How to Read a Peptide Certificate of Analysis (COA)

A certificate of analysis is a laboratory document that records what a substance is and how pure it is. For a research peptide, a meaningful COA answers two separate questions: is this molecule the one the label claims (identity), and what fraction of the material is the target compound rather than impurities (purity). Everything else printed on a product page, including supplier purity claims and stock photography of vials, is marketing. The COA is the only part that is data, and even then it is only useful if it can be independently verified.

This distinction matters because the research peptide market sits in a regulatory grey zone. The compounds are sold “for research use only” and are not approved for human use, and federal regulators have issued warning letters to multiple online peptide sellers over how those products were marketed. None of that legal context is changed by a COA. A certificate documents chemistry, not legality or safety. For the regulatory picture, see our breakdown of the US legal framework for research peptides.

The bottom line: A certificate of analysis is a chemistry report on identity and purity, and it carries weight only when an independent laboratory issued it and the result can be checked at source.

A complete peptide COA reports two measurements that do different jobs: HPLC measures purity, and mass spectrometry confirms identity. Most independent labs bundle both into a single test result and flag you only if something is wrong, but you should confirm both are present rather than assuming.

HPLC: the purity number

HPLC purity is the percentage of the target peptide relative to all UV-absorbing, peptide-related material in the sample. In plain terms, the lab measures the area of the target peak and divides it by the combined area of every UV-absorbing peak, including truncated fragments, deletion sequences, and synthesis by-products. A reading of 98.7% means the target peptide accounts for 98.7% of the detectable peptide-related material.

The trap is what HPLC cannot see. The figure reflects only UV-absorbing organic impurities. It does not capture water, residual salts, or non-chromophore contaminants, which is why purity and net peptide content are not the same number (covered below). As a rough quality bar, a reading of 99% or higher is excellent and suitable for sensitive work, while 98% is the conventional threshold described as pharmaceutical grade.

Mass spectrometry: the identity check

Mass spectrometry confirms identity by matching the measured molecular weight of the compound against the expected weight for the stated peptide. This is the test HPLC cannot substitute for. A peptide that is missing a single amino acid can read as roughly 99% pure on HPLC and still be 0% the intended molecule, because HPLC measures how clean the sample is, not what the sample actually is. A COA with a high HPLC purity but no mass spectrometry data is incomplete. For a deeper look at how the two methods compare, see our explainer on purity testing methods for peptides.

Test on the COA	What it measures	What it cannot tell you
HPLC	Purity as a percentage of UV-absorbing peptide material	Whether the molecule is the correct one; water, salts, non-chromophore contaminants
Mass spectrometry	Identity, by matching molecular weight to the stated sequence	How pure the sample is
Net peptide content	Actual peptide mass after water, salts, and counterions are removed	Purity profile or identity
Endotoxin (LAL)	Bacterial endotoxin contamination	Identity, purity, or heavy metals
Heavy metals (ICP-MS)	Lead, arsenic, mercury, cadmium and similar	Anything about the peptide itself

The bottom line: HPLC answers “how clean is it” and mass spectrometry answers “is it the right molecule,” and a COA missing either one is only telling half the story.

HPLC purity and net peptide content are different numbers, and a vial can show a high purity figure while containing less actual peptide than the label states. Purity describes how clean the peptide fraction is. Net peptide content describes how much of the vial’s total mass is genuinely peptide once water, residual salts, and counterions such as trifluoroacetate are accounted for. Because HPLC does not measure those non-chromophore components, a 99% pure peptide can still represent only a portion of the powder by weight.

This gap is not theoretical. Independent testing platform Finnrick, which aggregates third-party lab results across the market, found that while average retatrutide purity sat in a tight band of roughly 98.76% to 99.95%, the measured quantity diverged by as much as 50% from the advertised amount at the 95th percentile of samples. In other words, two vials can both report excellent purity while one holds half the peptide the label claims. Purity alone would never reveal that difference.

The bottom line: A high purity percentage does not guarantee the vial holds the labelled quantity, because net peptide content is a separate measurement that purity alone never captures.

A standard HPLC and mass spectrometry COA does not include contaminant screening, and endotoxin and heavy metal tests must be requested separately. The endotoxin test, known as a LAL (limulus amebocyte lysate) assay, checks for bacterial contamination. Heavy metal screening, typically run by inductively coupled plasma mass spectrometry (ICP-MS), checks for elements such as lead, arsenic, mercury, and cadmium.

The absence of these tests on a routine identity-and-purity COA is normal rather than automatically a red flag, because they are separate, optional analyses. Their presence, however, is a stronger quality signal, particularly when sourcing from an unfamiliar supplier. Note that purity, identity, and contamination are independent properties: a compound can be 99% pure and correctly identified yet still carry endotoxin or metal contamination that only a dedicated test would detect.

The bottom line: Endotoxin and heavy metal results are extras that a basic COA will not include, so their presence signals a more thorough supplier rather than their absence signalling a bad one.

A COA is only as trustworthy as the laboratory that produced it, and a seller that tests its own product has a direct financial incentive to report a favourable number. This is why independent third-party testing has become the de facto standard in the research peptide community. The most widely used independent laboratory is Janoshik Analytical, based in the Czech Republic, with others such as BioRegen also named in the space. When a result is issued directly by an independent lab, a stated purity figure means the lab measured that figure, not that the supplier claims it.

Independent labs also publish results to a searchable portal. Janoshik’s verification portal at verify.janoshik.com lets anyone enter a batch reference number and retrieve the lab’s own record of the stated purity and identity. One nuance worth understanding: the lab tests a submitted sample, not every vial in a batch. Batch homogeneity in lyophilised peptide production is generally high, so the result is representative of the batch, but it is best understood as confirmation of the submitted sample rather than a per-vial guarantee.

The bottom line: Independent third-party results that can be checked at the issuing lab carry real weight, while in-house numbers a supplier cannot let you verify carry almost none.

To verify a COA, match the batch or lot number on the vial to the number on the document, then confirm that exact batch in the issuing laboratory’s own records rather than trusting the file the seller handed you. A PDF on its own can be edited; a record held on the lab’s servers cannot. The steps are simple:

• Confirm the compound name on the COA matches what was ordered.
• Check that the batch number on the document matches the number printed on the vial.
• Confirm both HPLC purity and mass spectrometry identity are present, with a date of analysis.
• Enter the batch reference into the issuing lab’s verification portal and confirm the figures match.

The bottom line: Verification is a two-minute check at the issuing lab’s portal, and any certificate that cannot survive that check should be read as a claim, not a result.

What purity figure should a COA show?

A reading of 99% or higher is excellent, and 98% is the conventional pharmaceutical-grade threshold. Below 98%, the proportion of impurities rises and the value of the certificate as a quality signal falls.

Does a COA make a peptide safe or legal to use?

No. A COA documents identity and purity only. It does not confer legal status, regulatory approval, or any assurance of safety for human use, and most research peptides are not approved for human use at all. Whether a vial is clean and correctly identified is a wholly separate question from whether anyone may lawfully use it.

There is no chromatogram on the COA. Is that a problem?

Not necessarily. Some independent labs report numerical purity figures without attaching chromatogram images, which is a presentation choice rather than a sign the result is invalid. As a best practice, you can ask a new tester to provide the chromatogram file so it can be matched against the stated result.

How does a COA fit into choosing a supplier?

A verifiable third-party COA is the single strongest quality signal a supplier can offer, but it is one signal among several. For the wider picture, including enforcement pressure and other warning signs, see our checklist for vetting a peptide supplier.