Zeta potential measurement, usually by electrophoretic light scattering, gives researchers an estimate of the surface charge of particles in a peptide preparation and a practical indicator of colloidal stability in solution. What it shows: Values near zero can signal a higher tendency for particles to aggregate, while larger magnitudes are generally associated with greater electrostatic repulsion in the measured system. Results depend strongly on pH, ionic strength, buffer composition, and concentration, all of which must be recorded and controlled. Use in a QC workflow: Zeta potential is typically paired with DLS particle-size data, SEC, and HPLC so charge findings are interpreted alongside size distribution and purity. Run replicate measurements, include a reference standard, and report the dispersant and measurement model used. Limitations: Zeta potential is an inferred, system-dependent value, not a direct purity measurement; it supports, but does not replace, HPLC and mass spectrometry identity and purity testing. Disclaimer: For laboratory research purposes only. Not for human consumption. The methods described are analytical laboratory techniques; no medical or therapeutic claim is made. Citations: Standard electrophoretic light scattering and colloid science methods literature.