How to Read a Peptide Certificate of Analysis

Identifiers

A COA carries two different numbers, and they do different jobs. The report number identifies the document. The lot or batch number identifies the material that was tested. One lot can have more than one report, for example a purity test and a later retest. A single report should point to one lot.

Alongside those, look for the laboratory's name and contact details, the sample description (the material and the size as submitted), and the dates the sample was received and reported. A report missing the lot number or the laboratory is hard to rely on, however clean the numbers look.

Methods

Purity by HPLC. High-performance liquid chromatography separates the sample into its components, and a detector reads ultraviolet absorbance as they elute. Peptides are commonly read at 214 nm, where peptide bonds absorb. Purity is reported as area %: the main peak's area as a share of all the peaks detected at that wavelength.

That makes HPLC purity a relative measure. Anything that does not absorb at the chosen wavelength, or does not elute under the method's conditions, is not counted.

Identity by mass spectrometry. LC-MS or UPLC-MS measures the mass of the main component. The report should list the observed mass next to the expected mass for the sequence. Agreement within the method's tolerance supports that the material is what the label says. HPLC alone does not confirm identity, so look for both.

Results

• Purity. A figure with its method and wavelength beside it. A number with no method is a claim, not a result.
• Identity. Observed and expected mass, and a conclusion such as conforms or consistent with.
• Raw data. A chromatogram and a mass spectrum, so the result can be read rather than taken on trust.
• Identity screens. Some reports for multi-component solutions are identity screens: they list the compounds detected but not how much of each is present. Read them as a check of what is there, not a measure of amounts.
• Sign-off. The analyst or reviewer, and the date the report was issued.

Batch Matching

A report only covers the units that came from the lot it names. Check that the lot number on the vial or label matches the report exactly, and that the product name and size match too. A report for a different size, a single compound when you hold a blend, or a lot made years earlier does not cover the units in front of you.

Then verify the report with the issuing laboratory, not just the copy you were sent. Some laboratories run a verification page where you enter the report number and an access code; others let you search by lot number; otherwise, contact the laboratory directly.

The Vanta Labs COA library works this way. Reports from Kovera Labs use HPLC purity with LC-MS identity and can be checked on the lab's verify page with the report number and access code. Reports from Horizon Analytical can be searched by lot number.

Limits

A purity result answers one question: what share of the detected signal is the main component. It does not establish any of the following unless that test appears on the report:

• Peptide content or net peptide weight, which accounts for counter-ions and moisture in the material.
• Sterility.
• Endotoxin.
• Residual solvents.
• Heavy metals.
• If a test matters to your research, ask whether it was run on the lot you are buying, and ask for the report that shows it. Do not infer it from a high purity figure; each report covers the sample tested, at the time it was tested.