5. Mass Analyzers: Quadrupole ion trap?  

6. “Ideal” Geometry Quadrupole Trap
Theoretical
“infinite”
hyperbolic
electrodes
Actual
physical
electrodes

7. Mass Analyzers: ION TRAPS
Three-dimensional quadrupole field
Wolfgang Paul Nobel Prize1989
MSn capability.

19. Generating Fields in an Ion TrapRF
Generator V t

20. Trapping Ions RF
Generator
Range of masses trapped depends upon amplitude of rf voltage V t
Sugar Salt Cocaine

21. Trapping Ions RF
Generator V t
Increasing the rf amplitude means lower mass ions are not trapped

22. Theory - Mathieu Stability Diagram
= 0
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
0.1
0.3 a z q
not trapped
trapped
proportional to frequency of ion motion in z direction
Add 0.91

23. Trapping a range of ions
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
0.1
0.3 a z q
V= 600 volts

24. Trapping a range of ions
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
0.1
0.3 a z q
V= 1000 volts
V= 600 volts

25. Ion Trap as a Mass SpectrometerRF
Generator
White powder analysis
signal 56 57 58 59
mass
Detector

26. Ion Trap as a Mass SpectrometerRF
Generator
White powder analysis
signal 56 57 58 59
mass
Detector

27. Ion Trap as a Mass SpectrometerRF
Generator
Eject mass 58
White powder analysis
signal 56 57 58 59
mass
Detector

28. Ion Trap as a Mass SpectrometerRF
Generator
White powder analysis
signal 56 57 58 59
mass
Detector

29. Mass-selective instabilityRF
Generator
signal 50
100
150
200
mass

30. Resonance Ejection RF
Generator
Change the electric field by applying supplemental ac voltage across end cap electrodes V t

31. Ion Motion in Resonance Ejection
without supplemental ac end cap voltage
with
supplemental ac
end cap voltage
z=z0
Push
Define z somehow
Apply supplemental ac voltage to end caps
-z=z0

33. Resonance Ejection a q Any ion in the ion trap can be ejected
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
0.1
0.3 a z q
Any ion in the ion trap can be ejected
Frequency of ac voltage applied to end caps
Change ion positions

34. Tandem MS in Ion Trap
Trap a selected ion

35. Mass Analyzers: ION TRAPS
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

36. 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