Tools

Mass accuracy — ppm error checker

Observed against theoretical monoisotopic mass, in parts per million, with the threshold that matters for an identity claim.

An identity confirmation on a certificate rests on mass spectrometry: the observed mass against the theoretical one. The difference is conventionally expressed in parts per million, because absolute difference means nothing without the size of the molecule.

A modern high-resolution instrument should land within a few ppm. A figure of tens of ppm on a peptide of this size is not a rounding artefact — it is either a different molecule, a different charge state, or an instrument that was not calibrated.

Theoretical mass (Da)monoisotopic, from the sequence

Observed mass (Da)as reported on the certificate

Tolerance (ppm)10 is a common acceptance limit

—Mass error

What a good number does not prove

Mass tells you the molecule weighs what it should. It does not distinguish isomers, it says nothing about purity, and it says nothing about how much peptide is in the vial. Identity, purity and content are three separate measurements and a certificate that reports one is not reporting the others.

Maintained by the wiki editors. It runs entirely in your browser — nothing is sent anywhere — and it shows its working so you can check it by hand. Do it by hand the first few times. Nothing here is medical advice; see the disclaimer.

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