Potency

What it determines

Potency uses the same chromatographic separation as purity, run quantitatively. A reference standard of known content is injected across a series of concentrations to build a calibration curve of peak area against amount injected.

The sample is weighed, dissolved to a known volume, and injected under the same conditions. Its main-peak area is read against that curve to give the mass of peptide present, which is then expressed as a fraction of the sample mass taken. This is the figure that answers how much peptide the vial holds.

Practical notes

• The weighing basis matters. Water, counter-ion, and salt all contribute to the gross mass of a lyophilized cake, so content figures sit below purity figures for most material.
• Vials that have been opened and re-closed take up moisture, which moves the mass basis. Sealed, unopened vials give the cleanest result.