Two ions, O+ and NH2+, have the same nominal mass, 16. What resolution is needed to separate them in a mass spectrometer? The masses of the isotopes are N = 14.003070, H = 1.007825, and O = 15.9949 amu.
R = m / D m
m for O+ = 15.9949
M for NH2+ = 14.003070 + 2(1.007825) = 16.01872
D m = 16. 01872 - 15.9949 = 0.02382
R = 16 / 0.02382 = 672 so a resolution of about 700 is needed