Mass Analyzers Double Focusing Magnetic Sector Quadrupole Mass Filter Quadrupole Ion Trap Linear Time-of-Flight (TOF) Reflectron TOF Fourier Transform Ion Cyclotron Resonance (FT-ICR-MS)

Mass Analyzers Resolution –R = m / Δm Accuracy/Precision –mass measurement accuracy/reproducibility Transmission –% of ions allowed through the analyzer Mass Range –Highest m/z that can be analyzed Scan Speed –How many spectra per unit of time

Double-Focusing Magnetic Sector

Double-Focusing Magnetic Sector Magnetic Sector mqmq r 2 B 2 2V = B = magnetic field strength r = radius of curvature in magnetic field V = accelerating voltage m = ion mass q = ion charge All ions of the same m/z will have the same radius Only if the Ion kinetic energy is constant

Double-Focusing Magnetic Sector Electric Sector r 2E k qE = E k = ion kinetic energy r = radius of curvature in electric field E = magnitude of electric field q = ion charge All ions exiting the electric sector have the same kinetic energy

Double-Focusing Magnetic Sector

Magnetic Sector Typically a voltage of 5-10kV is used to accelerate ions To obtain a full spectrum, magnetic field is scanned To obtain a HR scan, voltage is scanned at constant magnetic field To gain maximum sensitivity at one mass SIM scan is done –B and E are constant for one or more masses

Advantages Very High Resolution (60,000) High Accuracy (<5 ppm) 10,000 Mass Range Disadvantages Very Expensive Requires Skilled Operator Difficult to Interface to ESI Low resolution MS/MS without multiple analyzers Double-Focusing Magnetic Sector

Quadrupole Mass Filter

Quadrupole E = U - Vcos(2πνt) E = potential applied to the rods U = DC potential V = RF amplitude ν = RF frequency t = time Quadrupole is scanned at a constant U/V

Quadrupole Mass Filter

Quadrupole Typically U varies from V V varies from V (-3000 to +3000) Scanning U/V at a fixed ratio gives a full scan –Higher values of U/V give higher resolution RF only (U=0) transmits all ions Higher sensitivity through SIM scan –Jumping to specific points on the U/V line

Advantages Inexpensive Easily Interfaced to Many Ionization Methods Disadvantages Low Resolution (<4000) Low Accuracy (>100ppm) MS/MS requires multiple analyzers Low Mass Range (<4000) Slow Scanning Quadrupole Mass Filter

Quadrupole Ion Trap

Ions are injected into the trap and all ions are trapped RF and DC are scanned to sequentially eject ions for detection Specific ions can be trapped while others are ejected Ion velocity can be increased to induced fragmentation

Advantages Inexpensive Easily Interfaced to Many Ionization Methods MS/MS in one analyzer Disadvantages Low Resolution (<4000) Low Accuracy (>100ppm) Space Charging Causes Mass Shifts Low Mass Range (<4000) Slow Scanning Quadrupole Ion Trap

Time-of-Flight (TOF) mv 2 2 zV s = E k = kinetic energy v = ion velocity d = flight distance t = flight time V s = accelerating voltage m = ion mass q = ion charge All ions of the same m/z will have the same flight time Only if the Ion kinetic energy is constant = EkEk dtdt = vt 2 = mzmz d 2 2V s

Advantages Extremely High Mass Range (>1 MDa) Fast Scanning Disadvantages Low Resolution (4000) Low Accuracy (>200ppm) MS/MS not possible Linear Time-of-Flight (TOF)

TOF Ions are accelerated with 5-35 kV Space focusing of source ions is accomplished by delayed extraction An electrostatic analyzer (reflectron) is used correct for kinetic energy spread

Reflectron Time-of-Flight (MALDI-TOF)

Reflectron Time-of-Flight (ESI-TOF) Courtesy Bruker Datonics BioTOF user’s Manual

Reflectron Time-of-Flight (TOF)

Advantages High Resolution (>20,000 in some models) High Accuracy (<3ppm) 10,000 Mass Range Fast Scanning >100 Hz Disadvantages Low Resolution for MS/MS (PSD) Reflectron Time-of-Flight (TOF)

FT-ICR-MS

v 2πr f = B = magnetic field strength v = ion velocity f = orbital frequency m = ion mass q = ion charge r= orbital radius At constant B, orbital frequency is inversely related to m/z Frequency is independent of kinetic energy qvB = mv 2 r vrvr 2πf = = qB 2πm Centripital Force Circular Path r and v drop out

FT-ICR-MS Ions are all trapped radially by a magnetic field (typically 3-15 T) Axial trapping by DC potential Ion radius is increased by RF pulse –also brings orbits into phase Orbiting ions induce RF current in receiver plates –Image current is a composite of all frequences in time domain FFT gives frequency (mass) spectrum

FT-ICR-MS

m/z Δm = a.u. 1/Δm = a.u. mass = a.u m/z Electrospray: Broadband Spectrum of Bovine Serum Albumin (66kDa) 7.0T Actively Shielded Magnet

FT-ICR-MS Electrospray: Deconvoluted Spectrum of Bovine Serum Albumin (66kDa) 7.0T Actively Shielded Magnet m/z Δm = a.u.

Advantages Extremely High Resolution (>500,000) Very Good Accuracy (<1 ppm) MS/MS in one analyzer Disadvantages Expensive Requires Superconducting Magnet Slow MS/MS FT-ICR-MS