1. CH 908: Mass Spectrometry Lecture 6 Mass Analyzers Prof. Peter B. O’Connor

2. Objectives Types of mass spectrometers and how they operate –Time-of-flight –Quadrupoles –Ion traps Mathieu stability diagram analyss –FTICR –Orbitrap

3. Electron Multiplier

4. Notes: channeltron microchannel plates chevron

5. Mass Spectrometers Time of Flight Magnetic Sector Quadrupole Triple Quadrupole Quadrupole Ion Trap FTICRMS Orbitrap Mass Spectrometers DO NOT measure mass. They measure mass/charge ratio. Understanding how mass spectrometers work is understanding how ions move in electric and magnetic fields.

6. Ions in a DC Electric Field F = qE = m d 2 x/dt 2 + 10 KV

7. Time of Flight Mass Spectrometry MALDI-TOF EI-TOF ESI-TOF The most simple of all mass spectrometers, at least conceptually. Linear versus reflectron Delayed extraction (time lag focusing) Detection electronics PSD scan Orthogonal injection

8. Basic TOF mass spectrometer

9. Laser V D (field free drift region) Source S Oscilloscope + + + + Figure 3. The principle of MALDI time-of-flight mass spectrometry. 1.TOF requires a pulsed ion source 2.TOF requires a small kinetic energy distribution in the ions 3.Radial dispersion causes signal loss 4.TOF requires a detector/oscilloscope/digitizer that’s MUCH faster than the ion flight time.

10. TOF fundamental limitations Resolution limited by: length of TOF flight tube kinetic energy distribution - delayed extraction - reflectron - orthogonal injection propagation delay in detector

11. Laser VsVs D 1 (first field free drift region) Source S Oscilloscope + + Figure 4. Combined Linear/Reflectron MALDI time-of-flight mass spectrometer. D 2 (second field free drift region) First Detector Second Detector V r ≈ V s deflector + + + +

12. Figure 14. Quadrupole Time-of-Flight Hybrid V r ≈ V p Laser V D (field free drift region) Source S Oscilloscope + + + Pusher (V p ) + + Delay Generator Q0Q0 Q1Q1 Q2Q2 (RF-only)(mass filter)(RF-only) + + Focusing + + + + + + + + Collision Cell + + +

13. second field free drift region first field free drift region Figure 6. MALDI tandem time-of-flight mass spectrometer. Laser VsVs Source Oscilloscope + + Detector V r ≈ V s deflector + + + + + + + + + + + Collision Cell (V c ) Delay Generator

14. TOF Parameters Simple, cheap (in theory), robust, sensitive. A good modern TOF should give:  >10k Resolving power  ~1-10 fmol sensitivity (single scan)  ~10 ppm mass accuracy internally calibrated (5 ppm if the peak is particularly large or clean).  >1000 scans/second  Unlimited mass range TOFMS Calibration Equation m = At 2 +B

15. TOF fundamental limitations Resolution limited by: length of TOF flight tube kinetic energy distribution propagation delay in detector Sensitivity limited by: ion stability ion transfer efficiency MS/MS is difficult

16. Ions in a Magnetic Field F=qv x B + BB V F

17. Magnetic Sector Mass Spectrometry MALDI EI ESI Large, expensive, obsolete. Swept beam instrument The first “High Resolution” mass spectrometer (> 10k RP) Lousy sensitivity (~1 nmol) High energy collisional fragmentation Extremely linear detector response (isotope ratio mass spectrometry) Sector Calibration Equation m = AB 0 2 r 2 /V Jeol and Thermo-Finnigan MAT

18. Ions in a magnetic field

19. Sector Fundamental Limitations Resolution/sensitivity tradeoff by using a mass filtering slit Resolution limited by: magnetic/electric field homogeneities slit width Sensitivity limited by: ion transfer efficiency slit width metastable decay Scan speed / scan stability tradeoff

20. Quadrupoles MALDI EI ESI Small, cheap, ubiquitous. Swept beam instrument Resolution typically 1000, mass accuracy typically 0.1% Sensitivity depends on the source. Typically in the 100 fmol range.

21. 1989 Nobel Prize in Physics for development of ion trapping techniques Wolfgang Paul (quadrupole ion traps) Hans Dehmelt (Penning ion traps)

22. Quadrupole mass spectrometer

23. Wiring of a quadrupole

24. The potential energy diagram of a quadrupole showing the saddlepoint in the electric field (generated using Simion 7.0)

25. 3D - Quadrupole ion traps linear ion traps 3D ion traps They follow exactly the same rules as quadrupoles

26. Figure 11. The shape of Paul ion trap mass spectrometers. r z A. a cross-section of a hyperbolic quadrupole ion trap B. a potential energy diagram of the QIT showing the saddlepoint in the electric field (generated using Simion 7.0)

27. Quadrupole Ion Traps Capillary Skimmer Lenses Octopole Ion Guide Lenses Entrance Endcap Ring Electrode Exit Endcap

28. Quadrupoles q z  V/m q z  f ion a z  U/m z stability r stability 0.5 1.01.5 qzqz Operating Line  =1.0 q z =.908 Stable z & r azaz 0.2 0.0 -0.2 -0.4 -0.6 0.4 + + + - - “Matthieu eqn” A ± = U ± Vsin( ωt)

29. Quadrupole Ion Traps q z  V/m q z  f ion a z  U/m z stability r stability 0.5 1.01.5 qzqz Operating Line  =1.0 q z =.908 Stable z & r azaz 0.2 0.0 -0.2 -0.4 -0.6 0.4 + + + - - “Matthieu eqn” A ± = U ± Vsin( ωt)

30. Figure 12. Mathieu stability diagram with four stability points marked. Typical corresponding ion trajectories are shown on the right. 0.5 1.0 qzqz azaz 0.2 0.0 -0.2 -0.4 -0.6 0.0 z stable r stable r and z stable q z = 0.908 A A B C D B C D a z = 0.02, q z = 0.7a z = 0.05, q z = 0.1 a z = -0.2, q z = 0.2a z = -0.04, q z = 0.2

31. QITMS: Mass-Instability Ion Ejection 0.5 1.01.5 qzqz Operating Line  =1.0 q z =.908 azaz 0.2 0.0 -0.2 -0.4 -0.6 0.4 + + + - - High m/z Low m/z Mass Analysis: Ramp RF Volt. on ring electrode Ions increase in q z value Ions become axially unstable at q z = 0.908 Ions are ejected from ion trap Low m/z ions are detected first

32. QITMS: Resonant Ejection Mass Analysis: Ramp RF Volt. on ring electrode As RF increases ions increase in q z Apply dipolar AC signal to endcap electrodes for resonant ejection Ions are ejected radially from trap Low m/z ions are detected first 0.5 1.01.5 qzqz Operating Line  =1.0 q z =.908 azaz 0.2 0.0 -0.2 -0.4 -0.6 0.4 + + + - - High m/z Low m/z Res. Ejection at  z =2/3

34. QITMS Parameters MALDI EI ESI Small, cheap, ubiquitous. Ion trap instrument Resolution typically 1000, mass accuracy typically 0.1% Sensitivity depends on the source. Typically in the 100 fmol range. MS n compatible Operates in 10 -4 mbar Helium. Ion Molecule Reactions (e.g. gas phase H/D Exchange) Why is this problematic? QITMS Calibration Equation m = AV/r 2 f 2

35. Quadrupole MS Fundamental Limitations Resolution: homogeneity of the electric field (charging of the electrodes, or inaccurate machining distorts this) scan speed Sensitivity: scan speed ion transfer efficiency Mass range: limited on high end by size of trap and potentials available limited on low end by stability diagram

36. Octopole ion guide/trap

38. Hexapole ion trap

39. Fourier Transform Mass Spectrometer MALDI EI ESI Big, expensive, but superior performance. Ion trap instrument Resolution typically >50000 broadband, >1,000,000 narrowband Mass accuracy typically 1 ppm internally calibrated 5-10 ppm externally calibrated Sensitivity depends on the source. Typically in the 100 fmol range. MS n compatible Ion Molecule Reactions (e.g. gas phase H/D Exchange)

40. Electrospray FTMS Actively Shielded 7T Superconducting Electromagnet Turbo pump Electrospray Ion Source RF-only Quadrupole Ion Guide Cylindrical Penning Trap How Does FTMS Work?

41. V qtrap V ftrap V inner-rings OR SK Q0 IQ1 ST Q1 IQ2 Q2 IQ3 GR Gate Valve (ground) Shutter RNG RF-Only Hexapole ESI qQq-FTMS Diagram

42. How Does FTMS Work? The Penning Trap The ions’ view of the cell

43. How Does FTMS Work? + - Ions are trapped and oscillate with low, incoherent, thermal amplitude Excitation sweeps resonant ions into a large, coherent cyclotron orbit Preamplifier and digitizer pick up the induced potentials on the cell.

44. How Does FTMS Work? 6008001000120014001600 m/z RF Sweep Transient Image current detection Mass Spectrum FFT 10 MHz 10 kHz RP ≅ ft/2 Sensitivity  ft Calibrate High Resolution (~50,000 FWHM) High mass accuracy (~1 ppm) High sensitivity (femtomoles)

45. Good FTICR review article

46. Effect of transient duration

47. 7008009001000110012001300 1400 1500 700800900100011001200130014001500 10801090 1100 7008009001000110012001300140015001600 [M+2H] 2+ Beta Casein Tryptic digest, 2 pmol/ul T 15 y7y7 * y8y8 y9y9 y 10 y 11 X X X X X y 12 y 13 y 14 b7b7 b8b8 * b9b9 b 10 b 11 * * * b 12 Y 13 2+ ? 1+ MS Isolation MS/MS

48. FTMS Calibration Equation Theory: ω ± = ω c /2 ± (ω c 2 /4 – 2eVα/ma 2 ) 1/2 Practice: m = A/f + B/f 2 + C m = A/(f-B-CV-DI) ω c = qB 0 /m 1. Zhang, L. K.; Rempel, D.; Pramanik, B. N.; Gross, M. L. Accurate mass measurements by fourier transform mass spectrometry Mass Spectrom Rev 2005, 24, 286-309.

49. FTMS Fundamental Limiting Factors Resolution Pressure Magnetic field (strength and homogeneity) Electric field (homogeneity) Space charge Sensitivity Preamplifier Noise Magnetic field strength Space charge Mass range Magnetic field Frequency performance of electronics

50. A new instrument – the orbitrap

51. Self Assessment In TOF-MS, which ions arrive at the detector first? Why? In a QIT, what q-value corresponds to the low m/z cutoff in RF-only mode? What part of the Mathieu stability diagram is used in mass filtering mode in a quadrupole or QIT? In FTICR, doubling the detection time will result in what change to the resolving power? Doubling the magnetic field will result in what change?

52. Fini… CH908: Mass spectrometry Lecture 6 – Mass Analyzers