How to Read a Peptide Certificate of Analysis (CoA)

Last updated October 8, 2026

A peptide CoA (Certificate of Analysis) is the laboratory record that ties one batch of a research peptide to the tests that were run on it. This guide explains how to read a peptide Certificate of Analysis field by field, how to verify it on the testing laboratory’s own platform, which signs point to a weak document and what a CoA cannot tell you, with a real batch record from our archive as the worked example.

What is a peptide CoA?

A Certificate of Analysis is issued by a testing laboratory for one specific batch (also called a lot) of material. It records which tests were run on a sample of that batch, by which method, on which date and with what result. It is evidence about that batch only: a report for a different lot says nothing about the vial in front of you, even when the compound name is the same.

For research peptides, the CoA is often the only independent evidence a buyer can check before ordering. That is why three things matter as much as the numbers on it: who issued it, whether it can be opened at source, and whether its batch number matches the label on the vial.

Which fields should a peptide Certificate of Analysis contain?

A useful report states, at a minimum:

Compound name: must match the compound on the vial label.
Batch or lot number: must match the lot printed on the vial. This is the field that connects the document to the material.
Test date: when the sample was analysed or the report was issued. An undated report cannot be placed in a batch history.
Method: purity is usually measured by HPLC (high-performance liquid chromatography); identity is usually confirmed by mass spectrometry (MS).
Result: the measured value for that batch, not a range or a marketing figure.
Laboratory: the independent laboratory that performed the analysis.
Verification link or code: a way to open the same report on the laboratory’s own platform.

Purity in percent versus content in milligrams

Purity and content are different measurements. A purity figure such as 99.6% describes what share of the material detected by the method is the target peptide. A content figure in milligrams describes how much of the compound was measured in the sample. Some compounds are reported one way, some the other: in our archive, the report for NAD+ lot GY058 gives a content of 509.15 mg rather than a percentage. Read the unit before comparing two reports, and never treat a figure in mg as a purity claim.

Identity is a different test from purity

HPLC purity shows how clean a sample is, not what it is. A sample can be very pure and still be the wrong peptide. Identity testing, usually by mass spectrometry, confirms that the main component has the molecular mass expected for the sequence. If a report lists purity only, identity has not been confirmed for that batch.

Endotoxin and heavy metals

Bacterial endotoxin (usually measured with the LAL method) and heavy metals (an elemental-impurities screen, often by ICP-MS) are separate assays. They appear on a CoA only if they were run on that batch. A report that does not list them has not tested them, and the results of another lot cannot fill the gap.

How do you verify a peptide CoA at source?

Find the batch number printed on the vial label.
Open the matching record, for example from the lab reports archive, where each batch links to the laboratory’s own report.
Check that the link opens on the testing laboratory’s own website, not on the seller’s.
Compare the compound, batch number, test date and result on the laboratory’s page with the copy the seller shows.
Check which tests were run on that batch. Not every batch has been through every test.
If anything does not match, contact the supplier before using the material in research.

A screenshot or a PDF hosted by the seller is a copy. The record held by the laboratory is the original; if the two disagree, the laboratory’s version is the one that counts.

What are the red flags on a Certificate of Analysis?

The same report, with the same verification link or the same result, presented for different products or for different lots.
Only a screenshot or a supplier-hosted PDF, with no way to open the report on the laboratory’s platform.
No batch number, no test date, or a batch number that does not appear in the supplier’s own archive.
A purity claim for a product with no matching report for the lot actually on sale.
A “typical” or “representative” CoA instead of a report for a named batch.
Tests mentioned in the product description that do not appear on any report.

A real example: reading lot XD-RT10-PO06

This is how the fields read on one record from our archive, retatrutide lot XD-RT10-PO06:

Compound: retatrutide.
Batch: XD-RT10-PO06.
Test date: 1 October 2026.
Tests listed: purity, identity, bacterial endotoxin and heavy metals.
Result: purity 99.6%.
Verification: the report opens on the issuing laboratory’s own platform: open the report at source.

The same archive also holds an earlier retatrutide lot, GY035, tested on 20 March 2026 for purity only (99.7%). That report confirms nothing about identity, endotoxin or heavy metals, and the results of lot XD-RT10-PO06 do not carry back to it. That is the habit worth keeping: read every result against its own batch number.

How to compare two peptide CoAs

When two suppliers, or two lots from the same supplier, show different figures, compare like with like: the same compound, the same unit (percent or mg), the same method and a test date for each. A higher purity figure measured by a different method, or on an older lot, is not a better result for the vial you would receive. A report that lists more tests is more informative only for the batch it names.

What does a Certificate of Analysis not tell you?

A CoA describes a sample of one batch on the day it was tested. It does not cover how the vial was stored or shipped afterwards, and it says nothing about any test that is not listed on it. Purity testing is not identity confirmation unless an identity assay was run on that batch.

A Certificate of Analysis is also not a statement of safety or of suitability for use in humans or animals. Peptra Labs materials are supplied strictly for in-vitro laboratory research, and a good CoA does not change that boundary.

Why a supplier should keep earlier batch records

A supplier sells several lots of the same compound over time, and a vial bought months ago may come from an earlier one. An archive that keeps every published batch, not only the newest, lets you match any vial to its own record, see which tests each lot went through, and notice when a newer lot was tested more broadly than an older one, as with the two retatrutide lots above.

Where to find our batch records

Every published batch record, with its test date, the tests that were run and a link to the laboratory’s own report, is listed in our peptide Certificate of Analysis archive. Type the batch number from your vial into the lookup at the top of the archive to open its record.