When a peptide is described as “98% pure,” that number comes from a specific test: HPLC. Understanding what purity means — and how it’s measured — helps you compare research material with confidence. Here’s a plain-language primer.
- Purity = the percentage of a sample that is the intended peptide.
- HPLC (high-performance liquid chromatography) is the standard purity test.
- Identity is confirmed separately, usually by mass spectrometry.
- Both appear on a Certificate of Analysis.
What “purity” actually means
No synthesized peptide is 100% a single molecule — tiny amounts of by-products remain after purification. Purity expresses how much of the sample is the target peptide versus everything else. A higher figure means fewer impurities and more consistent research results.
How HPLC measures it
In HPLC, the sample is pushed through a column that separates its components based on how they interact with the column material. Each component emerges at a different time, producing a series of peaks. The size of the main peak relative to the total tells you the purity.
- The main peak represents the target peptide.
- Smaller peaks are impurities or by-products.
- Purity % = area of the main peak ÷ total peak area.
Purity vs identity
Purity and identity answer different questions. HPLC tells you how much of the sample is your peptide; mass spectrometry confirms the peptide is the right molecule. A trustworthy vial reports both.
| Question | Test |
|---|---|
| Is it the right molecule? | Mass spectrometry (identity) |
| How much is the target? | HPLC (purity) |
| Where is it documented? | Certificate of Analysis |
Related reading: how peptides are made and how to read a COA.
Every batch we sell is HPLC-tested
Third-party purity verification on each lot.