The new instrument consists of a three-dimensional RF quadrupole ion trap (QIT), a linear RF quadrupole collision cell (q), and an orthogonal, reflectron time-of-flight mass spectrometer (TOF) configured in a tandem-in-space arrangement (QITqTOF).

The QITqTOF configuration enables MS/MS spectra of multiple types of parent ions, arbitrarily selected from a heterogenous population, to be obtained from a single ion accumulation event in the QIT.

Features of the new tandem-in-time and -in-space instrument include high throughput, enhanced duty cycle, and flexibility.

Prof. Hermann Wollnik for the generous gift of the orthogonal, reflectron time-of-flight mass spectrometer and for valuable discussions regarding its operation

Prof. Scott McLuckey (Purdue Univ.) for advice in initial instrument design considerations and assistance in making the TOF operational

Dr. Scott Quarmby and Dr. Brody Guckenberger (Thermo Finnigan) for helpful information and advice regarding operation and modification of the PolarisQ electronics

Research sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LLC for the U. S. Department of Energy under Contract No. DE-AC05-00OR22725

1. I.V. Chernushevich, A.V. Loboda, B.A. Thomson, “An Introduction to Quadrupole-Time-of-Flight Mass Spectrometry” J. Mass Spectrom. 36, 849-865 (2001).

2. M.G. Qian, D.M. Lubman, “Procedures for Tandem Mass Spectrometry on an Ion Trap Storage/Reflectron Time-of-Flight Mass Spectrometer” Rapid Commun. Mass Spectrom. 10, 1911-1920 (1996).

3. J.M. Campbell, B.A. Collings, D.J Douglas, “A New Linear Ion Trap Time-of-Flight System with Tandem Mass Spectrometry Capabilities” Rapid Commun. Mass Spectrom. 12, 1463-1474 (1998).

4. C.S. Hoaglund-Hyzer, D.E. Clemmer, “Ion Trap/Ion Mobility/Quadrupole/Time-of-Flight Mass Spectrometry for Peptide Mixture Analysis” Anal. Chem. 73, 177-184 (2001).

5. A.F. Dodonov, V.I. Kozlovski, I.V. Soulimenkov, V.V. Raznikov, A.V. Loboda, Z. Zhen, T. Horwath, H. Wollnik, “High-Resolution Electrospray Ionization Orthogonal-Injection Time-of-Flight Mass Spectrometer” Eur. J. Mass Spectrom. 6, 481-490 (2000).

6. A Loboda, A. Krutchinsky, O. Loboda, J. McNabb, V. Spicer, W. Ens, K. Standing, “Novel Linac II Electrode Geometry for Creating an Axial Field in a Multipole Ion Guide” Eur. J. Mass Spectrom. 6, 531-536 (2000).

Triple quadrupole (QqQ) and three dimensional quadrupole ion trap (QIT) instruments are widely used for tandem mass spectrometry. Because the QqQ is normally operated so that parent ion selection in Q1, parent ion dissociation in q, and product ion mass analysis in Q3 occur sequentially in space as ions traverse the instrument, the MS/MS process is known as tandem-in-space. In constrast, MS/MS in a quadrupole ion trap is often referred to as tandem-in-time since selective parent ion dissociation and subsequent product ion mass analysis can be performed within the same volume.

One limitation of triple quadrupole instruments and quadrupole ion trap instruments as used for MS/MS is that acquisition of a product ion mass spectrum can be time consuming because the mass analyzer (Q3 or the QIT itself) must scan through many mass-to-charge ratio values to record a complete spectrum. In addition, in the triple quadruple instrument, all other product ions outside of the transmission window are lost. Furthermore, when a triple quadrupole instrument or quadrupole ion trap instrument is performing an MS/MS analysis on parent ions having a specific mass-to-charge ratio value, additional parent ions at different mass-to-charge ratio values cannot be introduced. Thus, during the product ion mass analysis time, ions produced by the ion source may be wasted, resulting in a very low duty cycle and poor overall sensitivity for the system.

To overcome such limitations, recent instrument development has focused on tandem mass spectrometry with hybrid multipole/time-of-flight instruments. One such instrument is the quadrupole time-of-flight mass spectrometer1 (QqTOF), in which the third quadrupole of a QqQ is replaced by a TOF. The advantage of the TOF is that it can record 10,000 or more complete mass spectra in one second without scanning. Thus, product ion mass spectra can be acquired more quickly, and the duty cycle is greatly improved. Product ion mass resolution and accuracy are generally improved as well. However, as with the triple quadrupole ion instruments, parent ions at different mass-to-charge ratio values cannot be introduced during MS/MS analysis.

Quadrupole2 and linear3 ion traps have also been used in such hybrid instruments (QITTOF, QlinearTOF). Parent ion selection by mass-to-charge ratio and dissociation initially occur in the ion trap, and the product ions are then pulsed into the TOF for mass analysis. The disadvantage of TOF for rapid acquisition of mass spectra is somewhat negated however, because the quadrupole ion trap is only capable of selecting and dissociating parent ions at rates that are a couple orders of magnitude lower than TOF mass analysis. Another technique separates ions in time via ion mobility spectrometry (IMS) prior to MS/MS analysis with a QqTOF4. The duty cycle is improved by storing a population of ions in a QIT prior to separation in the IMS. The IMSQqTOF, unlike most MS/MS instruments however, is unable to arbitrarily control parent ion selection and spacing in time.

We describe a new hybrid mass spectrometer that is comprised of standard components: a three-dimensional quadrupole ion trap, a linear quadrupole, and a time-of-flight mass spectrometer. The physical arrangement of components, combined with the associated unique method of operation, allows for generation of MS/MS spectra on multiple packets of parent ions selected arbitrarily from a heterogeneous ion population collected in a single accumulation event. Thus, the instrument promises to provide significant enhancement in the overall throughput for MS/MS, while retaining the advantages and overcoming the limitations of current hybrid mass spectrometers in such applications.

Figure 1 shows a schematic representation of the QITqTOF instrument:

A three-dimensional RF quadrupole ion trap (QIT), linear RF quadrupole (q), and time-of-flight (TOF) mass spectrometer are arranged in a tandem configuration (QITqTOF)

The QIT serves to accumulate and sort ions by m/z

The q functions as a collision cell and ion guide

The TOF mass analyzes product ions from CID in q

Figure 3 is a more detailed drawing of the tandem arrangement for the three-dimensional RF quadrupole iontrap (QIT), linear RF quadrupole (q), and orthogonal,reflectron time-of-flight mass spectrometer (TOF).

1. The QIT is a modified Finnigan PolarisQ:

The ring electrode, endcaps, and turbomolecular pump (250 L-s-1) were moved from the vacuum housing of the PolarisQ to a 6-inch vacuum cube

3-element ion lenses were mounted at the entrance and exit of the QIT

A simple ORNL-designed ES ion source was mounted on the cube

The PolarisQ electronics and software were used to drive the ring electrode and endcaps of the QIT

2. A high-resolution, electrospray ionization, orthogonal injection reflectron TOF5 was interfaced to the QIT:

The ES ion source was removed and replaced by a custom-designed QIT interface

A variable potential entrance aperture plate, collision gas inlet, and pressure monitor were added to q, which is a Linac II geometry6 linear quadrupole that creates an axial field in the device

Extrel C-50 quadrupole electronics were used to drive q

A QIT start-of-scan synchronization pulse triggers a delay generator which gates the TOF

The MCP output is currently sent to a digital oscilloscope for data acquisition

3. The plot above the instrument drawing gives approximate potentials for various regions

The QIT is lowered in potential because ions are ejected with several hundred eV of kinetic energy

The 3-element immersion lens at the QIT exit focuses and adjusts the ion kinetic energy to be compatible with the q and the TOF

The potentials on q and its entrance and exit apertures determine the CID collision energy

The DC quadrupole and one-dimensional Einzel lens focus and steer the ion beam before it enters the TOF acceleration region

The TOF acceleration region is held at ground potential until the product ion packet enters

Product ions are gated into the TOF via “push” and “pull” grids that are pulsed to ±1kV

Ions are accelerated to 5 keV in the field-free region of the TOF

The ion beam is focused during transit through the TOF via a two-stage reflectron

Features of the QITqTOF configuration and its proposed operational mode for tandem mass spectrometry:

MS/MS spectra can be obtained for all parent ions in a heterogenous trapped ion population without multiple accumulation/dissociation cycles

Arbitrary parent ion selection and MS/MS sequence

Flexible parent ion dissociation conditions

Faster MS/MS data acquisition and enhanced duty cycle compared with QIT, QITlinear , QqQ, QqQlinear instruments

Enhanced product ion mass resolution and accuracy compared with QqQ, QIT, QITlinear instruments

Parent IonEject

EntranceGate

Open

Close

TOF

QIT

Time

m/z

Close

OpenEntranceGate

mTime

TOFTime

CIDTime

Par

ent

Ion

M

Figure 2

CONCLUSIONS

ACKNOWLEDGMENTS

REFERENCES

A New Tandem-in-Time and –in-Space Mass Spectrometer for High-Throughput MS/MSD.E. Goeringer, A.R. Warren, M.B. Wise, K.J. Hart

Organic & Biological Mass Spectrometry Group, Chemical Sciences DivisionOak Ridge National Laboratory, Oak Ridge, TN 37831-6131

-5 kVAccel.

1.5 kVReflector

-200 VQIT

0 V

-1 kVPull

1 kVPush

15 VOut

18 VQuad

25 VIn

150 VFocus

-350 VInter. Grid

2 mm Dia.

5 mm Dia.

3 mm Dia.

RF Quad Collision Cell

1 mTorr

Chamber 1 Torr

350 L/s

250 L/s

Ion Trap 0.5 mTorr

DC Quad

ChanneltronQIT Detector

350 L/s

QIT0.5 mTorr

RF QuadrupoleCollision Cell

5 mTorr

350 L/s

250 L/s

o-RTOF10-6 Torr

0 V

0 V

Field-FreeRegion

Two-StageReflector

MCPTOF DetectorDC Quad

PolarisQ

INTRODUCTION

QITqTOF

Mass-Selective IonStorage/Sorting

Parent IonDissociation

Product IonMass Analysis

Three-DimensionalQuadrupole

Ion Trap

QuadrupoleCollision Cell

o-RTOF

ESSource

Figure 1

Figure 2 shows a timing diagram for one mode of tandem-in-time and -in-space MS/MS operation of the QITqTOF instrument:

1. A heterogenous population of (parent) ions from the ES source is collected in the QIT

2. A mass-selected packet of parent ions is ejected from the QIT into the q

3. The packet of parent ions undergoes CID during transit through the q

4. TOF operation is synchronized with arrival of the product ion packet in the acceleration region

5. Product ion mass analysis occurs in the TOF

6. Repeating steps 2-5 enables MS/MS analysis of all parent ions initially stored in the QIT without reloading

OVERVIEW

Figure 3: Drawing of the prototype QITqTOF and plot of the potentials in various regions of the instrument

CONCEPTUAL DESIGN EXPERIMENTAL