How to read a peptide COA: step-by-step guide

The Certificate of Analysis is the only objective evidence that a peptide is what it claims to be. Without it, everything else — the branding, the website, the vial photos — is marketing. Knowing how to read a COA is the single skill that best protects an informed buyer, and it is the first step of the verification standard. This guide explains, in plain language, what a laboratory actually examines when it interprets a COA.

What a COA is and what it proves

A COA is a report issued by an analytical laboratory after examining a representative sample from a batch. It answers two distinct questions: is this the correct molecule? (identity) and what proportion of the sample is that molecule? (purity). A serious certificate goes beyond a stamp: it shows the methods used, the numerical results, and — in the best cases — the chromatograms that underpin those figures.

It is equally important to understand what a COA does not guarantee. It does not confirm that the vial you receive at home is identical to the sample analysed, it does not certify sterility or fitness for human use, and it does not under any circumstances replace the assessment of a licensed healthcare professional. It is one piece of evidence about the quality of a batch, not a permit to use it.

Fields that every serious certificate must show

Before looking at the purity figure, check that the basic fields are present. If any are missing, the certificate loses its evidential value:

• Compound name and chemical reference. The declared peptide, ideally with its CAS number and molecular formula.
• Batch number and date. Must match the physical batch you will receive, not a generic code displayed on the website.
• Analytical methods. At minimum, HPLC for purity and, in complete certificates, LC-MS for identity.
• Results with acceptance criteria. The purity percentage and detected mass, alongside the threshold the batch must clear.
• Issuing laboratory. Name, identification details, and ideally an independent way to verify the certificate externally.

An annotated COA example, field by field

This is what a well-constructed certificate looks like. The example below is a purely illustrative document for educational purposes — it does not correspond to any real product, brand, or batch. The numbered markers show what to look at and why.

1. 1
   Compound name and chemical reference.

   The declared peptide with its CAS number and molecular formula. Warning: no CAS or formula means no traceability.
2. 2
   Batch number.

   Must match exactly the batch of the product in your hands. Warning: a generic or mismatched batch number invalidates the certificate.
3. 3
   Identity by LC-MS.

   The detected mass must match the theoretical molecular weight (retatrutide ≈ 4731.33 g/mol). Warning: if the mass does not match, what is inside is not what is declared.
4. 4
   Purity by HPLC.

   What proportion is the peptide versus impurities; the standard is ≥98%. Warning: below 98%, or without a stated method, is a red flag.
5. 5
   Chromatogram.

   The graph that underpins the purity figure: one clean, dominant main peak. Warning: a high percentage without a chromatogram, or with several large peaks, does not hold up.
6. 6
   Independent laboratory.

   Issued by an identifiable third party — not by the seller. Warning: an in-house PDF is not verification.
7. 7
   Date and internal consistency.

   Date of analysis, signature, and results with no internal contradictions. Warning: no date or contradictory data means discard.

Identity: what LC-MS actually measures

Liquid chromatography–mass spectrometry (LC-MS) measures the molecular mass of what is present in the sample. Its role is identity confirmation: the detected mass must match, within a very narrow margin, the theoretical molecular weight of the declared peptide. It is the test that distinguishes, for instance, a genuine retatrutide from a different peptide sold under the same label — a problem that has become especially common in 2026 given how frequently retatrutide is counterfeited.

Reference molecular weights (theoretical data)

Peptide	CAS	Formula	Mol. weight
Semaglutide	910463-68-2	C₁₈₇H₂₉₁N₄₅O₅₉	4113.58 g/mol
Tirzepatide	2023788-19-2	C₂₂₅H₃₄₈N₄₈O₆₈	4813.45 g/mol
Retatrutide	2381089-83-2	C₂₂₁H₃₄₂N₄₆O₆₈	4731.33 g/mol

If a COA declares "retatrutide" but the LC-MS mass does not approach 4731.33 g/mol, there is a contradiction that invalidates the certificate outright. That check — comparing two numbers — eliminates a substantial share of counterfeits at a glance.

Purity: how to read the HPLC result

High-performance liquid chromatography (HPLC) separates the components of a sample and measures how much of the total each one represents. The key figure is the purity percentage: what proportion of the sample is the target peptide compared to all impurities combined. The widely accepted quality benchmark for research peptides is ≥98%.

In the chromatogram, the peptide appears as a tall, well-defined main peak. The smaller peaks around it are impurities: synthesis fragments, by-products, or salts. Things worth paying attention to:

• One clean, dominant main peak signals good purity; multiple large secondary peaks suggest the opposite.
• The declared percentage must be consistent with the graph. A "99.5%" figure alongside a chromatogram with prominent secondary peaks does not add up.
• Be sceptical of round numbers without a chromatogram. An isolated figure, unsupported by the graph that should underpin it, is straightforward to fabricate.

How to interpret HPLC purity

Purity (HPLC)	Reading
≥ 99%	Excellent. Expected from a well-synthesised and purified batch.
98–99%	Accepted quality standard for research peptides.
95–98%	Below the usual threshold. Ask for an explanation of the impurity profile.
< 95% or no figure	Red flag. Insufficient quality or incomplete certificate.

How to detect a fake or altered COA

The certificate itself can be the counterfeit. These are the patterns that expose an unreliable COA:

1. No batch number, or a batch that does not match the product you received. The COA must be for that exact batch.
2. Issued by the seller themselves rather than an independent laboratory. An in-house PDF is not verification.
3. No methods or chromatograms — just a large percentage figure and a logo. The evidence is in the graph, not the decoration.
4. Internal inconsistencies: the LC-MS mass does not match the compound, or the purity figure does not match the chromatogram.
5. Impossible to verify: there is no way to cross-check the certificate against the laboratory that supposedly issued it.

Checklist: read any COA in five steps

1. Batch. Does the certificate batch number match the product? If not, stop here.
2. Identity. Does the LC-MS mass match the molecular weight of the declared peptide?
3. Purity. Does the HPLC show ≥98% and does the chromatogram back it up with a clean main peak?
4. Laboratory. Is it independent, identifiable, and externally verifiable?
5. Consistency. Are there a date, methods, and results with no internal contradictions?

If all five points are green, you have a reliable certificate. But remember that a clean COA certifies the quality of the batch — not the safety of its use. That decision always belongs to a licensed healthcare professional. That is why the next step of the verification standard is understanding why these compounds are used under medical supervision.