“99% pure” sounds great — but pure of what, measured how? A plain-English look at the gold-standard purity test and how to read the graph instead of trusting a headline number.
HPLC — high-performance liquid chromatography — is the gold-standard test for peptide purity. In plain English, it answers one question: of everything in this vial, what percentage is the peptide you ordered, and what percentage is something else?
The sample is dissolved and pushed at high pressure through a column packed with a fine material. Different molecules travel through at different speeds, so they exit at different times. A detector records each one as it comes off, drawing a graph of peaks called a chromatogram. The target peptide shows up as one dominant peak; impurities show up as smaller peaks elsewhere.
You do not need a chemistry degree to sanity-check one. Look for three things:
Purity percentages are not arbitrary. In a research context, these are the rough tiers vendors and labs work with:
Higher is better, but the number only means something when it is batch-specific and backed by a chromatogram from a named third-party lab. A 99% claim on a fabricated or recycled certificate is worth less than a verified 98%.
Here is the most important thing to understand about HPLC: it tells you how pure the material is, but not whether it is the right molecule, and not whether it is clean of contamination. A vial can be 99% pure of the wrong peptide, or 99% pure and still carry bacterial endotoxins. Those need different tests.
That is why serious vendors publish a full testing stack, not just a purity figure. Here is how mass spec and endotoxin testing fill the gaps HPLC leaves.
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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