High-performance liquid chromatography is the industry standard for measuring peptide purity. Here's how it works and what the number really tells you.
High-performance liquid chromatography (HPLC) separates the components of a sample by pushing it through a column under high pressure. Different molecules travel through the column at different speeds, so the target peptide and any impurities emerge at different times and are recorded as distinct peaks.
The purity figure you see on a Certificate of Analysis is derived from the area of the main peak relative to the total area of all peaks. A 99%+ result means the target compound accounts for at least 99% of the detected material.
What HPLC Does and Doesn't Tell You
HPLC is excellent at quantifying how much of your sample is the intended compound versus everything else. What it does not do on its own is confirm the identity of that main peak — that a peak is 99% of the sample does not prove the peak is the molecule you ordered.
- HPLC answers: how pure is this sample?
- Mass spectrometry answers: is this actually the right molecule?
- Together, they give you both purity and identity — which is why we run both.
Why We Hold the Line at 99%
It is common to see research material advertised at 95% or 98%. Those are respectable numbers, but the last few percentage points matter. A 4% impurity load is four times the uncontrolled variation of a 1% load. For work that needs to be reproducible, we treat 99%+ as the floor, not the goal — no batch ships below it.
This article is provided for educational and research context only. All products referenced are intended strictly for laboratory and research use — not for human consumption, medical, veterinary, or household use.