How to Read a Peptide Certificate of Analysis

Which material does this report actually describe?

Before interpreting any number, establish which material the report describes. Compare the compound name and the lot or batch identifier against the product label, or against the batch being offered for purchase. A report for a different batch of the same product describes that batch, not yours. Record the issuing laboratory, the report number, and the date the testing was performed. If a reference or verification link is supplied, use it to check the original record rather than relying only on the copy you were sent.

Save the complete report alongside the purchase record, and write down any question the document itself does not answer. Presentation is not evidence: a laboratory logo, a clean layout, or a high percentage tells you nothing until the document has been matched to the material in front of you. Where the batch identifier on the report and the batch you would receive do not match, treat the report as background about the product line rather than a record of your material.

What question does each test on the report answer?

Look for separate results covering identity, purity or impurities, and assay or content. ICH Q2(R2) treats these as distinct analytical purposes, and a report that collapses them into a single headline figure has left something out. The same guideline describes specificity, accuracy, precision, and reporting range as characteristics relevant to validating a procedure for its intended use. Naming an instrument does not establish that any of those characteristics were evaluated, and it does not tell you which procedure was run on that instrument.

Use this distinction when asking for clarification. Two questions do most of the work: which method supports this result, and what can that method distinguish? A technique that separates components well may say little about the sequence, and one that confirms a mass may say little about how much of the sample it accounts for. ICH guidance is a reference for analytical principles here. It is not a claim that a research product carries pharmaceutical approval or regulatory certification.

Sources: ICH Q2(R2): Validation of Analytical Procedures (2023)

What do the units and limits on a result actually mean?

Check whether a percentage describes chromatographic signal, peptide content, or a mass fraction, because those are different quantities that share a percent sign. Peptide purity assignment can involve several independent approaches: the NIST angiotensin I study compared mass balance, amino acid analysis, elemental analysis, and quantitative NMR for exactly this reason. A number reported without its measurement basis is difficult to compare against another report, and impossible to compare confidently against a specification written on a different basis.

Ask for the stated acceptance criterion alongside the result, so you can see the limit the batch was judged against rather than the value alone. A result of 98 percent means one thing against a 95 percent limit and another against a 99 percent limit. Ask about any qualification attached to the figure, such as a value reported on an as-is basis rather than corrected for water or counter-ion content. Keep the original units in your laboratory record instead of silently converting the report into a different claim.

Sources: NIST: SI traceable purity assignment using angiotensin I

What should you do when information is missing?

A missing result is not a passing result. Work through the document against a fixed checklist: batch match, issuing laboratory, test date, method, units, numerical result, acceptance criterion, and any supporting trace or spectrum your review requires. Then ask explicitly which of the tests you expected were not performed. Reports are often assembled from the subset of work that was actually commissioned, so absence usually reflects scope rather than concealment, but either way it should remain an open question in your evaluation rather than an assumption.

For Savage Labs records, send support the compound name, vial size, batch identifier if known, and order number if applicable. Ask about document availability before ordering whenever a specific analytical record is essential to your work, rather than after the material arrives. Report availability is not implied for every product or every batch, and asking first avoids committing to material whose documentation will not meet your requirements.