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How to check what you are buying.

How to read a certificate of analysis, what a purity figure measures, what an out-of-specification result means, and why a lot number is what makes any of it checkable.

Last updated 2026-09-08

The certificate archive Testing methodology Common questions

Reading a certificate of analysis

Updated 2026-09-08

A certificate of analysis is a laboratory's record of what a specific batch contained. This is how to read one, section by section, and which four checks matter before you trust the number on the front.

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What HPLC purity measures

Updated 2026-09-08

A purity percentage describes the proportion of a sample that is the target compound. It is a composition measurement, not a verdict on quality, potency or fitness for use — and knowing the difference is most of what makes a certificate readable.

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Out-of-specification results

Updated 2026-09-08

An out-of-specification result means a measured value fell outside what the label claims. This archive publishes the lots that read out of specification alongside the ones that passed. Here is what the term means, and why withholding those records would defeat the point of having them.

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Why lot numbers matter

Updated 2026-09-08

A purity figure with no lot number attached cannot be checked against anything. The lot number is the join between the vial in your hand and the laboratory record that describes it, and without it a percentage is a slogan.

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None of these pages describes what a compound does, how much of it to use, or whether it is safe. Those are the questions with the most search volume in this category and they are not questions a vendor should be answering. What is here instead is the part that can be checked: what the documents mean, and how to read one before you trust it.

For laboratory and research use only · Not for human or veterinary consumption · Not evaluated by the FDA