How HPLC works
High-performance liquid chromatography pushes a liquid sample through a column under pressure. Components spend different amounts of time interacting with the column, so they exit at different times. A detector records that exit as a chromatogram.
HPLC is commonly used to evaluate chromatographic purity and to look for impurities the method can detect. The result belongs to the conditions of the run.
What HPLC does not establish
A chromatogram does not, by itself, name the chemical structure. Two different compounds can overlap. The method also does not report properties it was not set up to measure, such as water content or a microbial count.
An educational description of HPLC is not evidence that HPLC was completed for a product. That claim requires a batch record.
How mass spectrometry works
Mass spectrometry converts molecules into charged species and separates those ions by their mass-to-charge ratio. The spectrum can support an identity assignment when the observed mass agrees with the mass expected for the compound.
Fragment ions, when the method produces them, add another check on the structure. Agreement is support. It is still a result of that instrument and that sample.
What mass spectrometry does not establish
A matching mass does not measure every impurity, and it does not describe sterility, stability, or a legal classification. Isobaric compounds, which share a mass, can require a further method to tell them apart.
HPLC and mass spectrometry are often read together: separation from the chromatogram, and a mass that supports identity. Together they still describe only what those two methods measured.