Observed mass

Definition

The molecular mass recovered from a sample spectrum, reported alongside the theoretical mass and the difference between them.

Certificates from this laboratory do not carry an observed mass, because identity here is confirmed against reference spectra rather than by mass measurement. An observed mass on a report is a mass-spectrometric result from whoever produced it.

Related terms

Theoretical mass

The molecular mass calculated for the expected compound from reference data, on a stated basis, usually the free base rather than the salt.

Mass accuracy

How close a measured mass is to the true mass, usually expressed in parts per million.

Reference spectrum

A spectrum recorded from material of known identity, which a sample spectrum is compared against.

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 ionisationMass-to-charge ratioCharge stateDeconvolutionIsotope patternIon suppressionIsobaricStereoisomerRetro-inverso peptide

Read more

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