Handout: CH3F2 Mass Spectrometry, Barrow Lecture 2023-2024

CH3F2 (Advanced Analytical Chemistry) Mass Spectrometry: Analyzers Dr. Mark P. Barrow Physics revision Charge and potential Charge is a physical property of matter: charged particles experience a force when placed in an electromagnetic field Coulomb’s law: 𝑞! 𝑞" 𝐹= 4𝜋𝜀# 𝑟 " where F is force (in newt...

CH3F2 (Advanced Analytical Chemistry) Mass Spectrometry: Analyzers Dr. Mark P. Barrow Physics revision Charge and potential Charge is a physical property of matter: charged particles experience a force when placed in an electromagnetic field Coulomb’s law: 𝑞! 𝑞" 𝐹= 4𝜋𝜀# 𝑟 " where F is force (in newtons, N), q is charge (in coulombs, C), ε0 is the permittivity of free space, and r is the separation between the charges (in metres, m) Electric potential: amount of work (energy) required to move a charged particle from one point in an electric field to another Electric potential is measured in J C-1 (or volts, V) A note about potentials Potential energy: energy that is stored, such as due to an object’s position Can be converted to kinetic energy (movement), for example Gravitational potential energy “Voltage” is the difference between two electric potentials https://getoutside.ordnancesurvey.co.uk/guides/understanding-map-contour-lines-for-beginners/ A note about potentials https://www.rei.com/learn/expert-advice/topo-maps-how-to-use.html A note about potentials Simulation of potential energy surface for a quadrupole using SIMION 7 Fleming’s left hand rule Lorentz force: 𝐹 = 𝑞𝐸 + 𝑞𝑣𝐵 Force Magnetic field where F is the force (in newtons, N), q is the charge (in coulombs, C), E is the electric field (in volts per metre, V/m), v is the particle’s velocity (in ms-1), and B is the magnetic flux density (in tesla, T) Therefore a charged particle which is moving in the presence of a magnetic field will experience a force https://commons.wikimedia.org/wiki/User:Jfmelero Current Sector, quadrupole, and ion trap instruments Sector instruments “Mass Spectrometry: A textbook,” Jürgen Gross, Springer, ISBN: 978-3-319-54397-0 Sector instruments Sector instruments "Mass Spectrometry," James McCullagh and Neil Oldham, Oxford Chemistry Primers, ISBN: 9780198789048 Quadrupole "Mass Spectrometry," James McCullagh and Neil Oldham, Oxford Chemistry Primers, ISBN: 9780198789048 Quadrupole + + + To detector + Ions with stable oscillations through quadrupole at a particular RF and DC reach detector All other ions do not make it through the quadrupole Quadrupole az -0.4 z stability -0.2 Stable z&r -0.2 + + -0.6 A± = U ± Vsin(ωt) b=1.0 qz=.908 0.0 -0.4 + “Matthieu equation” Operating line r stability 0.5 1.0 1.5 qz qz = 4eV mw 2 r 2 qz ∝ V/m qz ∝ fion an = 8eU mw 2 r 2 az ∝ U/m Quadrupole Quadrupole is a scanning or sequential analyzer Only one m/z measured at a time Peak width determined by ratio between DC and RF (U : V cos wt) Mass spectrum Keep ratio between DC and RF constant Increase amplitude of RF and DC Quadrupole High resolution m/z1 < m/z2 < m/z3 Ratio between DC and RF kept constant Poor resolution DC and RF amplitude increased together Ions are transmitted one at a time RF only, transmit all ions qz = "Mass Spectrometry," James McCullagh and Neil Oldham, Oxford Chemistry Primers, ISBN: 9780198789048 4eV mw 2 r 2 Ion traps Similar principle to quadrupoles Ions trapped, motion damped by collisions with gas By changing RF, “scan” ions out to reach detector “Mass Spectrometry: A textbook,” Jürgen Gross, Springer, ISBN: 978-3-319-54397-0 Time-offlight (TOF) instruments Time-of-flight (TOF) TOF is a pulsed experiment MALDI (pulsed laser) Can use continuous ion sources (e.g. ESI) if have a way to make the experiment pulsed, such as accelerating the ions orthogonally to detector TOF requires a small kinetic energy distribution in the ions TOF requires a detector/oscilloscope/digitizer that’s MUCH faster than the ion flight time (typically microseconds) Time-of-flight (TOF) Ions accelerated from ion source Kinetic energy, Ekin of ions: Ekin = ½ m v2 = z e Vacc where m is the mass of the ion, v is the velocity, z is the number of charges, e is the elementary charge, and Vacc is the accelerating potential We know that v = d/t where d is the distance and t is time Time-of-flight (TOF) Therefore: ½ m (d/t)2 = z e Vacc m/z = 2 e Vacc (t/d)2 d and Vacc are constants, so: m/z ∝ t2 m/z is proportional to the square of the time taken to reach the detector (time-of-flight) Time-of-flight (TOF): linear TOF Laser Source Oscilloscope S + + Vacc + + D (field free drift region) Time-of-flight (TOF): Reflectron TOF Laser Source S + + Vs Vr ≈ Vs D1 (first field free drift region) + + First Detector deflector + + Oscilloscope D2 (second field free drift region) Second detector Time-of-flight (TOF): orthogonal TOF Enables use of continuous ion sources, such as ESI Reduces temporal spread in ions due to small kinetic energy differences (improves resolving power) Spread in times No spread in times "Mass Spectrometry," James McCullagh and Neil Oldham, Oxford Chemistry Primers, ISBN: 9780198789048 Fourier transform mass spectrometry (FTMS) Fourier transform mass spectrometry (FTMS) Two instrument types: Fourier transform ion cyclotron resonance (FTICR) Orbitrap Instead of ions hitting a detector, ion motion is detected (“listened to”) Longer detection increases resolving power Typically detect for seconds “Fourier transform” used to determine frequencies (Hz) of multiple signals detected (signal as a function of time, seconds) er electron (coulombs, C). transform rgedFourier particle, such asion ancyclotron ion, willresonance begin to (FT-ICR) precess he center of the magnetic field axis, resulting in an State-of-the-art, offersas highest his motion is known the performance ‘‘cyclotron motion.’’ The n frequency is related magnet to theformass-to-charge ratio of Uses superconducting high magnetic and is field shown in eqns. (3a) and (3b): Expensive (typically ~£1 qB million or more) v~ (3a) Frequency of ion is inversely m proportional to m/z (remember q = z e) qB f~ 2pm where B is the magnetic field strength in tesla, m is the mass in kg, q 21in Hz is the charge in Coulombs, and f is the cyclotron frequency (3b) mass of the ion (kg), and v (rad s ) and f (hertz, Hz) essions for the cyclotron frequency. It can therefore be charge per electron (coulombs, C). nd ion sources must be A charged particle, such as an ion, will b transform resonance (FT-ICR) om Fourier a neutral sample.ion cyclotron about the center of the magnetic field axis, olid, liquid, or a gas, orbit. This motion used. The ions are Detection using two is known as the ‘‘cyclotro plates cyclotrondetection frequency is related to the mass-to of the mass spectroDetect all ions at same (3b): time the ion and is shown in eqns. (3a) and case of FT-ICR mass as they orbit qB atedAnalyst, externally in a 2005, 130, pp. 18-28 v~ to a container known m ical or cylindrical in qB ocated within a strong f~ 2pm ng a superconducting representation of a m is the mass of the ion (kg), and v (rad s21) a Spectrometry," James McCullagh and Neil Oldham, Oxford Chemistry Primers, ISBN: 9780198789048 h as "Mass the Infinity Cell are expressions for the cyclotron frequency. It Hyperfine detail by FT-ICR MS Substance P: C63H98N18O13S “Mass Spectrometry: A textbook,” Jürgen Gross, Springer, ISBN: 978-3-319-54397-0 Orbitrap Second highest performance No superconducting magnet Expensive (typically ~£1 million) Frequency of ion (in rad s-1) is inversely proportional to square root of m/z (remember q = z e) Orbitrap q=ze "Mass Spectrometry," James McCullagh and Neil Oldham, Oxford Chemistry Primers, ISBN: 9780198789048 Comparison of analyzers "Mass Spectrometry," James McCullagh and Neil Oldham, Oxford Chemistry Primers, ISBN: 9780198789048 T Advantages Disadvantages Quadrupole / ion trap Small Cheap Fast Poor resolving power Poor mass accuracy Time-of-flight (TOF) Mid-range resolving power Sensitive to temperature Relatively cheap Simple Very fast (multiple spectra per second) Theoretically infinite m/z range Fourier transform ion cyclotron resonance (FTICR) Highest resolving power Best mass accuracy Many ionization methods Many fragmentation methods Slow (seconds per scan) Expensive Require user expertise Need cryogens for magnet Need ultrahigh vacuum (UHV) Orbitrap Second highest resolving power Second best mass accuracy Selection of ionization methods Selection of fragmentation methods Relatively simple Slow (seconds per scan) Expensive Need ultrahigh vacuum (UHV) Less flexibility than FTICR MS Next lecture: Tandem mass spectrometry