Purity is only one of four questions. Identity, contamination, and traceability each answer something HPLC can't — and one of them is the reason high purity doesn't mean a vial is clean.
People talk about peptide testing as if it is one thing. It is not. A complete quality picture comes from four separate tests, and each answers a question the others cannot. Miss one and you have a blind spot.
A white powder in a vial looks identical whether it is the peptide you ordered or a cheaper substitute. HPLC can tell you the sample is 99% pure — but pure of what? Mass spectrometry answers that. It measures the molecular weight of the compound and compares it to the known weight of the target peptide. If they match, you have the right molecule. If they don't, you caught a bait-and-switch that purity testing would have sailed right past.
This is why credible COAs show both an HPLC purity figure and MS identity confirmation. One without the other leaves a real question unanswered.
This is the single most overlooked test, and the most important hook to understand: HPLC and mass spec cannot detect endotoxins. Endotoxins are fragments of bacterial cell walls. They can be present even in a sample that tests 99% pure and confirms the correct identity, because they are a different kind of contaminant entirely.
The test that catches them is the LAL assay (Limulus Amebocyte Lysate) — the standard endotoxin screen. A vendor that publishes HPLC and MS but is silent on endotoxin has only answered two of the three quality questions. In a research context where sterility matters, that gap is worth noticing.
Even a perfect set of test results is meaningless if it does not match the vial in front of you. Batch traceability is the lot number that connects this specific production run to these specific test results on a dated certificate. Without it, a vendor can run one good batch, publish its COA forever, and ship whatever they like afterward — the “free-sample trap” in our scam-vendor guide.
When you can match the lot number on the vial to the lot number on a recent, batch-specific COA, all four tests finally mean something.
Once you know what quality looks like on paper, the next step is finding vendors that actually meet the bar. That is exactly what our rankings measure.
Last reviewed July 2026. By the Peptides Uncaged Research Team. For research and educational purposes only.
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