HPLC is the workhorse test on every peptide Certificate of Analysis. This guide explains in plain English what HPLC actually measures, how to read a chromatogram, and what HPLC cannot tell you.
What HPLC is
High-Performance Liquid Chromatography (HPLC) pushes a dissolved sample through a column packed with a chemical "stationary phase". Different molecules in the sample interact with the stationary phase differently, so they exit the column at different times. A detector at the end records each component as a peak on a chromatogram.
What HPLC measures
Purity: the labelled peptide's peak area as a percentage of all peaks on the chromatogram.
Peptide content: when run against a calibration standard (quantitative HPLC), the absolute mg of peptide in the vial.
Impurity profile: the size and number of impurity peaks gives a fingerprint of the synthesis quality.
How to read a chromatogram
A peptide HPLC chromatogram is a graph: time on the x-axis, detector signal on the y-axis. A good chromatogram has one tall peak at the expected retention time, with small or no other peaks. A messy chromatogram with multiple peaks of comparable size is a low-purity result regardless of the headline percentage.
What HPLC does NOT tell you
What the peptide actually is. HPLC says "this peak is 98% of the sample", not "this peak is retatrutide". You need LC-MS for identity.
Sterility. HPLC ignores bacteria and endotoxins entirely.
Biological activity. Pure peptide can be inactive if folded wrong; HPLC doesn't detect this.
What good HPLC results look like
Research-grade peptides typically test at 97-99% HPLC purity. The pass threshold LabDoc uses is 95%. Pharmaceutical-grade product is generally ≥99.5%.
Where to see real HPLC results
Every result on the LabDoc results feed includes the HPLC purity percentage, and the original lab CoA, including the chromatogram trace, is linked from each result.
Frequently asked questions
Is HPLC the same as LC-MS?
No. HPLC separates and quantifies; LC-MS adds a mass spectrometer to identify what each peak actually is. Most complete CoAs run both.
What HPLC purity should I expect?
Research-grade peptides are typically 97-99% by HPLC. LabDoc's pass threshold is 95%; anything under that is treated as low purity.
Can a vial be 99% HPLC pure but mostly mannitol?
Yes: HPLC measures the peptide fraction's purity, not the vial's peptide content. Quantitative HPLC against a reference standard is needed to confirm actual mg per vial.