Certificate of Analysis: What It Does and Does Not Say

A certificate of analysis is evidence of what was tested. That is less than “everything”, and that honesty is exactly what makes it useful.

A Certificate of Analysis (CoA) is the document that accompanies a batch of research material and records the results of the tests performed on it. It is one of the most valuable documents in the lab, and at the same time one of the most overestimated. A CoA proves precisely what it states, and nothing beyond that. Keeping that clearly in view is what lets the certificate serve its purpose, without it being leaned on for questions it does not answer.

What a CoA contains

A complete CoA for a synthetic peptide has a fixed core. It states the identity of the substance and the measured molecular mass, usually confirmed by mass spectrometry. It gives the chromatographic purity, most often by HPLC, with the method noted. It records the appearance of the material, the batch or lot number, the production or test date, and, where determined, the water content and residual solvents.

Each of these fields is a measurement with an acceptance limit. Purity is tested against a threshold; mass against the theoretical value of the sequence. In a well-designed quality system those limits are set in advance, not adjusted afterwards to fit the result (Lian et al., 2021). A CoA is in that sense a snapshot: it describes this batch, measured with these methods, at this point in time.

What a CoA does not prove

The boundary of a CoA lies at what was not tested. A certificate that reports purity and identity says nothing about sterility, unless a sterility test was explicitly performed and stated. It says nothing about endotoxins if no endotoxin test appears on it. And it says nothing about the suitability of the material for a specific application; that is a judgement the researcher makes, not a property a certificate can establish.

There is a subtler boundary as well. A purity percentage shows only the impurities the method makes visible. Counterions such as trifluoroacetate, which binds to the peptide as a salt during synthesis, do not automatically appear on a standard HPLC purity measurement yet do affect the actual peptide content (Erckes et al., 2025). A CoA that reports purity without the counterion form or a content determination leaves that question open. That is not a flaw in the document. It is the reason to read exactly what is and is not on it.

The core rule is simple: a CoA is evidence of the tests performed, not of the absence of everything that was not tested. Absence of an entry is not evidence of absence of the problem.

Lab data versus independent verification

A lab certificate is the producing laboratory's analytical data. It is a valuable starting point, but it is a statement by one party about its own product. The question is not whether a lab can be trusted, but whether a research setting wants to rely on a single unverified source alone.

This is where Peptalis draws its distinction. Peptalis obtains peptides from specialised laboratories and manufacturers and requires extensive analytical lab testing as part of selection: identity by mass spectrometry, purity by HPLC, with the accompanying documentation. That lab data is the first layer. Then comes an internal assessment following a fixed procedure: checks on identity, purity and stability, visual inspection and vial integrity, and where relevant a reconstitution test. Only when those steps hold does Peptalis issue its own Certificate of Analysis on its own letterhead, combining the lab data with the Peptalis verification layer, signed by the Peptalis Research Team. Where Peptalis sees reason to, a batch can additionally be tested at an independent European laboratory; that report is an internal control instrument, not a seal of approval. A batch that does not meet the standard is rejected and does not enter the catalogue.

The lab certificate itself stays an internal source: it underpins the release, but it is not the document that travels with an order. What the buyer receives is Peptalis's own CoA, in Dutch or English. What Peptalis has verified itself is shown as such; what it has not established itself is named. That is the difference between letting data exist and adding verification to it.

How to read dates and batch numbers

Two fields on a CoA connect the paper to the vial in hand: the batch number and the date. The batch number links the certificate to a specific production and testing round. That same number should reappear on the vial label, so that certificate and material belong together unambiguously. If the number differs, the certificate does not belong to this vial.

The date places the measurement in time. A purity measured on the test date is a statement about that moment; storage conditions in the time afterwards fall outside that measurement. At Peptalis, every order ships as standard with the own Peptalis CoA (the release report, in Dutch or English), the batch number and the storage conditions, so that the chain from vial to batch to test date to document can be followed; the underlying lab certificate remains an internal source. A certificate without a traceable batch number or date loses exactly that: the link that makes it useful.

Registered nurse with eleven years in psychiatry and founder of Peptalis. Writes the platform's knowledge layer: compound profiles, evidence reviews and the quality methodology. Works from primary literature (PubChem for chemistry, PubMed for studies) and states where evidence is absent.

Sources checked via PubMed · 2 references

• What a CoA contains
• What a CoA does not prove
• Lab data versus independent verification
• How to read dates and batch numbers

• Lian et al. 2021 ↗
• Erckes et al. 2025 ↗

• In DepthHPLC purity vs. peptide content: what is actually being measured?
• In DepthBatch testing vs. lab documentation: where is the difference?

Compounds in this article

• Epitalon · In stock · Batch PEP-EPI-2026-01 · HPLC 99.11% · released 2 Jun 2026 · Research profile · View in catalogue
• TB-500 · In stock · Batch PEP-TB5-2026-01 · HPLC 98.65% · released 31 Aug 2026 · Research profile · View in catalogue

For laboratory research use only. Not for human use.

SCIENTIFIC REFERENCES

These references are provided for informational and research purposes only. They do not constitute medical advice.

1. 01Review / MethodCharacterization of Synthetic Peptide Therapeutics Using LC-MS.Lian Z, Wang N, Tian Y, Huang L. J Am Soc Mass Spectrom. 2021;32(8):1852–1860.Methodological review of LC-MS characterisation for synthetic peptide therapeutics; it establishes what a CoA can and cannot conclude from the reported identity and purity measurements.View on PubMed →
2. 02Method / AnalyticalTowards a Consensus for the Analysis and Exchange of TFA as a Counterion in Synthetic Peptides.Erckes V, et al. Pharmaceuticals (Basel). 2025;18(8):1163.Consensus-oriented analysis of TFA counterions in synthetic peptides; shows why a purity number alone leaves counterion content, and therefore actual peptide mass, unaddressed on a CoA.View on PubMed →