The term "Certificate of Analysis" is used widely in the research peptide supply chain, but it is not always used correctly. Sellers attach PDFs to product pages and call them COAs. Manufacturers include sheets in shipments labelled as such. The documents range from genuinely rigorous analytical records to single-page print-outs with a purity percentage and nothing else. Knowing what a real COA must contain — and why each element matters — makes the difference between having evidence and having a paper impression of evidence.
This article defines a COA in formal terms, explains its four core components, and draws a clear boundary between documents that can support a verification decision and those that cannot.
The COA as a Laboratory Record
In pharmaceutical and chemical quality control, a Certificate of Analysis is a formal document issued by a testing laboratory reporting the results of specific analytical tests performed on a defined sample. The key word is specific. A COA does not describe a compound in general; it describes the test results for one production batch of that compound, identified by a lot or batch number, analysed on a stated date, by a named testing facility.
This specificity is what gives a COA its evidential value. Two batches of the same peptide, synthesised under similar conditions by the same supplier, can differ in purity, impurity profile, water content, and microbial load. A document that reports test results for one batch cannot logically be applied to another. When a document lacks a batch number, or when the same document appears across many different products with different lot numbers, it has ceased to function as a COA in the analytical sense — it has become a template dressed as a record.
The issuing party also matters. A COA is issued by the laboratory that performed the analysis, not by the entity that manufactured or sold the peptide. When a vendor produces its own certificate covering its own product, it is grading its own work. This is not verification; independent analysis means the testing laboratory has no commercial stake in the result. Organisations including the World Health Organization and ISO/IEC 17025 — the international standard for testing and calibration laboratories — are built around this principle: the independence and competence of the testing body is the foundation of the result's credibility.
The Four Core Components of a Genuine COA
A complete, genuine COA for a synthetic peptide contains four categories of information. Each is necessary; none is sufficient on its own.
The lot number or batch number on a COA is the link between the document and the physical material. It should appear on the COA and match exactly the identifier printed on the vial label or product packaging being supplied. This match is the chain of custody: it is what allows a researcher to say, "this document describes the material in this container."
Without a batch number, or with a batch number that does not correspond to the supplied material, there is no chain of custody. The analytical results in the document belong to some unknown batch — or to no real batch at all. In practice, the lot number should be requested and confirmed before relying on any other content of the certificate.
The COA must name the laboratory that performed the tests. This means a real business name distinct from the seller, a physical address, and contact information. Where the laboratory holds accreditation under ISO/IEC 17025 — the internationally recognised standard for the technical competence and impartiality of testing laboratories — the accreditation number should be stated so it can be verified with the issuing accreditation body.
ISO/IEC 17025 accreditation means the laboratory has been audited against defined criteria covering method validation, instrument calibration, staff competence, and quality management. A result produced under these conditions is not merely a number — it is a number backed by a documented system of controls. The European Medicines Agency references pharmacopoeial methods and independent laboratory standards as part of its quality framework for medicinal substances. The same principles of independent, method-validated testing apply to research materials.
When a COA carries only the seller's logo and no independent laboratory name, the attribution test fails immediately. No further analysis is necessary; the document cannot be treated as independent analytical evidence.
High-Performance Liquid Chromatography (HPLC) is the standard technique for measuring the purity of a synthetic peptide. The method works by dissolving the sample and passing it through a chromatographic column under pressure. Different compounds interact with the column's stationary phase to different degrees and elute — exit the column — at different time points. A UV detector positioned at the column outlet records absorbance as each compound passes, producing a chromatogram: a plot of UV absorbance over time.
The purity figure is derived from this chromatogram by integration. The area beneath each peak in the trace is calculated, and the area of the main peak — the target peptide — is expressed as a percentage of the total integrated area across the run. A purity of 98% means that 98% of the UV-absorbing material detected in the injection belongs to the main compound; the remaining 2% is attributable to impurities such as truncated sequences, deletion peptides, or protecting-group residues from the synthesis process.
This figure is only meaningful when accompanied by the chromatogram itself. A bare percentage — a number on a line with no trace attached — is a claim, not evidence. The chromatogram allows a reader to inspect the main peak shape, its integration limits, the height of any shoulders or adjacent minor peaks, and the baseline stability. Without it, there is no way to assess whether the integration was performed correctly, whether an impurity peak was deliberately excluded, or whether the value reflects real data at all.
The United States Pharmacopeia (USP) general chapter <621> on Chromatography provides the methodological framework for HPLC analysis that most independent laboratories follow. For research-grade synthetic peptides, a purity of ≥98% by HPLC is the commonly cited benchmark in the scientific literature.
Purity analysis by HPLC measures the proportion of material at a given retention time but does not confirm what that material is. A synthetic peptide with 99% HPLC purity could, in principle, be the wrong sequence entirely — a structurally similar compound that elutes in the same window and absorbs UV light similarly. Mass spectrometry closes this gap.
Liquid Chromatography-Mass Spectrometry (LC-MS) combines chromatographic separation with mass-based detection. After the compound elutes from the LC column, it enters the mass spectrometer, which ionises the molecules and measures their mass-to-charge ratio (m/z). For each peptide, the exact molecular mass can be calculated from its amino acid sequence and any modifications. The spectrometer reports the observed mass, and the COA should present both values — theoretical and found — side by side. Agreement between them (typically within defined tolerances depending on instrument resolution) confirms that the compound is what the label states.
The COA should include the mass spectrum: the plot of ion intensity against m/z values, showing the observed ion peaks with their charge states identified where relevant. A result reported as "identity confirmed" with no spectrum is again a claim rather than evidence. Without the spectrum, the numerical agreement between theoretical and found mass cannot be independently assessed.
Together, HPLC purity and LC-MS identity provide the two complementary axes of analytical confirmation: how much of the target compound is present, and whether the compound is the correct one. A COA that provides only one of these two analyses is incomplete as an identity and purity record.
Genuine COA versus Generic or Recycled Document
The distinction between a genuine COA and a document that merely resembles one comes down to one question: can this document be traced to the specific batch of material being supplied?
A generic document is one that covers a compound in general, without reference to a specific production lot. It may contain real analytical data — possibly from a past batch or from a reference sample — but it cannot tell a researcher anything about the material in a current shipment. Generic COAs are sometimes produced to establish a product's general quality profile and then reused unchanged across many different transactions. The analytical data may be accurate for some batch, but it is not the batch being sold.
A recycled document is one that carries a lot number but has been applied to different batches over time without being re-issued for each. The clearest indicator is an analysis date that is inconsistent with when the supplied batch was manufactured — for instance, a certificate dated two years before the batch was synthesised. Another indicator is the same document appearing with identical data across multiple nominally different lot numbers from the same seller. Recycling a COA is the analytical equivalent of submitting an old test result as a new one.
Both failure modes — generic and recycled — result in the same practical outcome: the researcher has no verified information about the material in hand. The document exists but does not answer the relevant question.
Net Content and What HPLC Purity Does Not Capture
A point that is easy to overlook: HPLC purity tells you the proportion of the target peptide relative to other UV-absorbing material in the sample. It does not tell you the absolute mass of peptide in the vial, because lyophilised peptides always contain residual water from the freeze-drying process.
Water does not absorb UV light at the wavelengths used in standard HPLC detection, so it is invisible to the chromatogram. A vial nominally containing 10 mg of peptide at 98% HPLC purity and 10% water content actually contains approximately 8.8 mg of anhydrous peptide mass. The gap between the labelled amount and the true net peptide content is not captured by HPLC alone.
This is why complete COAs include water content measured by Karl Fischer titration, as referenced in USP general chapter <921>, and bacterial endotoxin measured by LAL assay. These additional analyses complete the picture of what the vial actually contains. A COA that reports only HPLC purity — even a real chromatogram with a genuine lot number — leaves the net peptide content and endotoxin load uncharacterised.
What a COA Does Not State
A Certificate of Analysis is an analytical record, not a clinical or regulatory document. It does not state therapeutic indications, does not describe safety in humans, and does not constitute regulatory approval of any kind. The peptides covered by COAs in the research context are, depending on jurisdiction, either unscheduled research chemicals or regulated pharmaceutical substances — the legal classification varies significantly between countries.
In many jurisdictions, synthetic peptides such as those commonly circulating in research supply chains are not approved medicines. They are not authorised for human use outside of specific clinical contexts and are subject to national pharmaceutical and customs regulations. No analytical result on a COA changes this regulatory status. Possession, procurement, or use of these substances without appropriate authorisation may constitute a legal violation in the relevant jurisdiction.
Educational disclaimer: This article is published by Attestory as an educational resource on laboratory document verification. Nothing here constitutes medical advice, clinical guidance, or a recommendation to procure or use any substance. Attestory does not sell products and does not give medical advice. Anyone considering any use of research peptides should consult a licensed physician who can assess their individual situation and the regulatory framework in their jurisdiction.
References: United States Pharmacopeia (USP) general chapters <621> Chromatography and <921> Water Determination; WHO Technical Report Series, Good Practices for Pharmaceutical Quality Control Laboratories; European Medicines Agency (EMA), Guideline on the Specification Limits for Residues of Metal Catalysts or Metal Reagents (EMA/CHMP/SWP/4446/2000); ISO/IEC 17025:2017 General Requirements for the Competence of Testing and Calibration Laboratories. Updated July 2026.