A Certificate of Analysis (COA) is the most important document associated with any research peptide — more important than the product label, marketing descriptions, or supplier claims. Learning to read and critically evaluate a COA is an essential skill for any UK researcher working with peptide compounds. This guide walks through every section of a COA, explains what the data means, and identifies the warning signs of an inadequate or fraudulent document.
What Is a COA and Why Is It Essential?
A Certificate of Analysis is a technical document generated from analytical testing of a specific batch of a compound. It certifies that the batch has been tested by a qualified laboratory, and provides the actual measured data from that testing. A COA is not a guarantee — it is a record of what testing showed for that specific batch.
For research peptides, the COA serves three critical functions: quality verification (confirming the compound meets the stated purity and identity specifications), batch traceability (linking the document to the specific production lot you received), and research documentation (providing the quality reference data required for valid experimental records and publication).
In peer-reviewed research, authors are expected to report the source and purity of research compounds used. A COA provides the primary documentation for this requirement. Any research institution with an ethics or quality assurance framework will require COA documentation for research compounds.
Section 1: Header Information
The header of a COA should contain the following information, all of which you should verify upon receipt:
Product name and IUPAC/chemical name: Confirms what compound the COA refers to. For peptides, the full amino acid sequence notation should be present (e.g., for BPC-157: Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val).
Catalogue/product number: The supplier’s internal reference for the product — allows cross-referencing with your order.
Lot/Batch number: The unique identifier for the specific production run that was tested. This is the single most important piece of batch traceability information. The batch number on the COA must match the batch number on the vial or packaging you received.
Molecular formula and molecular weight: For peptides, molecular weight is a key identity parameter. The COA should state both the theoretical MW and the MW confirmed by mass spectrometry.
Date of manufacture and expiry date: Relevant for stability assessment and appropriate storage timeline planning.
Testing laboratory name and address: The analytical laboratory that performed the testing. This should be a named, identifiable third-party laboratory — not the supplier itself. If you cannot find this laboratory via an independent search, treat the COA with scepticism.
Section 2: Purity Analysis (HPLC)
Purity by HPLC (High-Performance Liquid Chromatography) is the most fundamental quality parameter for research peptides. Understanding this data requires knowing how HPLC works:
HPLC works by passing the dissolved peptide sample through a column that separates compounds based on their physical and chemical properties (typically hydrophobicity in reverse-phase HPLC). The detector — usually UV absorbance at 220 nm for peptides — measures the concentration of material eluting from the column at each moment in time. The result is a chromatogram: a plot of detector signal against time (retention time).
What to look for in the HPLC section of a COA:
Purity percentage: Expressed as “Area% by HPLC.” This represents the target peptide’s peak area as a proportion of total detected peak areas. A result of 98.5% Area% means 98.5% of the UV-absorbing material in the sample is the target compound, with 1.5% being other compounds (impurities, degradation products). For research use, ≥98% is the standard minimum; ≥99% is preferred for high-sensitivity applications.
Method details: Column type, mobile phase composition, gradient conditions, and detection wavelength should be stated. This allows the analysis to be reproduced independently if verification is required. A COA that states “purity: 98%” without any method detail provides very limited confidence — the result cannot be independently verified.
Chromatogram: Many credible suppliers include the actual HPLC chromatogram in the COA. A high-purity peptide should show one dominant sharp peak with only small satellite peaks. A chromatogram showing multiple significant peaks suggests impurities. If the COA includes a chromatogram, examine it rather than relying solely on the stated percentage.
Retention time: The retention time of the target compound peak should be stated. For identity purposes, this should match the expected retention time for the compound under the stated conditions.
Section 3: Identity Confirmation (Mass Spectrometry)
HPLC purity confirms that the compound is present and reasonably pure, but does not definitively confirm it is the right compound — a contaminant could have a similar retention time. Mass spectrometry (MS) provides the definitive identity confirmation.
Molecular ion (M+H)+: Mass spectrometry measures the mass-to-charge ratio of ionised molecules. For peptides, the most common ionisation method is electrospray ionisation (ESI), which produces multiply-charged ions. The COA should report the measured mass and compare it to the theoretical mass calculated from the peptide sequence.
How to read the MS result: The theoretical molecular weight of the peptide is calculated from its amino acid sequence plus water (MW = sum of amino acid residue weights + 18.02 Da for H₂O). The measured mass in MS should match this theoretical value within instrument tolerance — typically ±0.5 Da for ESI-MS, ±0.005 Da for high-resolution instruments. A mass match to within this tolerance confirms the compound is what it is claimed to be (or has the same molecular weight as the claimed compound — rare exceptions exist for isomeric sequences).
What the MS result cannot tell you: MS confirms molecular weight but not peptide sequence or stereochemistry. It cannot distinguish between a correctly sequenced peptide and one with the same amino acids in a different order (if the MW is the same). For high-confidence identity confirmation, MS/MS (tandem mass spectrometry) with sequence fragmentation is required — but this is not standard in most commercial COAs.
Section 4: Appearance
A simple but important section: the physical description of the product. For lyophilised peptides, this is typically “white to off-white lyophilised powder.” If your received product appears markedly different from the stated appearance (yellowed, wet-looking, crystallised), this is a quality flag worth investigating. Minor colour variation (white to slightly cream) is generally acceptable and within normal variation.
Section 5: Sterility and Endotoxin Testing
Not all COAs include sterility and endotoxin data — these tests are more expensive and are sometimes offered only for injectable-grade products at premium pricing. For any research application involving cell culture or in vivo injection, these parameters are important:
Sterility test: Confirms absence of viable microorganisms (bacteria, fungi, yeast). The compendial test (USP/Ph. Eur.) involves incubating the sample in growth media and observing for growth over 14 days. A negative result (no growth) is reported as “Passes sterility test.” A product failing sterility testing would contaminate cell cultures and potentially cause severe adverse effects in animal models.
Endotoxin test (Bacterial Endotoxin Test/BET): Quantifies bacterial endotoxins (lipopolysaccharides from gram-negative bacteria) using the LAL (Limulus Amebocyte Lysate) assay. Results are expressed in Endotoxin Units per milligram (EU/mg). For general research use, <0.1 EU/mg is a commonly cited threshold. Cell culture is particularly sensitive to endotoxins — even sub-toxic concentrations can activate NFκB signalling in many cell types, profoundly altering gene expression and confounding experimental results. If your COA lacks endotoxin data and your research involves cell culture, request this data or choose a supplier that tests for it.
Section 6: Moisture Content (Karl Fischer)
Lyophilised peptides contain residual water. Moisture content is measured by Karl Fischer titration and expressed as a percentage by weight. This matters because moisture content affects the actual peptide mass you receive per vial:
If a 5 mg vial has 5% moisture content, the actual peptide mass is approximately 4.75 mg — not 5 mg. At modest moisture levels (2-5%), this is a small but real difference that research requiring precise dose-response relationships should account for. High moisture content (>10%) may indicate improper freeze-drying or moisture ingress during storage, which can accelerate peptide degradation.
Red Flags in COA Documents
Beyond the absence of expected sections, specific patterns within present sections should raise concern:
Round-number results: Genuine analytical data rarely produces perfectly round numbers. A COA showing exactly “99.0%” purity, exactly “1000 Da” molecular weight, and exactly “0.1 EU/mg” endotoxins looks suspiciously fabricated. Real analytical data includes decimal precision that reflects actual instrument readout.
Identical COAs across different batches: If you receive COAs for multiple batches that are identical (same data, same date, different batch numbers), this is a serious red flag suggesting fabricated documents.
Missing batch number or batch number mismatch: The batch number on the COA must match the batch number on the product. A COA with no batch number cannot be verified to correspond to any specific production run.
No analytical laboratory identification: A supplier generating their own COA (without a third-party laboratory) has no external accountability for the data presented.
Purity stated by method other than HPLC: Some suppliers state purity by TLC (thin layer chromatography) or simply “by weight” — methods that are far less sensitive and precise than HPLC. Purity should be determined by HPLC for credible research-grade products.
Practical COA Verification Steps
When you receive a new batch of research peptide, follow this verification process before use: check batch number matches between COA and packaging; verify the testing laboratory is named and identifiable; confirm purity meets your minimum threshold (≥98% for most research); check that molecular weight matches the theoretical MW for the peptide; examine the chromatogram if included; confirm sterility and endotoxin data if your application requires it; file the COA with your research records alongside the batch number for documentation purposes.
🔗 Related Reading: For guidance on sourcing quality research peptides in the UK and what to look for in a supplier, see our How to Choose a Research Peptide Supplier UK: What to Look For (2026).
🇬🇧 UK Research Peptides: PeptidesLab UK provides COA documentation with every batch, including third-party HPLC purity, MS identity confirmation, and endotoxin testing. View UK stock →
