A practical guide to the numbers on a peptide certificate, what they mean, and how to tell a real COA from a decorative one.

If you buy research peptides, the Certificate of Analysis is the single most important document you will read. It is the difference between “we say it is pure” and “here is the independent test that shows what is in the vial.” Yet most COAs go unread, partly because the layout is intimidating and partly because no one explains what the fields actually mean.

This guide walks through a peptide COA line by line, in plain language, so you can evaluate any certificate with confidence.

What a Certificate of Analysis is

A Certificate of Analysis (COA) is a document produced by a testing laboratory that reports the measured properties of a specific lot of material. The key phrase is specific lot. A COA is not a general statement about a product. It describes the exact batch that was tested, identified by a lot or batch number. Two vials of the same compound from different lots can, and often do, have slightly different results.

A useful COA answers three questions: What is it? How much of it is there? What else is in it?

The header block: identity and traceability

Before any test results, a real COA establishes what was tested and when. Look for:

Product or compound name. The material the lab believes it received.
Lot / batch number. The unique identifier that ties this certificate to a physical batch. If a COA has no lot number, it cannot be verified against anything.
Analysis date and received date. When the lab tested the sample.
Testing laboratory. The name and, ideally, the accreditation of the lab that ran the analysis.

If a certificate is missing the lot number or the testing lab, treat it as marketing, not documentation.

Identity testing: is it actually the compound?

Identity confirms the sample is the molecule it claims to be, not a look-alike or a mislabel. On a peptide COA you will usually see identity confirmed by one or both of:

Mass Spectrometry (MS). Measures the molecular weight of the peptide and compares it to the theoretical weight. A match within a small tolerance confirms identity.
HPLC retention time. Compares how the sample moves through a chromatography column against a known reference.

The result you want is a clear “confirmed” or a measured mass that matches the compound’s known molecular weight.

Purity: how much of the sample is the target compound

Purity is the number most people look for, and it is usually measured by HPLC (High-Performance Liquid Chromatography). HPLC separates the components of a sample and reports each as a percentage of the total.

A purity figure of, for example, 98% means that 98% of the detectable material is the target peptide and the remaining 2% is other peptide-related species. A few things worth understanding:

Purity is method-dependent. The same sample can read slightly differently on different HPLC methods. A serious COA states the method and wavelength used.
Purity is not the same as content. A sample can be highly pure and still contain less peptide than labeled, because lyophilized powder includes water and counter-ions. That is why the next field matters.

Net peptide content: how much peptide is really in the vial

Net peptide content (sometimes “peptide content” or “assay”) reports how much of the vial’s weight is actually peptide, as opposed to bound water, salts, and counter-ions from the manufacturing process. Lyophilized peptides commonly carry a meaningful percentage of non-peptide mass.

This is one of the most overlooked fields on a COA. Purity tells you the quality of the peptide present; net content tells you the quantity. Both matter.

Safety and contamination screens

A thorough COA goes beyond identity and purity to check for things that should not be there:

Endotoxin (bacterial contamination), often reported in EU/mL.
Heavy metals, screened by ICP-MS.
Sterility results.
Residual solvents from synthesis.

Not every certificate includes all of these, and the appropriate panel depends on the intended research use. But the presence of contamination screening is a strong signal that the supplier takes documentation seriously.

Verification: can you trust the certificate itself?

The last question is whether the COA is genuine. Good certificates include:

A signature or named lab director.
A verification code or QR link back to the testing lab’s portal, so you can confirm the certificate was actually issued.
Accreditation marks, such as ISO/IEC 17025, which indicate the lab operates to a recognized standard.

A certificate you cannot verify is only as trustworthy as the person who handed it to you.

A quick checklist

When you open a COA, confirm it has:

A lot number that matches your vial.
Identity confirmed by MS or HPLC.
A stated purity percentage with the method noted.
Net peptide content, not just purity.
Any relevant contamination screens.
A way to verify the certificate with the issuing lab.

If all six are present, you are holding real documentation. If several are missing, you are holding a graphic.

Why this matters

The research value of any compound starts with knowing what you actually have. A clear, verifiable Certificate of Analysis is what turns a vial of white powder into a documented research material. Reading one well is a small skill that pays off every time you order.

Meridian Research Co. publishes lot-level documentation for its compounds. All products are supplied for laboratory research use only and are not for human or veterinary use.

How to Read a Certificate of Analysis (COA) for Research Peptides