DEMO=0 python3 build.py after wiring real content.HPLC measures how much. Mass spectrometry tells you what. A certificate with only one of them is half a result.
A separation technique with a UV detector. It quantifies. It is blind to identity — a perfect 99% peak can be the wrong molecule entirely.
The liquid chromatograph feeds a mass spectrometer, which measures the mass-to-charge ratio of the eluting ions. A peptide of the wrong sequence has a different mass, and it shows immediately.
A cheaper analogue elutes near the same time and integrates as a single clean peak. Purity looks excellent because purity was never the question being asked.
Identity plus purity plus content. One without the others is a number looking for a question.