Performance of a Hybrid RF/DC Quadrupole-Linear Ion Trap Mass Spectrometer

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Performance of a Hybrid RF/DC Quadrupole-Linear
Ion Trap Mass Spectrometer

• James W. Hager
• MDS SCIEX

ASMS, 2002
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Outline

• Linear ion trap mass spectrometer concept.
• Mass selective axial ion ejection.
• Marriage with triple quad ms.
• Trapping and extraction efficiencies
• Space charge effects
• Performance characteristics.
• Future directions.

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Triple Quad. MS/MS --Tandem in Space

• Only 1 ion pair is stable at any one time.
• Poor scanning efficiency.
• Very efficient for MRM.
• Very selective scans available.

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3D Ion Trap MS/MS --Tandem in Time

• Full mass spectrum for each pulse of ions.
• High scanning efficiency.
• Scanning instrument only.

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Linear Ion Traps

• Ion bottles for optical spectroscopy.
• Minimize fringing fields to maximize performance.
• Ion accumulation for enhanced ms sensitivity.
• Mass analyzers
• RCM, 2002, 16, 512-526.
• JASMS, 2002, 13, 659-669.

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Linear Ion Trap Mass Spectrometer

• Linear Ion Trap Mass Spectrometer
• Ions are trapped by barriers
• Radially RF potential
• Axially DC barriers
• Radial RF determines the ion frequencies of
  motion.
• Radial and axial ejection demonstrated.

Drive RF auxiliary AC
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RF Fringing Fields

• Axial Ion Ejection
• Exit fringing fields couple radial/axial degrees
  of freedom of the trapped ions.
• Excite ions radially to eject them axially.

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Time Averaged Axial Electric Field
Dehmelt approx.
radial amplitude
fringing field
F. Londry, ASMS, 2002 .
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Hybrid Instrument with Q3 Linear Ion Trap MS
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Q3 Trapping Efficiency vs. Chamber Pressure
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Extraction Efficiency vs. Ejection
q-Value (4x10-5 Torr)
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Trapping Extraction Efficiencies

• 5-inch long rod array
• Trapping efficiency 45
• 4x10-5 Torr background pressure
• Extraction efficiency 16-20
• q-value dependent
• Overall efficiency 8

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Hybrid Approach to Product Ion MS/MS

• RF/DC Q1 Q2 Q3
  linear trap

• Advantages
• No time required to isolate the precursor ion.
• No loss for isolation of fragile precursor ions.
• The ion trap is filled with only precursor and
  fragment ions.
• Triple quad. fragmentation patterns.
• No inherent low mass cut-off.

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Product Ion Scanning
N2 CAD Gas
Exit lens
Aux AC
Ion accumulation
Q0
Q1
Q3
Q2
Precursor ion selection
Fragmentation
linear ion trap 3x10-5 Torr

1. Precursor ions selection in Q1.
2. Fragmentation in Q2.
3. Trap products in Q3.
4. Mass scan.
5. Concurrent trapping in Q0.

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Sensitivity Enhancements
QqQ
Reserpine Product Ion
Q1 Open Resolution
Enhanced Product Ion Scan
gt 350x
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Sensitivity EnhancementsReserpine
QqQ
Q1 Open Resolution
Enhanced Product Ion Scan
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No Low Mass Cut-off
Taurocholic Acid Product Ion
LCQ Deca 45 CE 3 amu isolation width
Enhanced Prod Ion Scan 75eV
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Resolution and Scan Speed Reserpine
4000 amu/sec 0.55 amu wide
1000 amu/sec 0.35 amu wide
250 amu/sec 0.15 amu wide
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Mass Shift vs. Ejection q-Value 3.5x10-5 Torr
103X Change of Ion Current
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Mass Shift vs. Input Ion Intensity q0.86,
m/z609
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Space Charge Effects
Q3 Space Charge Effects (3x10-5 Torr)
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RF/DC Quadrupole-Linear Ion Trap Mass Spectrometer

• Ion trap and triple quad capabilities on a single
  platform.
• High sensitivity ion trap scans
• Single MS survey scans
• Product ion scans
• MS3 in Q3
• Triple quad. Functionality
• MRM
• Precursor ion scans
• Neutral loss scans

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Future Directions

• Tandem-in-space ion trap(s) approach allows for
  simultaneous ion processing while the primary
  mass analyzer is scanning.
• Increased sample utililization eff. and thus
  higher duty cycles.
• Very high resolution.

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Acknowledgments

• Yves LeBlanc
• Frank Londry
• Bill Stott
• Bruce Collings
• John Vandermey