How HPLC purity testing works
What a purity percentage actually measures, and how to read the chromatogram behind it.
What the number means
A purity figure from reverse-phase HPLC is the area of the main peak as a share of total peak area at a given wavelength. It describes what the detector saw, not an absolute statement about the contents of the vial.
Why the method matters
Column chemistry, gradient and detection wavelength all change the result. A credible certificate names the method, so two lots can be compared on the same basis.
Identity is separate
HPLC shows how clean a sample is; mass spectrometry shows what it is. A lot should carry both, because a very pure sample of the wrong compound is still the wrong compound.