How to read a peptide certificate of analysis

What HPLC purity actually measures

High-performance liquid chromatography separates the contents of a sample by how strongly each component sticks to a column. The detector output is a chromatogram: a baseline with peaks rising out of it, one peak per component that came off the column at a distinct time.

Purity by HPLC is an area calculation. The software integrates the area under every peak, then reports the target peptide's peak as a percentage of the total. "99.2% by HPLC" means the main peak accounts for 99.2% of the total detected peak area, and everything else — synthesis by-products, truncated sequences, residual reagents — accounts for the remaining 0.8%.

This is worth being precise about, because it is the single most misread number in the industry: HPLC purity tells you how much of what is in the vial is one dominant thing. On its own it does not tell you that the dominant thing is the peptide named on the label.

What mass spectrometry adds, and why identity is a separate question

Mass spectrometry measures mass-to-charge ratio, which gives you the molecular weight of what you are looking at. Compared against the theoretical weight of the intended sequence, it answers a different question than HPLC: not "how pure?" but "is this the right molecule?"

The two tests are complementary and neither substitutes for the other. A sample can be 99% one compound and that compound can be the wrong one; MS is what closes that gap. A full analytical package for a research peptide typically pairs HPLC purity with an MS identity confirmation.

Our certificates do not include a mass-spec run. They are HPLC purity and related substances, plus water content by Karl Fischer and a bacterial-endotoxin pass/fail. We would rather say that plainly than let the word "verified" imply a test that was not performed.

What "third-party tested" means, and what ours are

"Third-party tested" means an independent laboratory — one with no commercial stake in the result — ran the assay and issued the certificate. The reason independence is treated as the gold standard is structural rather than technical: a seller grading its own product has an incentive problem, however good its instruments are.

Ours are not third-party certificates. Every certificate we publish is issued by the manufacturer's QC laboratory (Qingdao Hongtai Biology Co., Ltd), and the stamp is visible on the certificate image itself. We publish the image rather than a retyped table specifically so you can see whose name is on it.

That is a weaker form of evidence than an independent assay and we are not going to describe it as anything else. What it is good for: it is lot-matched, it is legible, it is the document the material actually shipped with, and you can compare the batch number on it against the batch number on your vial. What it is not: proof from a party with nothing to gain.

Reading a certificate in order

Start with identity. Does the product name on the certificate match the vial, and does the batch or lot number match exactly? A certificate that does not tie to the specific vial in your hand is a document about some other material.

Then the test date and the issuing laboratory. A certificate dated well before the batch was synthesised is describing a different batch. The issuing lab tells you which kind of evidence you are holding — manufacturer QC or independent.

Then the HPLC result, and the chromatogram if one is supplied. You want one clearly dominant peak. A cluster of large secondary peaks near the main one often indicates closely-related synthesis by-products such as deletion sequences.

Then the supporting lines: related substances as a total percentage, water content (lyophilised peptide is hygroscopic, and water is mass you are paying for but not receiving as peptide), and whatever the certificate says about bacterial endotoxin. Ours records a pass against a not-more-than 10 EU/mg specification; it is not a measured figure, and a certificate that gives a number is telling you more than one that gives a verdict.

Red flags

A purity percentage with no certificate behind it. A number in marketing copy is a claim, not a measurement.

A retyped table instead of the laboratory's own document. Transcription is where inconvenient details go missing, which is why we publish the certificate image.

No lot number, or a lot number that does not match the vial. Also worth checking: whether two different products somehow carry the same batch number. A batch number that identifies two products identifies neither.

Testing dated years before the batch, or a certificate with no date at all.

A supplier describing manufacturer QC certificates as third-party. If a supplier is loose about who ran the test, the specific figures on the certificate are not the thing you should be worrying about.

Frequently asked

What purity should a research peptide be?

Reference-grade material is typically reported at 98% or better by HPLC, with the chromatogram available so the number can be checked against the trace it came from. The percentage on its own is less informative than the chromatogram plus a matching lot number.

Is HPLC purity enough on its own?

No. HPLC answers how pure the material is; mass spectrometry answers whether it is the intended molecule. A complete analytical package pairs both. Our certificates cover HPLC purity and related substances, not mass-spec identity.

Are Pure North's certificates third-party?

No. They are the manufacturer's QC certificates, issued by Qingdao Hongtai Biology Co., Ltd, and we publish the certificate images so the issuing laboratory is visible. We do not describe them as independent or third-party.

What is on the certificates you publish?

Batch number, HPLC purity, related substances, water content by Karl Fischer, and a bacterial-endotoxin pass/fail against a not-more-than 10 EU/mg specification. There is no mass-spec identity run.

How do I match a certificate to my vial?

Compare the batch or lot number printed on the certificate against the one on the vial label. If they do not match exactly, the certificate describes different material.

Referenced in our catalog

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