week 4 Flashcards
IONISATION:
the process of producing an ion from the analyte (M). Either a radical molecular ion M+● or an adduct ion [M+X]+ (where X = cation).
what does mass spectrometry measures ?
it measures the mass-to-charge ratio (m/z).
MASS SPECTRUM:
a histogram plot with abundance/intensity on the y-axis and mass-to-charge ratio (m/z) on the x-axis.
The Dalton
one twelfth of the rest mass of an unbound atom of 12C in its nuclear and electronic ground state.
Isotopic mass
: calculated from the sum of the most abundant isotopes making up a molecule.
Average mass:
calculated from the average atomic masses of the elements making up a molecule.
Average mass is used when working out amounts of reactants or when calculating yields.
Nominal mass:
calculated from the sum of the most abundant isotopes making up a molecule rounded to the nearest whole number.
Nominal mass is convenient for discussions.
For example “my product has a mass of 126 Da”.
Accurate mass:
experimentally measured mass performed to determine or confirm molecular formulae.
Mass accuracy:
the ‘degree of closeness’ of a measured mass to the theoretical (isotopic) mass.
Mass precision:
the degree to which repeated measurements of mass remain unchanged under the same conditions.
Isobars:
molecules with the same nominal mass, but different formulae and therefore isotopic mass.
how to seperate isobars?
High resolution is required to separate isobaric ions to prevent overlapped peaks from skewing measured masses and reducing mass accuracy.
Mass resolution:
the ability of a mass spectrometer to separate ions that are close in mass.
High resolution is required to…
…determine the accurate mass of an ion. This is to prevent other (isobaric) ions from shifting the measured mass due to detrimental affects on the peak shape.
