Mass Analyzers: Quadrupole ion trap?
“Ideal” Geometry Quadrupole Trap
Theoretical“infinite”hyperbolicelectrodes
Actualphysical
electrodes
Mass Analyzers: ION TRAPS
•Three-dimensional quadrupole field
•Wolfgang Paul Nobel Prize1989
•MSn capability.
V t
Generating Fields in an Ion Trap
RF Generator
RF Generator
V t
Trapping Ions
Range of masses trapped depends upon amplitude of rf voltage
Sugar Salt Cocaine
RF Generator
V t
Trapping Ions
Increasing the rf amplitude means lower mass ions are not trapped
220
20 )2(
8
zrm
eVqz
Theory - Mathieu Stability Diagram
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3a
z
qz
220
20 )2(
16
zrm
eUaz
not trapped
= 0
trapped
proportional to frequency of ion motion in z direction
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3a
z
qz
220
20 )2(
8
zrm
eVqz
Trapping a range of ions
V= 600 volts
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3a
z
qz
220
20 )2(
8
zrm
eVqz
Trapping a range of ions
V= 600 voltsV= 1000 volts
RF Generator
Ion Trap as a Mass Spectrometer
Detectorsi
gnal
56 57 58 59mass
RF Generator
Ion Trap as a Mass Spectrometer
Detectorsi
gnal
56 57 58 59mass
RF Generator
Ion Trap as a Mass Spectrometer
Detectorsi
gnal
56 57 58 59mass
Eject mass 58
RF Generator
Ion Trap as a Mass Spectrometer
Detectorsi
gnal
56 57 58 59mass
RF Generator
Vt
Mass-selective instability
sign
al50 100 150 200
mass
RF Generator
Resonance Ejection
V t
Change the electric field by applying supplemental ac voltage across end cap electrodes
without supplemental ac end cap voltage
withsupplemental acend cap voltage
Ion Motion in Resonance Ejection
z=z0
-z=z0
Apply supplemental ac voltage to end caps
Resonance Ejection
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0.0
0.1
0.2
0.3a
z
qz
Any ion in the ion trap can be ejected
Frequency of ac voltage applied to end caps
Tandem MS in Ion Trap
Trap a selected ion
Benefits•High sensitivity •Multi-stage mass spectrometry •Compact mass analyzer
Limitations•Poor quantitation •Very poor dynamic range (can sometimes be compensated for by using automatic gain control) •Subject to space charge effects and ion molecule reactions •Collision energy not well-defined in CID MS/MS •Many parameters (excitation, trapping, detection conditions) comprise the experiment sequence that defines the quality of the mass spectrum
Applications•Benchtop GC/MS, LC/MS and MS/MS systems •Target compound screening •Ion chemistry
Mass Analyzers: ION TRAPS
1 INJECTION.exe
2 ISOLATION.exe
3 PARENT STABILIZATION.exe
4 EXCITATION.exe
5 DAUGHTER EJECTION.exe
6 DETECTION.exe
ION TRAPS : Time related issues MS/MS/MS
A: ionization
B: trapping
C: protonation
D: selection of parent ion
E: stabilization
F: CID
G: selection of daughter
H: stabilization +CID
I: Scanning of grand-daughter ions and tetection
Top Related