HPLC Purity Testing: What “99%+” Actually Means

HPLC purity testing is the standard way to measure the purity of lab-made compounds. HPLC stands for high-performance liquid chromatography. So, when a report says “99%+”, HPLC is almost always where that number comes from.

How HPLC purity testing works

First, the lab dissolves a small sample. Then, a pump pushes it under high pressure through a column packed with fine beads. Different molecules travel through the column at different speeds. As a result, they leave it at different times. Finally, a detector at the end records each one as a peak on a chart.

Reading the chromatogram

Labs call this chart a chromatogram. In a clean sample, one large peak stands out. Meanwhile, smaller peaks show other compounds, such as short chains left over from synthesis. In HPLC purity testing, the lab works out purity by dividing the area of the main peak by the total area of all peaks.

What HPLC purity testing does and does not tell you

• It tells you how much of the detected material is the target compound.
• However, it does not confirm identity on its own. That is the job of mass analysis.
• Also, it does not measure bacterial endotoxins, which need a separate test.

In short, a high purity figure is a good start, but it is not the whole story. For this reason, careful labs look at the full set of reports together.

Why independent testing matters

HPLC purity testing is only as reliable as the lab that runs it. So, reports from an independent lab carry far more weight than an in-house claim. Even better, a report with a check link lets you confirm it yourself. You can learn more about the method on Wikipedia. You can see the reports for each current batch on our Lab Results page. Then, compare them with our guide on reading a COA. For lab research use only. Not for human or animal use.