Some product pages include a Certificate of Analysis (COA), which records the results of testing performed on a particular sample or batch. Read each certificate as a report on the material it identifies, not as a general guarantee covering every product or batch.
What to look for in a certificate
Start with the substance name, sample or batch identifier, date of analysis and the laboratory that issued the report. The analytical method matters too. Techniques such as NMR, GC-MS and LC-MS answer different questions, so a method suitable for confirming identity may not, on its own, quantify every impurity. Look for the reported result, units, reference standard and any stated measurement uncertainty or limitations.
For certified reference materials, the NIST explanation of certificates describes how certified values, uncertainty and metrological traceability are documented. The European Commission’s guide to reading reference-material certificates is also useful for understanding lot numbers, certified values and validity information.
What a COA cannot tell you
A result for one sample does not automatically describe another batch. A stated purity value does not establish toxicological safety, suitability for human use or legal status. Nor does a logo or accreditation claim prove that every test on the report falls within the laboratory’s accredited scope. For that, check the laboratory and the relevant scope of testing.
See Research Chemical Quality Standards for the wider quality context, and Research Chemical Safety for the limits of analytical results.