Mass spectrometry identity testing

A purity figure tells you how much of a sample is one substance. It does not tell you what that substance is. A vial could be highly pure and still contain the wrong compound entirely. Confirming identity is a separate test, and the standard tool for it is mass spectrometry.

What mass spectrometry measures

Every peptide has a precise molecular weight, determined by its exact sequence of amino acids. Mass spectrometry measures the mass of the molecules in a sample. The instrument converts molecules into charged particles, separates them according to their mass-to-charge ratio, and records what it finds.

For a peptide, the measured mass is compared with the theoretical mass calculated from its known sequence. If they match, the laboratory has good evidence that the sample contains the stated compound. If they do not, the sample is something else.

LC-MS

Mass spectrometry is often combined with liquid chromatography, in a technique called LC-MS. The chromatography step first separates the components of the sample, and the mass spectrometer then identifies them one by one. This makes it possible to identify not only the main compound but also some of the impurities present alongside it.

Identity and purity are different questions

It helps to keep the two tests apart:

• HPLC answers: how much of this sample is the main substance?
• Mass spectrometry answers: is the main substance the one on the label?

A complete picture needs both. A report showing high purity without an identity result tells you the sample is mostly one thing, but not which thing.

Why this matters in the peptide market

Substitution is one of the most common problems with research peptides: a cheaper compound sold as a more expensive one, or a similar-looking peptide sold under a different name. Mass spectrometry is the test that catches it, which is why an identity result is one of the most valuable lines on any peptide report.

What it does not tell you

Mass spectrometry confirms what a compound is. It does not measure how pure the sample is, how much compound the vial contains, or whether the sample is sterile or free of endotoxin. It also cannot always distinguish between molecules with identical mass. For the compounds in our catalog, combining identity testing with HPLC gives a reliable picture of what a sample is and how much of it is the target compound.