performance of a hybrid rf/dc quadrupole-linear ion trap mass spectrometer james w. hager mds sciex...
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Performance of a Hybrid RF/DC Quadrupole-Linear Ion
Trap Mass Spectrometer
James W. Hager
MDS SCIEX
ASMS, 2002
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.
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.
Q0 Q1 Q2 Q3
3D Ion Trap MS/MS --Tandem in Time
• Full mass spectrum for each pulse of ions.• High scanning efficiency.• Scanning instrument only.
• “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.
Linear Ion Traps
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
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.
Time Averaged Axial Electric Field
fringing field radial amplitude
F. Londry, ASMS, 2002 .
Dehmelt approx.: xXx
2222
RFquad z, 8YXq
e
mΩ
z
fE x
Hybrid Instrument with Q3 Linear Ion Trap MS
N2 CAD Gas
linear ion trap3x10-5 Torr
Aux AC
IQ2 IQ3 Exit
Skimmer
Orifice
LINAC
IQ1
Q0 Q1 Q2 Q3
0
10
20
30
40
50
60
70
80
90
100
0.0E+00 2.5E-04 5.0E-04 7.5E-04
Pressure (Torr)
Eff
icie
ncy
(%
)
Trapping Eff (No LINAC)
Trapping Eff (LINAC)
Q3 Trapping Efficiency vs. Chamber Pressure
Extraction Efficiency vs. Ejection q-Value(4x10-5 Torr)
0
5
10
15
20
25
0.25 0.35 0.45 0.55 0.65 0.75 0.85
Ejection q-Value
Ex
tra
cti
on
Eff
icie
nc
y (
%)
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%
Hybrid Approach to Product Ion MS/MS
• RF/DC Q1 Q2 Q3 linear trapfrags.eV
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.
Product Ion Scanning
1. Precursor ions selection in Q1.2. Fragmentation in Q2.3. Trap products in Q3.4. Mass scan.5. Concurrent trapping in Q0.
Q1 Q3Q0
N2 CAD Gas
Q2
linear ion trap3x10-5 Torr
Precursor ion selection
Ion accumulation
Fragmentation
Exit lensAux AC
Enhanced Product Ion Scan
Q1 Open Resolution
Reserpine – Product Ion QqQ
> 350x
Sensitivity Enhancements
Taurocholic Acid–
Product Ion
LCQ Deca – 45% CE
3 amu isolation width
Enhanced Prod Ion Scan – 75eV
No Low Mass Cut-off
1000 amu/sec~0.35 amu wide
4000 amu/sec~0.55 amu wide
250 amu/sec~0.15 amu wide
Resolution and Scan Speed: Reserpine
Mass Shift vs. Ejection q-Value3.5x10-5 Torr
103X Change of Ion Current
0.000
0.025
0.050
0.075
0.100
0.45 0.55 0.65 0.75 0.85 0.95
Ejection q-Value
Ob
serv
ed
Ma
ss S
hift
(a
mu
)
Mass Shift vs. Input Ion Intensityq=0.86, m/z=609
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
1.0E+04 1.0E+05 1.0E+06 1.0E+07 1.0E+08 1.0E+09
Ion Intensity (cps)
Mas
s S
hif
t (a
mu
)
Space Charge Effects
1.91e2 cps
602 604 606 608 610 612 614 616 618
2.26e6 cps
602 604 606 608 610 612 614 616 618m/z
=0.02 Th
(a)
(b)
104x > ion current
0.02 amu
Q3 Space Charge Effects (3x10-5 Torr):
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
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.