RelativeResourceManager(18) - Mass spectrometry Part 2 Chem...

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Mass spectrometry: Part 2 Chem 420 November 05, 2008 Professor Ryan C. Bailey All figures not from Skoog come from Contemporary Instrumental Analysis by Rubinson and Rubinson
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Problem Set #4 z Posted on Compass z Due before Thursday, November 6 at 12 noon z Turn in at 68 RAL z Correction to Problem 6b. Should read: “What range of accelerating voltages would be required to scan the mass range between 16 and 250, for singly charged ions, if the field strength is held constant?”
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Mass analyzers z Sort ions based upon m/z ratio z Exert forces upon ions in order to differentiate m/z ratios z Efficiency of ion sorting described by resolution: z Common types z Magnetic sector z Double-focusing z Time-of-flight z Quadrupole z Quadrupole ion trap z FT-Ion cyclotron resonance is the mass difference between the two peaks is the average mass of the peaks m m m R m Δ = Δ
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Magnetic sector analyzers z Ions are injected into a circular path magnet and only those of a certain m/z ratio are able to balance the centripetal and magnetic forces in order to make it out the other side. z Mass selection is achieved by sweeping the field, B (typically) or V . z Resolution 2000 2 2 2 22 1 2 2 Mc mv FB z e v F r mv Bzer Bzev v rm KE zeV mv mB r e zV == = http://www.wooster.edu/Chemistry/analytical/ms/default.html B =magnetic field strength e =electron charge v =velocity V =accelerating voltage
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Limitations of magnetic sector z Not all ions of same m/z have identical kinetic energy z Boltzmann distribution out of ion source z Causes broadening in m/z transmitted z Solution: Use a second focusing element
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Double focusing analyzer z Ions are first passed through electrostatic energy filter to isolate a single kinetic energy z Resolution 100,000 Mattauch-Herzog configuration • Better for array detectors that capture entire mass spectra Neir-Johnson design • Single channel measurements
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RelativeResourceManager(18) - Mass spectrometry Part 2 Chem...

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