Mass Spectrometric Methods, Overview and Figures of Merit

MS

Mass Spectrometry

Mass Spectrum

signal intensity vs m/z

signal intensity

reflects the abundance of a given species and its ionization efficiency; units often mV or V, counts, or arbitrary units

Relative intensity

% in reference to the most abundant (base peak)

m/z

mass to charge ratio, dimensionless; mass as u = 1/12^th the mass of ¹²C, mass in Daltons, or mass in Thompson units

1 u = 1 Da = 1.661*10^-27 kg

1 Th = 1 u/e ~= 1.036*10^-8 kg/C

Total charge given by ions (equation)

q = ze

e = electron charge = 1.6*10^-19 C

z = number of charges

Molecular ion

intact ionized form of the analyte produced by gain or loss of one electron; M^+• or M^-•

Nitrogen Rule

for organic compounds, molecular ions of odd nominal m/z possess an odd number of nitrogen atoms, even nominal m/z-even nitrogen atoms

Cations

Anions

Vacuum

Boltzmann Equation

Average Mass

Nominal Mass

Monoisotopic Mass

Mass defects

variations in isotopic abundances

Figures of Merit, listed

Resolving power, resolution, mass accuracy, mass range, range/linear dynamic range, abundance sensitivity, precision, efficiency, sped, compatibility with ionizer, practical considerations

FOM, Resolving power

FOM, Resolution

FOM, mass accuracy

FOM, mass range

FOM, mass range

FOM, range/linear dynamic range

FOM, abundance sensitivity

FOM, precision

FOM, efficiency

FOM, speed

FOM, compatibility with ionizer

FOM, practical considerations