How to Read a Peptide Certificate of Analysis (COA)

Why the COA matters more than the price

A peptide is only as useful to your research as its identity and purity. If the compound in the vial isn’t what the label says, or carries significant impurities, every result built on it is in question.

The certificate of analysis (COA) is your first line of defense. It’s the document that shows a specific batch was actually tested, and what those tests found. Knowing how to read one takes about ten minutes to learn and can save months of wasted work.

This guide walks through what a credible peptide COA contains, how to interpret HPLC and mass spectrometry results, and the red flags that should make you look for another supplier.

What a peptide COA should include

A COA is a batch-specific test report. A generic “product spec sheet” that never changes from lot to lot is not a COA. At minimum, a credible certificate lists:

Element	What to look for
Compound name and sequence	Full amino acid sequence, matching the product listing
Lot or batch number	Must match the number printed on your vial
Molecular formula and weight	The theoretical (calculated) molecular weight
HPLC purity	A percentage, ideally with the chromatogram attached
Mass spectrometry result	The observed mass, compared to the theoretical mass
Test date	Recent enough to be relevant to the batch you received
Testing laboratory	Name and contact details of the lab that ran the analysis
Appearance	Physical form, typically a white lyophilized powder

If any of these are missing, ask the supplier for them before you order. A reputable supplier will provide them without hesitation.

Reading HPLC purity

High-performance liquid chromatography (HPLC) answers one question: how much of the sample is the target peptide, and how much is something else?

The sample is pushed through a column that separates its components. A detector records each one as a peak on a chart called a chromatogram. The target peptide should appear as one large, sharp peak. Smaller peaks are impurities, such as truncated sequences, deletion sequences, or leftover synthesis byproducts.

Purity is calculated as the area of the main peak divided by the total area of all peaks. A result of 98% means the main peak accounts for 98% of what the detector saw.

When you review the chromatogram, check that:

• The main peak is clearly dominant and well defined, not broad or split
• The reported purity matches what the chart visually shows
• The detection wavelength is listed (214–220 nm is standard for peptides)

For most research applications, 95% purity is a common baseline, and 98% or higher is preferred for sensitive assays. The right threshold depends on your protocol, so set it before you shop, not after.

Confirming identity with mass spectrometry

HPLC tells you how pure a sample is. It does not tell you what the sample is. A batch can be 99% pure and still be the wrong peptide. That’s why mass spectrometry (MS) matters.

MS measures the mass of the molecules in the sample. The COA should show the observed mass next to the theoretical mass calculated from the sequence. The two should agree closely, typically within about 1 dalton for standard methods like ESI-MS or MALDI-TOF.

A few things to know when reading MS data:

• Peptides often appear as multiple charged ions (for example [M+2H]²⁺), so you may see several peaks that all point to the same molecular weight
• A large gap between observed and expected mass suggests the wrong sequence, a modification, or a degraded sample
• The best COAs include the actual spectrum, not just a number

Together, HPLC and MS give you the two answers you need: it’s the right compound, and there’s very little else in the vial.

Red flags that should stop an order

Not every COA is trustworthy. Watch for these warning signs:

• No lot number, or one that doesn’t match your vial. The document may not describe the batch you received.
• The same COA for every batch. Identical dates, numbers, and charts across lots suggest the testing was done once, or not at all.
• Purity reported with no chromatogram. A number without the underlying data can’t be checked.
• Suspiciously perfect results. A flat 100.00% purity or a chart with no baseline noise is unusual for real analytical data.
• No testing lab named. You should be able to see who ran the test and, ideally, contact them.
• Signs of editing. Mismatched fonts, misaligned text, or blurry areas around key numbers can indicate an altered document.
• Human-use language anywhere. Research peptides are sold for laboratory use only. A supplier whose materials suggest dosing or personal use is not operating as a research supplier.

Third-party vs. in-house testing

Many manufacturers test their own product, and that data has value. But an independent, third-party lab has no stake in the result, which makes its report a stronger form of verification.

The gold standard is a supplier that publishes third-party COAs for every lot and lets you match the report to your vial. If a supplier only offers in-house data, ask whether independent testing is available on request.

Your COA checklist

Before you place an order, confirm:

• The COA lot number matches the product you’ll receive
• HPLC purity meets your protocol’s threshold, with chromatogram attached
• Mass spec shows observed mass matching theoretical mass
• The testing lab is named and independent
• The test date is recent and specific to this batch
• The supplier labels products for research use only

The bottom line

A COA is only useful if you read it. Check that it’s batch-specific, that HPLC and mass spec data are both present and consistent, and that an independent lab stands behind the results. Those three checks filter out most unreliable suppliers.

At Salus Peptides, every lot ships with a batch-specific certificate of analysis, and the traceability is printed right on the vial. Each vial carries two numbers: our lot number, which ties it to its sourced batch and its posted COA, and the accession number assigned by the independent third-party lab that tested that batch. You can look up the accession number on the testing lab’s website and confirm the results yourself. Institutional buyers can contact us to set up an account or request documentation for procurement review.

All Salus Peptides products are intended strictly for laboratory research use. They are not for human or veterinary use, and are not intended to diagnose, treat, cure, or prevent any disease.

Frequently asked questions

What does COA stand for?

COA stands for certificate of analysis. It’s a batch-specific report showing the results of analytical tests performed on a product, such as purity and identity testing.

What is a good HPLC purity for research peptides?

Most research applications use 95% as a baseline, with 98% or higher preferred for sensitive assays. The right threshold depends on your experimental protocol.

What’s the difference between HPLC and mass spec?

HPLC measures purity: how much of the sample is the target compound. Mass spectrometry confirms identity: whether the compound has the expected molecular weight. A reliable COA includes both.

Why does third-party testing matter?

An independent lab has no financial interest in the result, so its findings are a more objective check than a manufacturer’s own testing.

Can I verify a COA myself?

Yes. Confirm the lot number matches your vial, contact the named testing lab to verify the report, and compare the observed mass to the theoretical mass for the sequence.