HPLC
High-performance liquid chromatography separates components under a stated method. Peak area may be used to estimate relative purity, but interpretation depends on the method, detector, integration, and sample preparation.
Mass spectrometry
Mass spectrometry measures mass-to-charge information that can support molecular identity. It does not, by itself, provide every quality attribute relevant to a sample.
Use together
Identity and purity answer different questions. Strong documentation clearly names the method, result, sample, and limitations of each analysis.