Purity vs. net-peptide content: what the number actually means.

Two peptide vials can both say “99% pure” and hold wildly different amounts of peptide. That's not a contradiction — it's the difference between purity and content, and it's the most commonly confused thing on a peptide COA. Here's the distinction, and why it changes how you read a certificate.

Purity answers “how clean,” not “how much”

Chromatographic purity is the area-percent of your target peak relative to everything else the analysis resolves. A 99% purity result means that, of what the column separated and the detector saw, 99% was your compound and 1% was other resolved material. It's a statement about quality— how much of what's in the vial is the thing you wanted, versus impurities.

What purity does not tell you is how much peptide is actually there. It's a ratio, not a quantity. A nearly empty vial and a full one can both be 99% pure.

Net-peptide content answers “how much”

Net-peptide content(also called net-peptide assay) is the actual mass of peptide in the vial, in milligrams, quantified against a certified reference standard. This is the number that tells you whether a vial labeled “10 mg” contains 10 mg — or 7.

This matters because peptide isn't the only thing in a lyophilized vial. Counterions, residual water, and excipients all add mass. A vial can weigh the “right” amount on a scale and still be well short on actual peptide. Purity won't catch that. Only a content assay will.

Why a 99% pure vial can still be underfilled

Imagine a vial that's genuinely 99% pure by HPLC — the peptide present is clean. But it was filled with 6 mg of peptide, not the 10 mg on the label, with the rest of the vial mass made up of salt and water. Purity: excellent. Content: 40% short. If you dose by the label, you're dosing 60% of what you think you are — and a purity-only COA would have told you everything looked perfect.

That's the gap. Purity describes the quality of the peptide that's present; content describes how much peptide is present. You need both numbers to know what you actually have.

Why KMD reports both

On every certificate, KMD reports chromatographic purity (area %) and net-peptide assay (mg per vial), alongside a reference-standard identity confirmation — all by RP-HPLC-UV, against certified reference standards. We report the milligram figure because a purity percentage alone leaves the most practical question — how much peptide did I actually get? — unanswered.

And because every COA we issue is SHA-256 verifiable, those numbers can't be quietly edited after the fact without the tampering being detectable.