What is a Peptide Certificate of Analysis (COA)?
Quality verification
What is a peptide COA, and how to read one.
A Certificate of Analysis is the document that verifies what you actually received. For research peptides, the COA tells you the compound’s identity, its purity, its contamination profile, and the batch lot. Here is what each section means and how to read it like a researcher.
Quick answer
A peptide COA documents three things: identity (mass spectrometry confirms the molecule is what the label says), purity (HPLC measures how much of the sample is the target compound), and contamination (LAL endotoxin testing confirms the batch is free of bacterial contamination). Without a published COA tied to your batch lot, you have no verification.
What a COA actually verifies
A Certificate of Analysis is a third-party-generated document that tests a specific batch of compound and reports the results against published specifications. The three core tests for a research peptide COA are mass spectrometry (identity), high-performance liquid chromatography (purity), and LAL endotoxin screening (bacterial contamination).
Each COA is tied to a specific batch lot number. The batch lot on your physical vial should match the batch lot on the COA you reference. If they don’t match, the COA is not verifying your specific material.
A COA published by the supplier itself is less independent than a COA generated by an outside laboratory. Reputable peptide suppliers use independent third-party labs for COA generation, document the lab and the test dates, and publish the results without modification.
Identity verification: mass spectrometry
Mass spectrometry measures the molecular weight of the compound in the sample. The measured mass is compared against the theoretical mass of the labeled peptide sequence. A match within standard tolerance (typically ±2 daltons for peptides in this mass range) confirms the identity.
Common identity verification methods include MALDI-TOF (matrix-assisted laser desorption/ionization, time-of-flight) and ESI-MS (electrospray ionization mass spectrometry). Both are appropriate for peptide identity verification at the precision required for research.
If the measured mass differs significantly from the theoretical mass, the sample contains a different compound than labeled. This is the most fundamental quality check on a peptide batch.
Purity verification: HPLC
High-performance liquid chromatography (HPLC) separates the components of a sample based on their interaction with a stationary phase. For peptide purity verification, reverse-phase HPLC is the standard method.
The HPLC chromatogram shows peaks for each component in the sample. The area under each peak is proportional to the amount of that component. Purity is calculated as the area of the target peptide peak divided by the total area of all peaks, expressed as a percentage.
Research-grade peptide purity standards are typically 95-99%+ depending on the application. Aeternum Labs verifies every batch to 99%+ HPLC purity, which means the vast majority of the material in the vial is the target compound with minimal impurities or related sequences.
Lower purity grades exist for specific applications but should be avoided for research where the impurity profile could confound endpoint measurements. The 1% or less of non-target material in a 99%+ purity sample is usually closely-related sequence variants rather than unrelated contaminants.
Contamination screening: LAL endotoxin testing
Endotoxins are lipopolysaccharides released from the cell walls of gram-negative bacteria. They can produce inflammatory responses in research models even at picogram-per-milliliter concentrations. Endotoxin contamination is a major confounding variable in peptide research, particularly for compounds being studied for immune or inflammatory endpoints.
The Limulus amebocyte lysate (LAL) assay detects endotoxin contamination based on the clotting response of horseshoe crab amebocyte lysate to bacterial lipopolysaccharide. The assay is highly sensitive, capable of detecting endotoxin at the 0.005 endotoxin unit per milliliter level.
A research-grade peptide COA should report LAL endotoxin testing with results below the relevant threshold for the intended application. For most research peptide applications, levels below 1 EU/mg are acceptable; levels below 0.1 EU/mg represent ultra-low endotoxin material suitable for sensitive immunological research.
How to verify a COA before ordering
A reputable peptide supplier publishes COAs publicly so prospective customers can verify quality before placing an order. Aeternum Labs publishes every batch COA in the public COA library at /coa-library/, with each entry tied to a specific batch lot number.
When evaluating a supplier, look for: third-party lab name and accreditation, test dates that match the batch production date, results presented as actual data (chromatograms, mass spectra) rather than just summary statements, and the ability to look up your specific batch lot after receiving the product.
Suppliers who claim ‘COA available upon request’ but don’t publish them publicly are not providing the same level of transparency as suppliers who publish all COAs in a public library. The lack of public verification means you cannot evaluate quality before ordering.
What's missing from most COAs (and why)
Most commercial peptide COAs report identity, purity, and endotoxin. Some advanced testing is available but rarely included in standard COAs due to cost: amino acid analysis (verifying exact sequence composition), sequence confirmation by tandem mass spectrometry (verifying the order of amino acids, not just the mass), residual solvent testing (detecting synthesis-residual chemicals), and bioactivity assays (confirming the peptide retains biological function).
For most research applications, the standard identity-purity-endotoxin trio is sufficient. Specialized applications (clinical research, regulatory submissions, comparative bioactivity studies) may require expanded testing. Aeternum Labs can arrange expanded testing on request for laboratories with specific protocol requirements.
Frequently asked questions
What does a COA prove that a label doesn't?
The label states what the supplier intended to put in the vial. The COA is independent verification that the contents match the label, generated by laboratory testing of the actual material. Labels can be wrong (mis-labeling, supplier error). COAs can be wrong only if the testing lab itself fabricates data, which is detectable through pattern analysis across batches.
Why does HPLC purity matter so much?
HPLC purity tells you what percentage of the material in the vial is actually the target compound. A 90% pure peptide vial contains 10% of something else, which could be a different sequence variant, a synthesis byproduct, or a degradation product. For quantitative research, you need to know the actual concentration of the active compound, which requires high purity. 99%+ purity makes the dose math reliable.
What does an endotoxin test tell me?
It quantifies bacterial lipopolysaccharide contamination in the peptide sample. Endotoxin can produce inflammatory responses in research models even at trace concentrations, which can confound immune or inflammatory research endpoints. Low endotoxin (below 1 EU/mg) is suitable for most applications; ultra-low (below 0.1 EU/mg) is required for sensitive immunological research.
Should I trust a supplier who says COAs are 'available on request'?
Be cautious. Public COA libraries demonstrate that the supplier is willing to be evaluated before purchase. ‘Available on request’ could mean COAs exist but are deliberately hidden, or it could mean they don’t actually exist and would be generated only if asked. Public COAs are a stronger transparency signal.
How do I match my batch to its COA?
The batch lot number on your physical vial should match the batch lot on the COA. Look for the lot number printed or stickered on the vial; cross-reference it against the COA library entry for that lot. If the COA library doesn’t list your specific lot, contact the supplier — they should be able to provide the matching COA immediately.
References
- United States Pharmacopeial Convention (2020). USP <85> Bacterial Endotoxins Test. View source
- Hooper J (2010). Peptide synthesis quality control and characterization. View source
Reviewed by
The Aeternum Labs Research Team
Compounds, COAs, and protocol design
The Aeternum Labs research team verifies every batch in our library against published purity and identity standards. Master guides summarize publicly available scientific literature and pharmaceutical-handling best practices.
Research Disclaimer. All compounds discussed in this article are sold by Aeternum Labs for in vitro laboratory research purposes only. They are not intended for human or animal consumption, diagnosis, treatment, or prevention of any disease or condition. Information presented is summarized from publicly available scientific literature and should not be construed as medical advice.