Methods

Mass spectrometry and identity confirmation

2 min read

HPLC answers how much of a sample is one thing. It does not answer what that thing is. That is mass spectrometry's job, and the two questions are genuinely separate.

How it works

The sample is ionised — given an electrical charge — and accelerated through a field that separates ions by their mass-to-charge ratio. Heavier ions deflect less, lighter ones more. The instrument records where each arrives, producing a spectrum of masses present.

For a peptide, the expected molecular weight can be calculated exactly from its amino acid sequence. Sermorelin should weigh 3357.9 g/mol. If the observed mass matches, the molecule in the vial has the composition it should.

Why it catches things HPLC cannot

A chromatogram shows a clean single peak whenever one substance dominates — regardless of which substance that is. A completely different peptide, or the correct sequence with one amino acid substituted, can produce an unremarkable chromatogram at high apparent purity.

A clean peak proves consistency, not identity.

Mass spectrometry catches exactly that. A single wrong amino acid shifts the molecular weight by a measurable amount, and the observed mass no longer matches the theoretical one.

This is why a well-formed certificate reports both, and why purity alone — however high the number — is an incomplete answer.

Research use only. The compounds discussed here are supplied for laboratory research purposes exclusively. They are not drugs, dietary supplements, or cosmetics, and are not intended or approved for human or veterinary use. This article is a summary of published chemistry and pharmacology, provided for reference. It is not guidance for use in any living subject.