A certificate of analysis is the primary record connecting a vial in front of you to the batch it came from. It is a document about identity and purity — nothing more, and nothing less. Knowing how to read one is the difference between a supplier claim and verified material.
Identity comes before purity
Purity expressed as a percentage is meaningless until identity is established. Mass spectrometry confirms the molecular weight of the compound matches the expected sequence. Only once identity is confirmed does a purity figure describe the right substance.
What the chromatogram shows
HPLC separates the sample into its components and reports each as a peak. The main peak is the target compound; the area under the remaining peaks is everything else. A purity figure of 98% means the main peak accounts for 98% of the total integrated area — it does not identify what the other 2% is.
Sections worth checking
- Batch or lot number — must match the vial label, or the document is not about your material.
- Test date — a COA describes the batch at a point in time.
- Method — which instrument, which column, which gradient.
- Appearance and solubility — a physical description of what you should receive.
- Laboratory identity — who performed the analysis, and whether they are independent of the supplier.
A missing section is information too
A document showing a purity number with no chromatogram, no method and no lot reference is a marketing asset, not an analytical record. Ask for the underlying data.
For laboratory and research use only. Not intended for human or animal consumption, or for any medical, diagnostic or therapeutic use. These statements have not been evaluated by the FDA.