How to read a Certificate of Analysis (COA)
A Certificate of Analysis (COA) is the analytical record for a specific batch (lot) of a reference compound. It documents identity and purity. Here is what the common fields mean and how to verify the report against the vial you received.
Batch / lot number
The batch (lot) number ties the COA to a specific production and testing run. The lot printed on your vial label should match the lot on the COA. A COA that doesn’t carry a lot number, or whose lot doesn’t match your vial, is not a batch-specific certificate. You can look up a batch at /coa.
HPLC purity
High-performance liquid chromatography (HPLC) separates a sample by its components and reports purity as a percentage of the main peak. A higher percentage indicates fewer detectable impurities. Look for a specific decimal value (e.g., 98.7%) and a chromatogram rather than a bare round number with no trace.
Identity by mass spectrometry
Mass spectrometry (MS, often ESI-MS or MALDI-TOF) confirms the molecule’s mass, which establishes identity — that the material is the intended sequence and not a different compound. Purity (HPLC) and identity (MS) answer different questions; a credible COA includes both, because a sample can read high purity on HPLC yet be the wrong compound.
Test date and lab
The COA should state when the batch was tested and by which analytical laboratory. Independent, third-party testing is more meaningful than unnamed or in-house testing. Recent, dated reports are preferable to old or undated ones.
Other analytical fields
Depending on the compound, a COA may also report water/moisture content, residual solvents, counter-ion (salt) content, and endotoxin (LAL) as a research quality-control datapoint. These describe analytical characteristics only and are not statements about any biological effect or suitability for any use beyond laboratory research.
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