A test report usually lists two analytical methods together - HPLC and LC-MS - because they answer different questions. Reading a certificate is easier once you know which answer comes from which method.
HPLC - how much
High-performance liquid chromatography separates the components of a sample as they pass through a column, and a detector (commonly UV) measures each as a peak. The area of the main peak versus the rest gives the purity percentage. HPLC is a quantity-and-separation question: how much of the main component is present, and how much is something else.
LC-MS - what it is
Liquid chromatography-mass spectrometry adds a mass detector. After separation, the mass spectrometer measures the mass of the molecule, which is used to confirm identity - whether the compound is actually the intended one. HPLC can show a clean, single peak that is still the wrong molecule; LC-MS is what closes that gap.
Why both
Purity without identity is a number with no anchor; identity without purity says nothing about how much unwanted material is present. Together, HPLC and LC-MS state both what the compound is and how much of it the batch contains - which is why a serious test report reports both.