Every peptide storefront on the internet says 99%. The number is so universal it has become wallpaper. Here is what it actually means when a certificate backs it, and why the method printed next to the number matters more than the number itself.
Where the percentage comes from
Peptide purity is typically reported from high-performance liquid chromatography (HPLC or its faster cousin UPLC). The instrument separates everything in the sample as it flows through a column; each component appears as a peak on a chromatogram. Purity is the area of the main peptide peak divided by the total area of all peaks, expressed as a percent. When our ledger shows Retatrutide lot DPS-8032676 at 99.5% by UPLC/MS, that is the calculation behind it.
What mass spectrometry adds
A chromatogram tells you how much of the sample is one dominant component. It does not, by itself, prove that component is the peptide on the label. That is the job of mass spectrometry: measuring the molecular mass of the main peak and matching it against the expected mass of the sequence. A serious certificate pairs the two, which is why methods like LC-MS/MS appear on the reports in our COA ledger.
Purity is not content
The most misread distinction in the field: purity describes the composition of the peptide material, not how much peptide is in the vial. Lyophilized peptide always includes non-peptide mass, such as bound water and counterions from synthesis. Two vials can both be 99% pure and contain different amounts of net peptide. Purity and quantity are separate questions, answered by separate methods.
How to read a number critically
- No method named? Treat the number as marketing.
- No lot number? The certificate cannot be tied to your vial.
- No laboratory named? In-house claims are not third-party testing.
- Every batch always 99%+? Real testing produces variation; our ledger shows 99.5% and 99.351% because those are the actual results.
Quick answers
Is higher always better? Higher purity means fewer synthesis-related impurities in the material. What matters for documentation is that the number is real, method-backed, and lot-specific.
Why do your products show pending sometimes? Because we publish certificates when they exist, not before. Lots in testing are labeled pending in the ledger.
Where do I check my vial? Match the printed lot number to its entry in the ledger.
For laboratory and in-vitro research use only.
For laboratory and in-vitro research use only. Not for human or veterinary use. See our research-use disclaimer.
