How to Read a Certificate of Analysis

Four fields that decide the document — Identity, purity, method and lot number. A certificate carrying all four supports a goods-in release. A certificate missing any one of them requires a follow-up request, which is precisely what a certificate is meant to avoid.

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Identity — Identity is normally confirmed by mass spectrometry, comparing the observed molecular weight against the theoretical value for the intended structure. The useful information is the observed value, the theoretical value and the deviation, not a bare statement that the material conforms.

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Purity — Purity is normally determined by reverse-phase HPLC and reported as area percentage at a stated wavelength. Area percentage is a measurement of peak area, not a mass balance, so a high figure does not by itself describe what the remaining percentage contains.

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Method — Method conditions determine whether a purity figure means anything. Column dimensions, stationary phase, gradient, flow rate, detector wavelength and run time should all be recorded. Without them, a purity figure cannot be compared with a figure produced under different conditions.

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Lot number — The lot number links the document to the physical unit received. A certificate that references a different lot from the delivered unit does not support the release of that unit, even if every other field is correct.

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The remaining fields — Appearance, specification limits, release date and the name of the releasing analyst complete the document. Specification limits state what the batch was released against; the releasing analyst establishes accountability. Where a result is close to a limit, the decision rule applied is worth asking about explicitly.

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