Analytical methods
What a 99% purity number does not tell you
A 99% figure describes the light absorbed at one wavelength, not the mass in the vial. Here is what HPLC misses, and which tests close each gap.
Section
Analytical methods
How labs check what is in a vial, and what each test can and cannot show.
Analytical methods
Weighing a peptide: how mass testing confirms what you have
Measured mass against calculated mass. A gap of +16, +42, +71 or −18 daltons each points at a specific, well-known cause.