HPLC and LC-MS: what each method actually shows

Chromatographic separation tells you how many components are present and in what relative proportion under the conditions used. Mass spectrometry tells you about the mass of what eluted. These are complementary, not interchangeable.

A purity figure derived from a UV chromatogram is relative to what absorbs at the chosen wavelength. Components that do not absorb are invisible to that measurement, which is why a single figure should always be read alongside the stated method.

Mass data adds identification confidence but says little about relative quantity unless the method was designed for quantification.

In practice, reading both together — and reading the method conditions before the numbers — is what makes an analytical report useful rather than decorative.