The highest resolution mass spectra are obtained by Fourier transform ion cyclotron resonance mass spectrometry. Molecular ions of two peptides (chains of seven amino acids) differing in mass by 0.000 45 Da were separated with a 10% valley between them. The ions each have a mass of 906.49 Da and a width at half-height of 0.000 27 Da. Compute the resolving power by the 10% valley formula and by the half-width formula, both in Equation 21-1. Compare the difference in mass of these two compounds with the mass of an electron.

Equation 21-1

m m Resolving power or (21-1) Am