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ESI-MS: Electrospray Ionization Mass Spectrometry

ESI-MS: Electrospray Ionization Mass Spectrometry. Jason Russell USD - Chem. 730 Dec. 4 th , 2006. Presentation Overview. What is ESI-MS? Features of ESI-MS Brief history of the origins of ESI How ESI-MS works Two theories of gas phase ion formation from liquid droplets

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ESI-MS: Electrospray Ionization Mass Spectrometry

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  1. ESI-MS:Electrospray Ionization Mass Spectrometry Jason Russell USD - Chem. 730 Dec. 4th, 2006

  2. Presentation Overview • What is ESI-MS? • Features of ESI-MS • Brief history of the origins of ESI • How ESI-MS works • Two theories of gas phase ion formation from liquid droplets • Example Applications

  3. What is Electrospray Ionization Mass Spectrometry (ESI-MS)? • The technique of electrospray transfers ions present in solution into the gas phase • Gas phase ions can then be analyzed in a mass spec • The mechanism(s) of ionization will be addressed later

  4. Features of ESI-MS • Can produce multiply charged molecules, decreasing m/z allowing the mass determination of up to 10^7 g/mol • Considered a “soft” ionization method • Can preserve solution phase noncovalent interactions in the gas phase • Can study 3-D molecular conformations • Can obtain the molecular mass • Conditions can be adjusted to promote fragmentation usable for molecule identification (usually by using a triple-quad MS)

  5. Feature of ESI-MS (cont.) • Samples are introduced in solution and at atmospheric pressure • Can be interfaced with solution-based separation methods • HPLC/UPLC • CE • Two basic modes of operation • Positive mode – usually for basic molecules • Negative mode – usually for acidic molecules

  6. Origins of ESI • Electrospray – well known phenomenon since the 1800’s • John Zeleney (Univ. Minnesota, Yale) • Early 1900’s: Able to see that that charged droplets broke apart after the solvent had evaporated • Confirmed the prediction made by Rayleigh in the 1800’s, known as the Rayleigh limit • Coulombic repulsion at a droplet surface would reach a critical value overcoming the surface tension • Result was smaller daughter droplets

  7. Origins of ESI (cont.) • Malcolm Dole (Northwestern, Baylor) • Pioneered the work that laid the foundation for what is now known as ESI-MS • Theorized that continued Rayleigh Limit occurrences in charged droplets containing multiple molecules would eventually yield a droplet containing a single charged molecule • Result was a gas phase ionized molecule • 1968, paper describing the ESI technique using polystyrene and a magnetic sector MS • Developed the charge residue model (CRM)

  8. Origins of ESI (cont.) • John Fenn et. al., • Built upon the work of Dole • Countercurrent desolvating gas • Experimented with smaller molecules and used a quadrupole MS • Successfully mated ESI-MS with LC

  9. How ESI-MS Works • There have been several modifications from the original design of Fenn et. al., but the general concept remains the same

  10. Diagram of a Second-generation ESI-MS Apparatus from Fenn’s Lab (Late 1980’s) J. Fenn. J. Biomolecular Techniques. 13, 101-118(2002).

  11. N. Cech & B. Enke. Mass Spec. Rev. 20,6, 362-387(2001).

  12. P. Kebarle, J. Mass Spec. 35, 804-817(2000).

  13. Droplet fission may occur with the ejection of up to 20 or more daughter droplets • Radius = 1/10 of parent droplet • Can be observed with when r > 1um • Daughter droplets can be produced with r = 10 nm in 100-500 us • Daughter droplets carry away 2% of the parent mass, but 15% of the charge R. Cole. “Electrospray Ionization Mass Spectrometry: Fundamentals, Instrumentation, and Applications”. John Wiley and Sons, Inc. 1997

  14. P. Kebarle, J. Mass Spec. 35, 804-817(2000).

  15. Close-up of Droplet Formation at the Needle Tip http://www.newobjective.com/electrospray/index.html

  16. Electrospray Process Viewed Through a High Resolution Microscope With Increasing Voltages at the Needle Tip http://www.newobjective.com/electrospray/spray_anim.html

  17. Theories of Ion Transfer to the Gas Phase • Charge Residue Model (M. Dole) • Ion Evaporation Model (Iribarne and Thomson) • With very small radii (< 1nm), the two processes are currently indistinguishable • The IEM model is viewed as the most likely mechanism, although there is experimental evidence to support both

  18. Example Applications

  19. Very Large Mw Molecules J. Fenn & T. Nohmi. J. Am. Chem. Soc. 114, 3241-3246(1992)

  20. Proteins (Myglobin) N. Cech & B. Enke. Mass Spec. Rev. 20,6, 362-387(2001).

  21. Multiple Charging and Deconvolution – Bovine Serum Albumin R. BakhTiar & F. Tse. Mutagenesis. 15(5), 415-430(2000).

  22. Estimation of protein surface areas in Solution • Determination of dissociation constants for protein-ligand complexes • Relating polarity character of peptides and small proteins by their ESI response • Amino acid analysis

  23. CE-ESI-MS Amino Acid Determination T. Soga & D. Heiger. Anal. Chem. 72, 1236-1241(2000)

  24. Monitoring Electrochemical Reactions G. Van Berkel & K. Asano. Anal. Chem. 76, 1493-1499(2004)

  25. G. Van Berkel & K. Asano. Anal. Chem. 76, 1493-1499(2004)

  26. Thank-you Questions/Comments?

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