A Certificate of Analysis is the document that a testing body issues after examining a particular batch of material. Most certificates are read with a single figure in mind. Almost everything that makes the document meaningful, however, is found around that figure.
What a COA is and what it is not
A COA is the record of measurements on a sample taken from a batch at a point in time. This framing marks out the limits. It is not a statement about a product line, not a certification of a supplier and not an assurance about a particular container as long as the batch identifiers do not match. It also describes the material in the condition in which it was present in the laboratory, not in the condition in which it arrives at the workplace.
Section by section
1. Identification. The header section should carry the product designation, batch or lot number, quantity or fill weight, manufacturing or analysis date as well as a structural identifier: a CAS number for a defined chemical or the sequence for a peptide. This section links the paper to the physical material. If the batch number does not match the label on the container, nothing that follows below applies to that material.
2. Methods. A robust certificate states how each result came about. For chromatographic purity this means: column, mobile phase and gradient, flow rate and detection wavelength. For identity: the mass spectrometric method used. Method conditions are what make a value reproducible.
3. Purity. Usually given as an area-normalised HPLC percentage. It is a relative measure of what the detector was able to see; water, salts and counter-ions do not appear in it. It is worth looking at the chromatogram itself, not only at the summarised value. The curve shows baseline quality, peak symmetry and whether the integration limits were set sensibly.
4. Identity. This section is skipped most often and at the same time answers the more fundamental question. Mass spectrometry reports a measured mass, which should stand next to the calculated mass, both within the stated tolerance. Purity states how much of one thing is present; identity states which thing that is.
5. Physical data and composition. Appearance, water content (typically Karl Fischer titration), counter-ion content (usually ion chromatography), net peptide content as well as solubility and storage notes for this batch.
6. Assignment and responsibility. The document should name the testing body, carry a date and be assigned to a responsible person. Whether the body is independent of the manufacturer is a material fact: an in-house result is not worthless, but it is a different kind of evidence, and the document should make clear which it is.
Purity and content are different questions
This is the most common misunderstanding. Purity answers: what proportion of the material the detector saw was the target compound? Content answers: what proportion of the mass in the container is the target compound? A batch can be high on the first value and considerably lower on the second, because water, counter-ions and residual salts take up mass without taking up purity. For quantitative work the content is the decisive figure, and it must be stated explicitly rather than derived. In detail in Understanding peptide purity.
What a COA does not do
- It says nothing about parameters that were not the subject of the test. A missing figure is an unanswered question, not a statement about the sample.
- It does not transfer to other batches.
- It does not document what happened after sampling, that is, neither transport nor storage.
- It is not proof of authenticity. It only becomes verifiable when the issuing body can confirm the assignment.
Warning signs
- No batch or lot number, or a number that does not match the label.
- A purity value without a chromatogram and without method conditions.
- No confirmation of identity, or a measured mass without a calculated mass for comparison.
- No named testing body, no responsible person, no analysis date.
- An identical document reused for several batches. That undermines the purpose of batch-specific testing.
- A low-resolution image instead of a legible, verifiable document.
Documentation context
The level before the certificate is the question of whether the document belongs to the material at hand at all. That is covered by Batch testing and traceability. The analytical methods behind the figures are described by HPLC in peptide analysis and LC-MS in peptide analysis. Batch-related documents are published under Analytics & Certificates insofar as corresponding real documents are available.
For laboratory research only. This text serves as technical information and contains no medical, diagnostic or therapeutic statements, no dosages and no application instructions for humans.
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