A Certificate of Analysis should clearly identify the material and the batch to which the reported results apply. First check the product or chemical name, batch or lot number and, where provided, identifiers such as the CAS number. Molecular formula and molar mass can provide additional verification.
This topic is closely related to Identity versus purity: what is the difference? and Which analytical method is used for chemical identification?, which provide additional context for the interpretation and characterization of chemical materials.
Pay attention to the exact chemical form. A free base, salt, hydrate or solvate may have a different formula and molar mass. A seemingly small difference in identification can therefore indicate that the document describes a different form of the substance.
A CoA is generally batch-specific. The batch or lot number on the document should therefore correspond to the material covered by the certificate. An analysis date, production date, issue date or document version can also provide useful traceability information.
A document without a clear connection to a batch provides less certainty about the relationship between the certificate and the material. Professional-looking formatting alone is not evidence of traceability.
Identity and purity answer different questions. An identity test examines whether the material corresponds to the expected chemical substance. A purity analysis examines the extent to which the analysed sample meets a particular analytical measure of purity.
A high reported purity does not automatically prove identity. Conversely, confirmed identity does not necessarily mean that the material has high purity. These aspects should be evaluated separately when reviewing a CoA.
The meaning of an analytical result depends partly on the method used. HPLC can be used to separate components in a mixture and assess relative purity. LC-MS combines chromatographic separation with mass-spectrometric information. NMR can provide extensive structural information, while FTIR can support identification through characteristic functional groups and spectra.
No single method automatically answers every analytical question. Consider whether the stated method logically supports the result being reported.
A figure such as 98%, 99% or 99.5% appears straightforward, but its meaning depends on the analytical method and the way the result was calculated. An HPLC area percentage, for example, is not automatically equivalent to the absolute mass fraction of the chemical substance in the sample.
Water, residual solvents, inorganic components or substances not detected by the chosen method may fall outside a chromatographic area calculation. Purity percentages should therefore always be read in the context of the method used.
A CoA often lists both a specification and an actual result. The specification defines the acceptance criterion, for example ≥98%, while the result gives the measured value for the particular batch.
Check whether each relevant result falls within the stated specification. Also note terms such as 'conforms', 'passes' or 'complies'. Such terms are most useful when the underlying requirement and method are clearly defined.
A useful CoA should be internally consistent. Check whether the chemical name, CAS number, formula and molar mass agree with one another and whether the analytical methods correspond logically to the reported results. Batch numbers and dates should also be consistent.
Inconsistencies do not automatically mean that the material is incorrect, but they are a reason to request clarification or additional documentation.
A CoA is a technical analytical certificate, but it has limitations. Its value depends on the representativeness of the sample, the methods used, the execution of the analysis and traceability to the batch.
A CoA should therefore not be judged by appearance alone. Logos, signatures and extensive tables may be useful for document control, but its technical value is primarily determined by the quality and coherence of the underlying analytical information.
A CoA serves a different purpose from a Safety Data Sheet (SDS) or Technical Data Sheet (TDS). The SDS mainly addresses safety and hazard information. The TDS describes general technical properties and product specifications. The CoA reports results for a specific batch.
Reviewing these documents together can help determine whether identity, product specifications, safety information and batch results are logically consistent.
A Certificate of Analysis should not be evaluated solely by its stated purity percentage. A sound review considers material identity, batch linkage, analytical methods, specifications, measured results and internal consistency. Treating identity and purity separately and interpreting results in the context of their analytical method provides a much clearer picture of what a CoA actually supports.
