HPLC purity

The area of a compound's chromatographic peak as a percentage of all detected peak area — a relative measure of what the detector saw, not a statement of how much of the powder is peptide by mass.

High-performance liquid chromatography separates the components of a dissolved sample as they pass through a column at different speeds, and detects them as they elute — for peptides, usually by ultraviolet absorbance in the region where the peptide bond absorbs. The result is a trace of peaks, and purity is calculated as the target peak's area divided by the total detected peak area.

The definition carries a consequence that certificates rarely spell out: the figure is a proportion of what the detector responded to, not a proportion of the vial's contents by mass. Residual water and the counterion left over from purification are part of the powder but largely invisible to the measurement, so a sample can be 99% pure by peak area while containing meaningfully less peptide by weight. The measurement that resolves that difference is net peptide content.

An HPLC figure is most informative when the report also states the method — column, gradient and detection wavelength — because those conditions determine what the run could have resolved. A bare percentage with no method attached is an assertion rather than a measurement.

For research purposes only. Not for human consumption, diagnosis, treatment, or prevention of any condition. Nothing on this page is medical advice.