Agriculture Reference
In-Depth Information
Table 2.1. Common Parameters of Mass Spectrometers Used in LC-MS
Mass
Analyzer
Type
a
Resolving
Power
(
×
10
3
)
Mass
Accuracy
(ppm)
m
/
z
Range
(Upper
Limit) (
×
10
3
)
Acquisition
Speed
(Spectra/s)
Linear
Dynamic
Range
Price
10
5
-10
6
Quadrupole
3-5
Low
2-3
2-10
Lower
10
4
-10
5
(Linear)
Ion trap
4-20
Low
4-6
2-10
Moderate
10
4
-10
5
Time-of-
flight
10-60
1-5
10-20
10-50
Moderate
5
×
10
3
Orbitrap
100-240
1-3
4
1-5
Higher
Source:
Ref. [49], Table 2, p. 4. Reproduced with permission of Elsevier Science Ltd.
a
TOF and Orbitrap also include common hybrid configurations with quadrupole or linear ion trap as the first
mass analyzer.
analytes. During the data acquisition process, the instrument acquires only the
selected SRM data for the current time segment. Thus, the number of concurrent
transitions is signi
cantly reduced; a higher dwelling time can be applied for
the analytes, which can result in higher sensitivity and more peak points for the
analytes.
High resolution MS such as TOF and Orbitrap MS can be used to analyze virtually
an unlimited number of compounds because they operate in full scan mode and can
reconstruct any desired ion chromatogram using the same full scan data
file [48].
Because accurate mass measurements are almost speci
c and universal for each target
analyte regardless of the instrumentation used, a library search of high-resolution
mass spectra may be performed using the libraries obtained by different mass
spectrometers.
An overview of some common parameters of mass analyzers used in LC
MS is
provided in Table 2.1. The mass resolving power (RP) characterizes the ability of the
mass analyzer to separate two ions of similar
m
/
z
values. RP is de
-
ned as the
m
/
z
value of particular spectral peak divided by the peak FWHM. The older de
nition
based on mass difference between two spectral peaks by a 10% valley is not used in
current LC
-
MS practice. Mass resolution is the inverse of RP expressed in
Δ
m
/
z
for a
particular
m
/
z
(see Eq. 2.1) [11,49].
m
=
z
RP
(2.1)
Δ
m
z
=
Mass accuracy (MA) is the deviation between measured and theoretical (exact)
mass of an ion expressed in parts per million (ppm) (see Eq. 2.2) [11,49]:
m
z
meas
m
z
theor
=
=
10
6
MA
ppm
(2.2)
m
=
z
theor
