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