THISTLE BIOLABS JOURNAL • ANALYTICAL TESTING
A certificate of analysis is useful when it makes a specific batch more checkable. It should be read as evidence with limits, not as a decorative quality badge.
At a glance
- The batch number should match the supplied item.
- Identity and purity are separate analytical questions.
- HPLC and mass spectrometry can provide complementary evidence.
- A COA does not establish attributes that were never tested.
Research-use note: This article concerns analytical materials supplied for controlled laboratory research. It is not clinical guidance and does not establish suitability for human or veterinary use.
A certificate of analysis (COA) is a batch-specific summary of selected test results. Used properly, it can help a laboratory confirm that the documentation supplied with a material is relevant, internally consistent and appropriate for the planned work. Used carelessly, it can become little more than a reassuring percentage.
Start with the batch, not the headline result
The most important first check is simple: the batch or lot number on the COA should match the identifier on the vial or outer packaging. A result from another batch does not describe the material in front of you.
Also check the material name, stated quantity or presentation, test date and the identity of the testing organisation. These details create the chain between the sample, the analysis and the supplied item.
Identity and purity answer different questions
Identity asks whether the principal material is consistent with the expected molecule. Purity asks how much of the detected analytical signal is attributed to the principal component rather than other detected components under a particular method.
Neither result should be used as a substitute for the other.
What an HPLC result usually represents
High-performance liquid chromatography (HPLC) separates sample components under defined conditions. Peptide COAs commonly report the main peak as a percentage of the total integrated chromatographic area.
That can be useful for comparing components detected by that method, but it is not automatically the same as mass fraction, peptide content or biological activity.
What mass spectrometry contributes
Mass spectrometry can provide evidence that detected ions are consistent with the expected molecular mass. It is often used alongside chromatography because the two techniques answer complementary questions.
A matching mass is valuable evidence, but it does not on its own establish purity, sterility, endotoxin status, concentration or suitability for a particular experiment.
What a COA does not prove
- It does not make a material sterile.
- It does not establish endotoxin or bioburden status unless those tests are specifically reported.
- It does not demonstrate safety, efficacy or suitability for human use.
- It does not replace a laboratory’s own acceptance criteria or method review.
- It does not remain representative if the batch identifier does not match.
A practical review checklist
- Match the material name and batch number to the supplied item.
- Check the test date and testing organisation.
- Separate identity evidence from purity evidence.
- Look for named analytical methods and clear units.
- Check whether chromatograms or spectra are available where relevant.
- Record any limits before deciding whether the evidence suits the intended study.
A good COA makes selected claims more checkable; it does not make every quality question disappear.
Further reading: The ICH Q2(R2) guideline covers analytical procedure suitability.
The Thistle approach
Documentation that connects to the batch
Thistle BioLabs uses supplier COAs as batch-specific analytical evidence where they accompany the supplied material. We review what the document actually reports — including batch reference, named method, identity information and reported purity — and distinguish that supplier evidence from independent third-party verification.
Continue reading
Go deeper on analytical evidence
How to read a peptide COA
What 99%+ purity means
The Thistle Standard