How to read a certificate of analysis

Certificates of analysis are cited constantly in peptide discussion and read carefully far less often. The document is a laboratory report about one batch of material, and its value depends entirely on what it discloses.

1. A batch number that ties the paper to the material

A certificate without a batch or lot number describes an unidentifiable sample. Analytical convention treats the batch identifier as the link between the report and the physical material; without it, the report cannot be verified against anything.

2. Named analytical methods

Credible reports state the technique and its conditions: reverse-phase HPLC with column, gradient and detection wavelength; electrospray or MALDI mass spectrometry for identity confirmation. A purity figure with no method attached is an assertion rather than a result.

3. The traces, not only the summary numbers

A chromatogram and a mass spectrum are the underlying evidence. Peak shape reveals shoulders, tailing and secondary components that a single headline percentage conceals. Analytical guidance from ICH and USP treats the reported trace as part of the record.

4. Who performed the analysis

In-house testing can be technically sound but is not independent. Third-party analysis means a separate laboratory with no stake in the result. Reports that identify the testing laboratory allow a reader to judge that distinction; reports that do not, do not.

5. Water and counter-ion content

This is the most common reason a stated mass and an assay result disagree. Freeze-dried peptide carries residual water, measured by Karl Fischer titration, and usually a trifluoroacetate counter-ion. Both contribute mass that is not peptide. Net peptide content, where reported, is what makes two certificates comparable.

This article concerns how to read analytical documents. It is not guidance on obtaining, handling for use, or administering any compound.

Reference materials mentioned here

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