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3.16.4 Resolving Power.
At a given mass M, the ratio of M to peak width W:
Resolving Power =
M = M (see 3.11)
W M
4 Discussion of Resolution
4.1 MASS SCALE
Some mass spectrometers produce a graphical scan having an abscissa
which is not linear in mass number. It then becomes necessary, for the
calculation of resolution, to convert the abscissa to a linear mass scale. To
do this, it is assumed that, for a sufficiently small range of mass numbers,
the abscissa is actually linear in mass number. To convert from the
abscissa scale to mass units, the following formula is used:
S’ S’
L = —————— = ————
M1 - M2 ∆M
where:
S = peak separation in any convenient units (centimeters, volts,
cycles per second, etc.)
L = the number of units, of the kind chosen for S, equivalent
to 1 mass unit
M
1
= mass of peak at which resolution is to be determined
M
2
= mass of a neighboring peak ∆M = M
1
– M
2
Then, if W’ is the peak width in the same units as those of S’,
W’
Absolute Resolution = ———- (by definition)
L
= M x W/S
1109-186-00 Rev. C b-xi
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