Mass-to-charge ratio

Definition

The quantity a mass analyser actually sorts on, written m/z. It is the ion mass divided by its number of charges, which is why a molecule carrying three protons appears at roughly a third of the position of the same molecule carrying one.

Related terms

Charge state

The number of charges an ion carries, written as [M+nH]ⁿ⁺ for a peptide that has picked up n protons.

Deconvolution

The calculation that recovers a single molecular mass from a series of charge states.

About mass spectrometry

Terms a reader meets on mass-spectrometric reports from other laboratories, and on confirmatory work sent out. This laboratory has no in-house mass spectrometer, and its certificates carry no mass spectrum.

Electrospray ionisationObserved massTheoretical massMass accuracyIsotope patternIon suppressionIsobaricStereoisomerRetro-inverso peptide

Read more

• Purity versus identity
• Peptide identity testing
• The full peptide testing glossary