Understanding HPLC purity
What the HPLC purity percentage on a COA measures, how it's worked out, and what it can't tell you.
HPLC purity is the number most researchers look at first on a certificate of analysis. Here's what it measures, and just as important, what it doesn't.
What HPLC is
High-performance liquid chromatography (HPLC) is a lab technique that separates the parts of a sample. The sample is dissolved and pushed under pressure through a packed column. Different substances move through the column at different speeds, so they come out at different times. A detector records each one as a peak on a chart called a chromatogram.
How the purity percentage is worked out
The main peak belongs to the named compound. Smaller peaks are other substances in the sample, such as related impurities. Purity is usually reported as the area of the main peak as a share of the total area of all peaks.
So "99.4% HPLC purity" means that, under that method, 99.4% of what the detector measured was the named compound.
What the number doesn't tell you
- Identity. HPLC shows how much of the sample is the main substance. It doesn't by itself prove which substance that is. Identity is confirmed with other methods, such as mass spectrometry.
- Sterility or endotoxin. Microbial contamination and bacterial endotoxin need their own tests.
- Anything outside what the detector sees. Water, salts and other substances the method isn't designed to detect aren't counted in the percentage.
- Effects or safety. Purity is an analytical result for a batch, not a statement about any use.
Why methods matter
Results depend on the method: the column, the conditions and how the method was validated. Guidance from the International Council for Harmonisation (ICH Q2) sets out how analytical procedures are validated, including specificity, accuracy and precision. Comparing purity numbers is most meaningful when they come from similar, validated methods.
Where to find it for your vial
Every published Genesis lot shows its HPLC purity in the COA library and on the product page. Search the batch number on your label to see the result for your exact vial.