5 July 2026 · 10 min read
How to Read a Peptide Certificate of Analysis (COA)
When you work with peptide reference materials, the Certificate of Analysis is the document that ties a specific batch to the data you are using to justify quality.
It tells you what was tested, how it was tested, and what the results were. If you can read a COA quickly and confidently, you can decide whether a batch is suitable for your research protocol or whether documentation is too limited to support your experiments.
What a COA is
A COA is a batch-level analytical report issued by a testing laboratory.
Following a defined set of tests, the lab records the results for:
- Identity (is this the peptide you think it is?)
- Purity (how much of the material is the target compound?)
- Other quality parameters (appearance, water content, residual solvents)
A strong COA is written in technical language and includes methods, numbers and reference data. It is not marketing copy. It is a document you can file, audit and refer back to when you write up results or respond to questions from reviewers.
Section 1: header and batch identity
Begin at the top of the document. You are checking that you are looking at the correct COA for the correct vial.
You should see:
Product name and identifiers
Exact peptide name, often with sequence and molecular formula. This is your first confirmation that the document refers to the compound you believe you are handling.
Batch / lot number
Every useful COA is tied to a specific batch. The batch or lot number on the COA should match the batch or lot number on your vial or label. If these do not match, the COA does not apply to that vial.
Testing laboratory details
A named lab with contact information, ideally accredited for this type of testing. If you cannot identify the lab from what is printed on the COA, that is a concern.
Test date (and sometimes manufacturing / expiry date)
You want analytical data that is reasonably recent for the stock you are currently holding. A very old test date for material presented as current inventory is a warning sign.
If the header is vague, missing a batch number, or the lab looks difficult to verify, you should treat the document as insufficient for serious research use.
Section 2: purity (HPLC)
For peptides, High-Performance Liquid Chromatography (HPLC) is the standard method used to express purity.
On the COA, focus on three things:
Purity percentage
Often reported as “HPLC purity” or equivalent. Many guides and laboratories treat ≥98% as a sensible lower bound for research-grade materials, with ≥99% preferred for more demanding applications.
Chromatogram
The chromatogram shows the analytical trace. You want a single dominant peak corresponding to the target peptide, with only minor secondary peaks. Purity percentage is calculated as the area of the main peak divided by total peak area.
Method summary
Information such as column type, mobile phase, gradient, and detection wavelength. You do not need to replicate the method, but its presence indicates that the test was properly documented.
Red flags
- “High purity” with no numeric result
- Purity percentage with no chromatogram
- Multiple large peaks of similar height
- Purity well below your minimum threshold with no explanation
Section 3: identity (mass spectrometry)
Purity tells you how clean the sample is. Mass spectrometry tells you what the molecule is.
Look for:
Theoretical molecular weight
Calculated from the peptide sequence. This is the value the molecule should have if synthesised correctly.
Observed molecular weight
Measured by the mass spectrometer.
Match tolerance
The observed value should be very close to the theoretical value, typically within standard instrument tolerance (often around 0.1% or within ±1 Da for many peptides). Larger differences require explanation.
A COA with only purity data and no mass spectrometry section is not providing full identity confirmation.
Section 4: other quality parameters
Depending on the application and the lab, you may also see:
Appearance
Usually “white to off-white lyophilised powder”. Significant deviations can indicate degradation or contamination.
Water / moisture content
Relevant if you are performing precise mass-based calculations.
Residual solvents
Panels for common synthesis solvents (eg TFA, acetonitrile, DMF). The presence of this data is a positive quality indicator.
Endotoxin / microbial testing
Reported in appropriate units when performed. Especially relevant for certain experimental contexts.
Missing data in these areas does not automatically disqualify a batch for research use, but it does limit how confidently you can claim quality in your records.
Section 5: a practical verification workflow
When you receive a new batch of peptide reference material, use a simple, repeatable check:
Match the batch number
Confirm that the batch or lot number on the COA exactly matches the one on your vial or label.
Confirm the lab and date
Verify that the testing laboratory is clearly named and identifiable, and that the test date is recent enough to be relevant to current stock.
Check purity and chromatogram
Ensure HPLC purity meets your minimum threshold and that the chromatogram shows a dominant main peak with acceptable minor peaks.
Verify identity via mass spectrometry
Confirm that theoretical and observed molecular weights are reported and closely matched within tolerance.
Review additional metrics relevant to your work
For example, water content, residual solvents, or endotoxin results. Record anything that could affect your experimental design.
File the COA with your records
Store a digital copy in your laboratory documentation system, linked to the batch number, supplier and project or protocol IDs. This will support reproducibility and audit readiness.
If any element looks wrong or incomplete, query it before use. Reputable suppliers will be comfortable explaining their documentation and, where necessary, providing updated or batch-specific COAs.
Section 6: common red flags
Some patterns are consistently cited in guides on weak or unreliable COAs.
Be cautious if you see:
- No batch or lot number
- Generic COAs that apply to “all batches” rather than a specific one
- No named testing laboratory; only in-house or anonymous testing
- Purity data with no chromatograms or method details
- Identity claims with no molecular weight data
- Very old test dates for new batches
One issue on its own may be an oversight. Multiple issues together suggest the product is insufficiently documented for serious research.
Section 7: research use only and regulatory context
Finally, a note on regulatory boundaries.
In the UK, peptides supplied as research-use-only laboratory reagents are treated differently from medicinal products regulated by the MHRA. How they are presented and discussed is part of what determines how they are classified.
This guide is written for researchers handling peptide materials as laboratory reagents, not as medicines or for personal administration. Nothing here is medical advice, and nothing on Edinburgh Peptides should be interpreted as a recommendation for human or veterinary use. Keeping that boundary clear in your copy, product pages and documentation is essential to staying on the right side of UK rules on unlicensed and prescription-only medicines.