What Is HPLC Purity? What 99% on a Peptide Means
App Library Tools Pricing Download
[Glossary · Quality, storage and rules]

HPLC purity

Also called HPLC, high-performance liquid chromatography, purity percent, peptide purity · Reviewed

Definition: HPLC purity is the percent of a sample that is the intended compound, measured by high-performance liquid chromatography (HPLC). HPLC pushes a dissolved sample through a packed column so each substance comes out at a different time; a detector draws each one as a peak. Purity is the target peak's share of all peaks.

Worked example: reading a purity number

98% purity on a 10 mg vial

  1. The COA says HPLC purity 98%. Of everything the detector saw, the target peptide made up 98% of the peak area.
  2. The other 2% is other material, often related peptides formed while the peptide was made or as it aged.
  3. It does not say the vial holds 10 mg. Amount is a separate test, often called content or assay.
  4. It does not say anything about sterility or endotoxin.

FDA guidance on generic semaglutide shows how seriously impurities are taken: it asks makers to identify every peptide-related impurity above 0.5% of the drug substance and compare them against the brand product.

What HPLC alone cannot tell you

HPLC shows that there is one main peak. It does not prove the main peak is the right molecule. That is why identity is usually confirmed with mass spectrometry, often in the same run (LC-MS). When researchers looked closely at a product sold as TB-500, HPLC with mass spectrometry identified a short fragment of thymosin beta 4 in it (Esposito 2012).

A number printed on a label is not the same as a number someone measured. In one study, semaglutide vials claiming 99% purity measured 7.7% to 14.37% (Ashraf 2024).

Why it matters when you track doses

Your dose math assumes the vial holds what the label says. Keep the COA lot number with the vial in your log, so a surprising result can be traced to a batch.

Read more on Dose Track: TB-500

General education drawn from labels and published studies, not personal medical advice. Your prescriber, pharmacist and the label that came with your product are the final word.
Certificate of analysis (COA)A certificate of analysis (COA) is a document listing test results for one batch (lot) of a product: what… Mass spectrometry (MS)Mass spectrometry (MS) is a lab method that weighs molecules. It turns molecules into charged particles… EndotoxinEndotoxin is a substance from the outer wall of certain bacteria (gram-negative bacteria), released when… Research use only (RUO)Research use only (RUO) is a label phrase. In US rules it comes from labeling for in vitro diagnostic…

Frequently asked questions

Is 99% HPLC purity good?+
It means 99% of what the detector saw was the target peak. It does not confirm identity, amount, sterility or endotoxin, and it is only as reliable as the lab that ran it.
What is LC-MS?+
Liquid chromatography joined to mass spectrometry. The LC part separates the mixture and the MS part weighs each piece, so one run checks both purity and identity.

Sources

  1. FDA draft product-specific guidance on semaglutide (July 2026): impurity thresholds for generic peptides
  2. Esposito et al. Drug Test Anal 2012 (a thymosin beta 4 fragment identified in TB-500 by HPLC with mass spectrometry). PMID 22962027
  3. Ashraf et al. J Med Internet Res 2024 (semaglutide vials bought online without a prescription: LC-MS, sterility and endotoxin tests). PMID 39509151

All glossary terms · Goals and conditions · Compound guides · Help center