weight, and ends with the lab's signature and date.

Match the batch code on the PDF to the batch code printed on your vial. Confirm the molecular weight on the mass-spec page matches the theoretical weight for that peptide. Look at the chromatogram — there should be one dominant peak with minor noise, not multiple competing peaks.

No batch code. No lab name or signature. 'Purity report' that is actually just a screenshot. Chromatogram missing entirely. Purity reported without HPLC method. Same COA reused across multiple batches.

The chromatogram is where a COA stops being a summary and becomes evidence. Three features deserve attention. The main peak's retention time should sit where the method's reference standard places it — a shifted peak can indicate a different compound or a column problem. The integration baseline should be flat between peaks; a wobbling baseline inflates or deflates the purity number without changing the chemistry.

The related-impurities panel is the honest part of the report. A 99.2% main peak with a single identifiable 0.6% impurity tells a different story from a 99.2% main peak spread across six unnamed minor peaks. Methodology also matters: the report should state the column type, mobile phase and detection wavelength, because the same sample can read differently across methods.

One habit separates careful readers from casual ones: check that the chromatogram's date matches the report date, and that the batch number on the report matches the one on the vial — not a batch from the previous production run.

A certificate is a snapshot of one sample from one batch at one point in time. It cannot speak to storage conditions after the batch left the laboratory, to how the vial was handled in transit, or to what happens once the material is reconstituted. Those phases belong to the receiving laboratory's handling protocol, not to the supplier's documentation.

It also cannot certify sterility unless sterility testing was actually performed and stated — most research-grade COAs do not include it. And it cannot vouch for compounds not on it: a certificate for batch A says nothing about batch B, even from the same synthesis campaign. That is why each batch carries its own report rather than a campaign-level summary.