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3.16.4 Resolving Power.
At a given mass M, the ratio of M to peak width W:
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:
where:
Then, if W' is the peak width in the same units as those of S',
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Resolving Power =
S'
L = —————— = ————
M1 - M2
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
= mass of peak at which resolution is to be determined
1
M
= mass of a neighboring peak ∆M = M
2
Absolute Resolution
M = M
(see 3.11)
W
M
S'
∆M
– M
1
2
W'
= ———-
(by definition)
L
= M x W/S
b-xi
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