What Is HPLC Purity on a Peptide COA?
HPLC purity is the most commonly reported measurement on peptide Certificates of Analysis. Here is what it actually measures, and what it does not.
HPLC stands for High Performance Liquid Chromatography. It is the standard analytical method for measuring purity in research peptides. When a vendor's Certificate of Analysis lists a number like 99.5 percent purity, that figure almost always comes from HPLC.
What HPLC actually measures
HPLC pushes a dissolved sample through a column packed with separation material. Different compounds travel through the column at different speeds and are detected by a UV-Vis detector as they exit. The result is a chromatogram, a graph showing peaks at different retention times. The area under the main peak compared to the total area of all peaks is the chromatographic purity percentage.
What HPLC purity does not measure
Three important things. First, identity. HPLC alone does not confirm the peak is the compound on the label, only that the sample is mostly one substance. Identity requires Mass Spectrometry or molecular weight confirmation. Second, endotoxin. Bacterial endotoxin contamination during synthesis is invisible to HPLC. Third, sterility. Microbial contamination is also invisible to HPLC.
Typical HPLC purity values in the peptide market
Premium vendors with strong manufacturing report above 99 percent. Mid-tier vendors report 97 to 99 percent. Anything under 97 percent in this market is a quality concern. A COA reporting "greater than 99 percent" with no decimal precision usually indicates rounded marketing language rather than a precise measurement.
How to use HPLC purity alongside other tests
HPLC purity is one of three or four tests that should appear on a complete COA. The others are identity confirmation (typically Mass Spectrometry), endotoxin (USP 85), and sterility (USP 71). A vendor reporting only HPLC purity is showing you one third of the picture.
Frequently Asked Questions
Is 99.5 percent purity good for a research peptide?
Yes, 99.5 percent purity is on the higher end of the US peptide market. However, purity alone does not tell you about identity, endotoxin, or sterility, so look for a full panel COA.
What does HPLC-MS mean on a COA?
HPLC-MS combines HPLC purity measurement with Mass Spectrometry identity confirmation in a single run. It is the gold standard for combined purity and identity testing.
Why do some COAs report purity differently?
Different labs use different detection methods (UV at 214 nm, UV at 220 nm, MS detection) and different column types. Variations of 0.1 to 0.5 percent between labs on the same compound are normal.