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

Q1 Open Resolution

Enhanced Product Ion Scan

QqQ

Sensitivity Enhancements—Reserpine

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.

Acknowledgments

• Yves LeBlanc

• Frank Londry

• Bill Stott

• Bruce Collings

• John Vandermey