How to Read a Peptide Certificate of Analysis (and Spot a Fake One)

The Purity Number Is the Least Useful Part

Almost every peptide listing quotes a purity figure. Almost nobody reads the document behind it. This is backwards, because a purity percentage on its own is close to meaningless, and the sections most buyers skip are the ones that actually tell you whether the vial contains what the label claims.

Here is how to read the document properly.

What HPLC Purity Actually Measures

Reversed-phase HPLC separates the compounds in a sample and measures UV absorbance as each one comes off the column, typically at 214–220nm (the wavelength where the peptide bond absorbs). The chromatogram plots that absorbance over time. Purity is then calculated as area under the main peak, divided by total area under all peaks.

Read that definition again, because three things follow from it that the marketing never mentions:

It is a relative measure, not an absolute one. "98% pure" means the main peak accounts for 98% of the UV-absorbing material the detector saw. It says nothing about material that does not absorb at that wavelength — residual salts, solvents, and water are largely invisible to this method.

It does not tell you what the peak *is*. A 99% pure peak of the wrong molecule is 99% pure. HPLC separates and quantifies; it does not identify. Which brings us to the section most fake CoAs omit entirely.

It says nothing about biological safety. Purity is not sterility. It is not endotoxin load. It is not bioburden. A sample can be 99% pure by HPLC and heavily contaminated with bacterial endotoxin, because endotoxin does not show up as a peak on a reversed-phase chromatogram.

Mass Spectrometry Is the Section That Matters Most

If a CoA has HPLC but no mass spec, treat it as incomplete.

Mass spectrometry measures the molecular weight of the compound. Every peptide has a theoretical molecular weight computed from its amino acid sequence. The MS result should match it, within a small tolerance.

This is the only section on the document that answers the question *"is this actually the compound on the label?"* HPLC tells you the sample is clean. MS tells you it is the right molecule. You need both, and of the two, identity is the more fundamental claim.

An MS trace showing an observed mass that matches the theoretical mass is difficult to fake convincingly and expensive to fabricate. It is, not coincidentally, the section most often missing from forged documents.

Net Peptide Content: The Number Nobody Talks About

This is the single most under-discussed figure in the entire industry, and it is where a lot of buyers are quietly losing 20–30% of what they paid for.

A vial labelled "10mg" contains 10mg of lyophilised powder. That powder is not 100% peptide. It also contains:

• •Counterion — most synthetic peptides are purified as a trifluoroacetate (TFA) or acetate salt. The counterion is bound to the peptide and can account for a substantial fraction of the mass.
• •Residual water — lyophilised powder is hygroscopic and retains bound water.
• •Residual salts and solvents from synthesis and purification.

Net peptide content (sometimes "peptide content" or "assay") is the percentage of the powder mass that is actual peptide. It is typically determined by amino acid analysis or nitrogen determination, and for a typical synthetic peptide it lands somewhere around 70–85%.

So consider two vials:

Vial A looks worse on the headline number people compare. Vial A is the honest one. Vial B is not telling you what you are buying.

Most vendors do not report net peptide content, and most buyers do not ask. If you want one question to ask a supplier that will immediately tell you how serious they are, this is it.

What a Complete CoA Contains

The three in bold are the ones to check first.

Forgery Tells

Fabricated CoAs are common. They are also, usually, lazy. The following tells cost you nothing to check:

The batch number does not match your vial. This is the most common failure and the easiest to catch. A CoA is a document about *one specific batch*. If the vendor sends you a generic CoA with no lot number, or a lot number that is not printed on the vial in your hand, the document is not evidence about your product. It is decoration.

The chromatogram is an image with no axes. A real chromatogram has a labelled time axis, an absorbance axis, retention times marked on the peaks, and usually an integration table. A cropped, low-resolution peak shape with no numbers is a picture of a chromatogram, not a chromatogram.

The same chromatogram appears across different products. Peak shape and retention time are effectively a fingerprint of a specific run. If a vendor's BPC-157 and their TB-500 have visually identical traces, one document was copy-pasted. Open two CoAs from the same vendor side by side and compare. This catches a surprising number of them.

Purity is stated but no data is attached. "99.2% purity" as a line of text on a website, or in a PDF with no chromatogram, is a claim, not a result.

PDF metadata is inconsistent. Right-click, check document properties. Creation date after the stated analysis date, an author field naming the vendor rather than the lab, or a document produced in image-editing software rather than an instrument's reporting package are all worth a second look.

Nobody is named. A real testing lab puts its name on its work. Anonymous CoAs are anonymous for a reason.

Third-Party Testing Beats Supplier-Supplied Documents

A CoA supplied by the seller is a document produced by the party with the strongest incentive for it to say something specific. That does not make it false — most are genuine — but it does mean it is not independent evidence.

Independent, buyer-commissioned testing through an analytical lab is the only way to fully close the loop. In this space Janoshik Analytical is the most widely used third-party option, and results sent directly from the lab to the buyer cannot be intercepted and edited in between. That last detail is the entire point: a CoA that reaches you *via the vendor* has passed through the vendor's hands.

If a supplier volunteers independent third-party results without being asked, that is a meaningful signal.

So What Purity Is Actually Acceptable?

For research-grade synthetic peptides, ≥98% by HPLC is the practical standard, and most reputable synthesis houses hit 98–99%.

But rank your questions in this order, because the sequence matters more than the threshold:

1. Is it the right molecule? (mass spec) — a wrong compound at 99% purity is worthless and potentially dangerous.

2. How much peptide am I actually getting? (net peptide content) — determines what you paid for.

3. How clean is it? (HPLC purity) — 98% vs 99% is a far smaller practical difference than most forum arguments suggest.

4. What is in the impurity fraction? — 2% of a benign truncated sequence is not the same as 2% of something else. The chromatogram shows you whether the impurities are a few small peaks near the main one (typically deletion sequences from synthesis) or something structurally unrelated.

A vendor who can answer 1 and 2 without hesitating is telling you a lot about how they operate.

Disclaimer: This information is provided for educational purposes relating to laboratory research quality control. All products are supplied strictly for in-vitro laboratory and research use. Not intended for human consumption. Not medical advice.