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Resolution and mass measurement accuracy are two fundamental concepts in TOF mass spectrometry that must be understood to fully utilize the experiment. Resolution is the experimental observable of the resolving power of the instrument. Resolving power is the ability to separate components that are similar within the separating medium. In TOF mass spectrometry, the resolving power of the instrument is the ability to separate ions of similar flight times into separate signals.
The resolution observed in TOF mass spectrometry is calculated from the signals observed and is derived from the relationship between m/z and flight time. The m/z is related to flight time by Equation 1, where m is mass, D is distance, and t is time.
m = (2eV / d2) * t2 [Eq. 1]
The derivative of Equation 1 yields:
dm = (2eV / d2) * 2t dt [Eq. 2]
The relationship of m / dm yields:
m / dm = t / 2dt [Eq. 3]
Alternatively, Equation 3 can be written as follows:
m / Dm = t / 2Dt [Eq. 4]
where Dt is equal to the full width at half maximum (FWHM) of the peak measured.
Equation 4 is the definition of resolution for TOF mass spectrometry and is calculate from the FWHM of a peak along with the respective centroid in time or m/z.
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