For Laboratory & Research Use Only Not for Human or Veterinary Use. This content is intended for qualified researchers and institutions.
A Certificate of Analysis (COA) is the document that tells you what’s actually in the vial not what the label claims, not what the marketing copy promises. If a supplier can’t produce one that names the testing lab, ties results to your specific batch, and reports real numbers instead of vague pass/fail statements, that gap is the whole story. Here’s how to read one properly, section by section.
Guides like Peptidepedia’s COA breakdown make a useful point: most COAs circulating in the research peptide market are technically compliant and practically useless they show a purity number and a lab name, but not enough to catch the failure modes that actually matter. Knowing which fields to check is what separates a COA that passes a checklist from one that actually confirms what you’re holding.
If you haven’t already, it’s worth first understanding why third-party testing matters in the first place this guide assumes that context and walks through the document itself.
What a COA Actually Is
A COA is issued by an analytical laboratory and reports the measured identity, purity, and quality attributes of one specific synthesized batch not the product line in general. A credible COA ties every measurement to a traceable batch or lot number, so the document in front of you should match the vial in your hand, not a “representative sample” tested months earlier.
A COA is not a marketing document, and it doesn’t prove a peptide is safe for any particular use. It’s one part of a broader quality picture the analytical part.
Section 1: Identity Is This the Right Molecule?
The identity section confirms the peptide’s molecular structure, typically via mass spectrometry (MS).
What to check:
- Theoretical vs. observed mass. Every peptide has a calculable theoretical mass based on its amino acid sequence. A credible COA reports both the theoretical mass and the observed (measured) mass and the two should agree closely, typically within a fraction of a Dalton, a benchmark American Peptides’ COA guide also uses when explaining what a high-resolution mass spec analysis looks like on paper.
- Numbers, not just a checkmark. A COA that reports “MS confirmed” with no actual mass figures is documenting nothing reproducible. Look for stated masses, charge states, and ideally the method used (MS or LC-MS).
- Sequence and CAS/molecular formula. The product identification section should list the peptide name, molecular formula, and molecular weight, so you can cross-check it against an independent reference.
Section 2: Purity How Much of the Vial Is Actually the Target Peptide?
Purity is most commonly reported via High-Performance Liquid Chromatography (HPLC).
What to check:
- The percentage itself. Reported as something like “99.4% purity by HPLC.” For quantitative dose-response or publication-grade research, look for 99%+; figures in the 95–98% range may be workable for preliminary screening but introduce more variability, a threshold echoed in Lone Star Peptide Co.’s COA guide, which treats HPLC purity above 98% as one of four non-negotiable checks.
- The chromatogram, not just the number. A complete report includes the actual chromatogram showing the target peak alongside any impurity peaks not just a summary percentage. A single number with no supporting trace is much easier to misstate.
- Both HPLC and MS present. HPLC alone gives you quantity without confirming identity. MS alone confirms identity without quantifying purity. A complete COA has both.
Section 3: What Else Is in the Vial
A lyophilized peptide vial is never 100% pure peptide by mass. Expect to see, or account for:
- Counterions (from TFA or acetate buffers used in purification) often a meaningful share of total vial mass
- Residual water, even after lyophilization
- Residual solvents left over from synthesis
None of this is inherently a problem it’s normal chemistry. The issue is when a COA doesn’t disclose it, leaving you to assume the stated purity percentage means something it doesn’t.
Section 4: Sterility and Contaminant Testing
Beyond identity and purity, a complete panel should cover:
- Sterility — absence of viable microbial contamination
- Endotoxins — quantified via LAL or recombinant Factor C assay, since endotoxins are biologically active even at low concentrations and can confound research results
- Heavy metals — Pb, As, Hg, Cd, typically via ICP-MS
If a COA reports purity and identity but is silent on these, that’s an incomplete picture not necessarily a failed one, but one you can’t fully evaluate.
Section 5: Batch Traceability
The single most important administrative detail on a COA is the lot or batch number, and it should match what’s printed on the vial you actually received. A COA with no batch number, or one that’s reused across many production runs, isn’t telling you anything about the specific product in front of you.
Red Flags to Watch For
- No named testing laboratory just “independent lab” with no identifying details
- No batch number, or a batch number that doesn’t match your vial
- A purity percentage with no chromatogram or supporting data
- “MS confirmed” with no actual mass figures reported
- A COA dated long before your order, suggesting it’s a generic document rather than batch-specific testing
How This Connects to Third-Party Testing
Reading a COA correctly only matters if the COA itself came from an independent lab in the first place. A perfectly formatted COA from an in-house lab is still a self-graded result. For the full picture of why that distinction matters and how to verify a lab’s accreditation see Why Third-Party Testing Matters for Research Peptides.
Frequently Asked Questions
What’s the minimum a peptide COA should include?
At minimum: a named testing lab, a batch/lot number matching your vial, HPLC purity with a chromatogram, and mass spectrometry identity confirmation with actual mass figures not just a pass/fail statement.
Is 95% purity good enough?
It depends on the use. Preliminary screening work may tolerate 95–98% purity, but quantitative dose-response or publication-grade research generally calls for 99%+.
Why does a COA need to show both HPLC and mass spec results?
HPLC quantifies purity but doesn’t confirm identity. Mass spectrometry confirms identity but doesn’t quantify purity. Both are needed for a complete quality picture.
What does it mean if a COA has no chromatogram?
It means you’re trusting a summary number with no supporting evidence behind it. A complete report includes the actual chromatogram, not just the final percentage.
Compliance note: This content is intended for qualified researchers and institutions. Products referenced are sold strictly for laboratory and research use only and are not drugs, foods, cosmetics, or dietary supplements. They are not approved by the FDA and are not intended to diagnose, treat, cure, or prevent any disease, and are not for human or veterinary consumption.