How to read a peptide certificate of analysis (COA)

Prepared by: Research Desk. Sources are linked for verification.

Published 19 October 2026

A certificate of analysis (COA) is a laboratory's report on a sample of material. For synthetic peptides sold for laboratory research, the COA is usually the only quality document a buyer sees. This guide explains what the common fields mean, which warning signs to look for, and what a COA cannot show. It describes documents only and says nothing about the uses or effects of any compound.

To check a specific report field by field, use the free COA field checker.

The fields on a typical COA

HPLC purity

High-performance liquid chromatography (HPLC) separates the components of a sample as they pass through a column. For peptides this usually means a column with a non-polar stationary phase and ultraviolet detection, and the chromatogram shows each component as a peak. The purity figure is normally the area of the main peak as a percentage of the total peak area.

Two points matter when reading that number:

It is a relative figure. Area percent compares the peaks the detector can see. Water, salts and counter-ions such as trifluoroacetate, which is left over from purification, do not show up the same way. A sample reported as 99% pure by HPLC is not 99% peptide by weight. The share of peptide by weight is called the net peptide content and needs a separate test, such as amino acid analysis.
It depends on the method. Closely related impurities can elute together with the main peak and be counted as part of it. A review of related impurities in peptide medicines describes the main types: deletion and insertion sequences, incomplete deprotection, oxidation, deamidation and diastereomers (D'Hondt et al., 2014, PubMed). A useful COA states the column, the gradient and the detection wavelength, and attaches the chromatogram itself rather than only the final figure.

MS identity

Mass spectrometry (MS) measures the mass of the molecules in the sample. On a COA it answers a different question from HPLC: is the main component the compound named on the label? A good report shows the expected molecular mass next to the observed mass. MS does not measure purity, and it cannot tell apart forms with identical mass, such as some diastereomers. HPLC and MS are complementary, so a COA with only one of them leaves a gap.

Batch or lot number

A batch, or lot, is a specific quantity of material made in one process run and expected to be uniform within set limits. This is the definition used in the ICH good manufacturing practice guideline for active ingredients (ICH Q7, listed on the ICH quality guidelines page). The batch number is what links a report to a physical container. If the number on the report does not match the number on the label, the report describes some other material.

Testing laboratory

The report should name the laboratory that ran the test, with enough detail to contact it. Some laboratories are accredited to ISO/IEC 17025, the international standard for the competence of testing and calibration laboratories. Accreditation bodies use it to assess laboratories. Accreditation covers a defined scope of tests, so the method on the report should fall within that scope. Most accreditation bodies publish a searchable register.

Dates

A COA should show when the sample was tested. Compare that date with the batch number and with the date the material was made. A test date that comes before the batch could have existed, or a single report reused for years of production, is worth questioning.

Client and manufacturer

Many reports name the client that sent the sample. If the client named is a different company from the supplier, the report may be genuine but describe material from another source. Ask the laboratory who requested the test.

Verification

Some laboratories offer a verification page where a report ID can be entered, or confirm reports by email. Find the laboratory's contact details independently, for example from its own website, rather than from a link or QR code printed on the report, since those can be copied along with the rest of the document. Ask the laboratory to confirm the report ID, the compound, the batch and the results.

Red flags

No laboratory named, or a laboratory that cannot be found independently.
A report ID that the laboratory cannot confirm.
The same batch number on reports for different compounds.
A purity figure with no method, no chromatogram and no MS data.
A client or manufacturer name that does not match the supplier, with no explanation.
Dates that do not fit together, or a report that looks edited, such as mismatched fonts or a missing signature block.
A supplier statement that every batch has a report, when reports are published for only some products.

Analytical work on seized falsified peptide products has found impurity profiles that the paperwork did not reveal (Janvier et al., 2018, PubMed). A clean-looking document is not the same as a confirmed result.

What a COA does not prove

It describes the sample tested. A COA reports on the portion of material the laboratory received. It shows something about other containers only if they come from the same batch and the batch is uniform.
It covers only the tests listed. If a report shows HPLC and MS only, it says nothing about water content, counter-ion content, endotoxin, sterility or heavy metals.
It depends on the method. Whether a method can actually separate and detect the relevant impurities is a matter of validation. The ICH Q2(R2) guideline on validating analytical procedures, also listed on the ICH quality guidelines page, sets out what that involves, including specificity, accuracy and precision.
It is not a statement about use. A COA is an analytical record. It does not show that a material is suitable for any purpose, and it is not evidence of safety.

A short checklist

Is the laboratory named, and can it be contacted independently?
Does the laboratory confirm the report ID?
Does the batch number match the container label?
Are both HPLC (with a chromatogram) and MS identity shown?
Do the dates and the client name fit the material in hand?

The COA field checker runs through these questions in the browser. How listings on this site are checked is described on the methodology page.

Where this guide fits

This site lists one research supplier, Purita, which publishes COA files for some of its products on its certificates page.

Visit the Purita website

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