Peptide COA guide: verify identity, amount and purity
Match a peptide COA to its lot, verify it with the issuing laboratory, and distinguish measured content from chromatographic purity and other tests.
In this article
A certificate of analysis reports results for a submitted sample under specified methods. Start by connecting that sample to the product and lot you are assessing. A readable, authentic report is useful evidence; it does not establish that every container was sampled or that the lot currently being sold is the one in the report.
Match the sample, product and lot
- Record the laboratory name, report or task number, sample identifier and report date.
- Compare the compound name, formulation, labeled amount and lot identifier with the supplier’s product record and package label.
- For a blend, check every named component and stated ratio rather than only the combined amount.
- Ask the supplier to explain missing identifiers, inconsistent names or a report that cannot be tied to the lot offered.
Identity, amount and purity are different results
Identity testing addresses what was detected. A quantitative assay reports an amount or concentration with units. Chromatographic purity is a result under the stated separation and detection method; a peak-area percentage should not be read as a direct measurement of milligrams in a vial. Methods and the treatment of impurities matter: NIST’s peptide measurement research examines multiple approaches to assigning purity mass fraction.
NIST: methods for assigning peptide purity mass fraction
For an illustrative example, a report might identify a sample labeled 10 mg, report 9.6 mg measured content, and show 99.2% chromatographic purity. Those are different fields, not competing versions of the same number. This is a fictional example to explain the distinction, not a test result for a listed vendor.
Look for the analytical scope you need
Do not read a purity result as proof of every possible property. Janoshik lists peptide analysis separately from endotoxin, sterility and contaminant screening services. Check which tests actually appear on the report; a percentage or a pass label is not a general safety certification.
Janoshik: published testing services and scope
Verify the original with the issuing laboratory
Use the laboratory’s official website rather than relying only on a seller-hosted image. Janoshik’s verification page, for example, asks for a task number and unique key. Compare the returned laboratory record with the supplied document. A verification result authenticates that report; matching it to the supplied material remains a separate check.
Janoshik: official report verification
Download the printable peptide COA checklist
When to request more evidence
- A cropped or unreadable report hides identifiers or analytical details.
- The report is for another compound, formulation, amount or lot.
- The seller quotes a purity number but does not provide the requested assay amount or test scope.
- A historical result is presented as proof of the lot shipping now.
- The verification link does not lead to the issuing laboratory, or the laboratory record differs from the supplied copy.
Use the directory and archive with their stated limits
A link to a vendor’s COA library is a route to the evidence, not a PeptideTech certification of its inventory. Historical reports in our archive remain historical and do not certify the vendors in today’s price comparison. Assess the original report and the current lot together.
Search the historical COA library
Correction and sources
The original article described a COA as the one document proving what is in a vial and made blanket vendor-testing assertions. This revision separates report authenticity, sample identity, measured amount, analytical scope and the connection to a current lot.
Editorial revision: 17 September 2026. The original publication date is preserved. Offer observation dates, laboratory report dates and coupon checks are separate from this editorial date.
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