How to Read a Peptide COA: HPLC vs LC-MS, 99% Purity, and Spotting Fake Certificates

In plain words, before we get technical

Think of a COA like a report card for one specific batch. It should say who graded it (the lab), which batch it was (the lot number on your vial), how clean it was (purity) and whether it’s really the thing on the label (identity). If you only remember one thing: the lot number on the report has to match the lot number on your vial. Everything below just explains that in more detail, and you can skip straight to the checklist table if you like.

Why the certificate matters more than the label

Two vials can carry the same printed name, the same size and the same “99% purity” claim, and contain very different things. A label is a promise. A certificate of analysis (COA) is the evidence behind it: a report from a testing laboratory saying what it actually measured in a specific sample.

Almost every supplier now says “COA available.” That sentence on its own tells you very little. What matters is whether the certificate is independent, whether it matches the exact batch in your hand, and whether you can check it yourself. This guide explains how to read one the way a lab technician would, how to spot a certificate that proves nothing, and what the numbers really mean.

The five things to check on any COA

If any of these is missing, the certificate is weaker than it looks. If the lot number doesn’t match your vial, it isn’t your certificate at all.

HPLC vs LC-MS: two different questions

These two methods are often listed together, and it’s easy to assume they measure the same thing. They don’t.

HPLC (high-performance liquid chromatography) answers “how pure is it?” The sample is pushed through a packed column, and each component leaves the column at a slightly different time. A UV detector records those components as peaks on a chart called a chromatogram. The size of the main peak relative to all the peaks gives the purity percentage.

LC-MS (liquid chromatography–mass spectrometry) answers “is it the right molecule?” After separation, the mass spectrometer weighs the molecule. Every peptide has an expected molecular mass based on its amino-acid sequence. If the measured mass matches, the identity is confirmed.

Why you want both: HPLC alone can report a beautifully pure sample of the wrong compound. A single clean peak only tells you there is one main substance — not what that substance is. LC-MS alone confirms the molecule is present but doesn’t tell you how much else is in the vial. Purity plus identity is the complete picture.

What “99% HPLC purity” actually means

A result of 99% means that, of everything the UV detector saw, 99% of the signal came from the main peak. The remaining 1% is usually small leftovers from synthesis: shorter or incomplete sequences, or closely related variants.

A few honest caveats a lab technician would add:

• —HPLC purity is not the same as content. Purity describes what share of the peptide material is the right peptide. It doesn’t tell you how many milligrams are in the vial; a separate content or assay test measures that.
• —The method matters. Detection wavelength, column and gradient all affect the number. That’s why a real COA states the method, not just a percentage.
• —Tiny differences above 99% are rarely meaningful between labs. A 99.4% and a 99.7% from two different laboratories are, practically, the same result.
• —A vendor whose every batch reads exactly 99.9% should make you curious, not reassured. Real batches vary.

Across our own published batches, measured purity has ranged from 97.16% to 100%, with a median of 99.63% and 13 of 17 batches at 99% or above. We publish the lower results too. A supplier that only shows its best numbers is showing you marketing.

Batch-specific vs generic COAs

A batch-specific COA is tied to one lot number and one production run. A generic COA is a single certificate reused across many batches, sometimes for years, and sometimes one supplied by a manufacturer for material that has since been repackaged many times over.

A generic certificate can be entirely genuine and still tell you nothing about your vial. Synthesis runs vary. Storage and shipping vary. The only certificate that describes the material you received is the one whose lot number matches the lot printed on it.

How to spot a fake or meaningless certificate

Most misleading COAs aren’t forged from scratch. They are real documents used in a way that implies more than they prove. Warning signs:

• —No laboratory named, or a lab you can’t find or contact.
• —No report number, or a report number the lab can’t confirm.
• —A lot number that doesn’t appear on your vial, or no lot number at all.
• —Purity only, with no identity test, for a compound where identity matters.
• —A chromatogram that looks identical across several different compounds.
• —Test dates that don’t make sense next to the batch, or a certificate years older than the product.
• —Fonts, spacing or numbers that look edited, especially in the purity or batch fields.
• —A “COA” that is just a product page graphic rather than a laboratory report.

Some laboratories let anyone check a report directly on their own website using a verification key printed on the certificate. When that option exists, use it. It is the strongest check available, because it bypasses the seller entirely.

Independent labs, and why we name them

A certificate is only as independent as the lab behind it. We name ours. Most of our published batches are analysed by TESTIDES, an independent peptide-testing laboratory that isn’t part of our supply chain. A few batches carry certificates from other independent labs, and we say so openly: our FOXO4-DRI batch was analysed by Janoshik Analytical, which offers public verification on its own site, and our Cagrilintide batch comes with an HPLC-only certificate from TrustPointe, supplied with the batch.

Those certificates aren’t identical, and we don’t describe them as if they were. An HPLC-only panel measures purity and content but doesn’t include LC-MS identity, so we list exactly which tests each batch received. You can see the method list for every batch on our lab results page.

What about endotoxin testing?

Endotoxins are fragments of bacterial cell walls. They matter most in cell-culture work, where even small amounts can trigger responses that confound an experiment. The standard test is the LAL (Limulus amebocyte lysate) assay, reported in endotoxin units (EU).

To be direct: endotoxin testing is not part of our standard third-party panel, which covers HPLC purity, LC-MS identity, appearance and sterility. If your work is endotoxin-sensitive, treat any research peptide as untested for endotoxin unless its certificate reports an LAL result, and plan your own testing accordingly. Be wary of suppliers who list “endotoxin tested” without showing the result on a batch-specific report.

How to verify one of our batches in 30 seconds

• —Find the lot number printed on your vial label.
• —Enter it into our batch verifier.
• —The matching certificate opens, with the lab, test date, measured purity and methods — and a link to the original PDF.
• —Compare the lot number on the PDF to your vial. They should match exactly.

If anything doesn’t line up, write to sales@popularpeptides.ca. We would rather hear about it than have you guess.

Frequently asked questions

How do I read a peptide COA?

Check five things: the compound and size match your vial, the batch or lot number matches your vial, purity measured by HPLC, identity confirmed by LC-MS, and a named independent lab with a report number and test date you can check.

What is the difference between HPLC and LC-MS?

HPLC measures purity: what share of the sample is the main compound. LC-MS confirms identity by measuring the molecule’s mass. HPLC alone cannot tell you whether the pure substance is the right one, so a strong certificate includes both.

What does 99% HPLC purity mean?

It means 99% of the material detected by the HPLC method was the intended peptide, and about 1% was related impurities such as incomplete sequences. It describes purity, not the number of milligrams in the vial.

How can I tell if a peptide certificate of analysis is fake?

Look for a named, contactable lab, a report number, a lot number that matches your vial, an identity test, and a real chromatogram. Be cautious of certificates with no lab, no lot number, reused chromatograms, or implausibly identical results across batches. Where the lab offers online verification, use it.

What is a batch-specific COA?

A certificate tied to one lot number and one production run. It describes the actual material in vials carrying that lot number, unlike a generic certificate reused across many batches.

Are Popular Peptides batches third-party tested?

Yes. Every published batch has an independent laboratory certificate — most by TESTIDES — that you can look up by lot number at popularpeptides.ca/verify. Each record lists exactly which tests that batch received.

Is endotoxin testing included?

No. Our standard panel covers HPLC purity, LC-MS identity, appearance and sterility. Endotoxin (LAL) testing is not included, so endotoxin-sensitive work should plan its own testing.

The bottom line

A certificate is only useful if it’s independent, specific to your batch and checkable by you. Read the lot number first, then purity, then identity, then who did the testing. If you’re buying in Canada and weighing a domestic supplier against an import, our guide to Canadian vs imported research peptides covers the shipping side. New to all of this? Start with our plain-language guide.

All Popular Peptides products are supplied for in vitro laboratory research use only. They are not medicines and are not intended for human or veterinary use. Testing described here measures analytical quality and identity; it is not a statement about any biological effect.