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Mass Spectrometry Ionization Techniques

Mass Spectrometry Ionization Techniques. Ryan Sargeant Topics in Analytical Chemistry. The Undergraduate Mass Spectrometer. Organic Chemistry, Carey 6 th ed. Electron Impact (EI) Ionization. Electron impact is the most common form of ionization

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Mass Spectrometry Ionization Techniques

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  1. Mass Spectrometry Ionization Techniques Ryan Sargeant Topics in Analytical Chemistry

  2. The Undergraduate Mass Spectrometer Organic Chemistry, Carey 6th ed

  3. Electron Impact (EI) Ionization • Electron impact is the most common form of ionization • Very high energy electrons (~70eV) bombard the gas phase sample and form the cation radical • Ionization only requires ~15 eV • Bond cleavage requires ~3 – 10 eV • Fragmentation patterns are predictable • Leads the formation of the large databases • The primary weakness is the loss of the molecular ion peak

  4. Spectrometric Identification of Organic Compounds, Silverstein 2005

  5. Chemical Ionization (CI) • CI is a “soft” ionization technique • Leaves the molecular ion intact • Ionization occurs due to collisions of ionized gases with the target analyte http://riodb01.ibase.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi

  6. Spectrometric Identification of Organic Compounds, Silverstein 2005

  7. Electrospray Ionization (ESI) • Liquid phase samples of large size (biomolecules) can be ionized using ESI • This is often coupled with LC (LC-MS) • The solvated analyte is fed through a capillary tube with very high charge differential • The charged droplet evaporates and ionizes the analyte

  8. CRM vs IDM

  9. Desorption Ionization Methods • Other “soft” ionization methods use bombardment methods similar to CI • Fast Atom Bombardment (FAB) • Matrix Assisted Laser Desorption Ionization (MALDI) • These methods depend on a liquid matrix to absorb the excess ionization energy • Much larger molecular ions can be formed (> 20 kDa)

  10. Spectrometric Identification of Organic Compounds, Silverstein 2005

  11. Ambient Ionization Methods • The primary drawbacks to most ionization methods are: • The ions are formed in a vacuum • The ions require a solvent • No in situ analysis • Graham Cook coined the term “Ambient Ionization Methods” in 2004 to describe developing techniques to analyze samples in their native state • DESI and DART

  12. DESI • Desorption Electrospray Ionization was first reported in 2004 by Graham Cook (H2O/CH3OH)

  13. DESI Mechanism • DESI occurs when analyte particles are solvated by an ionized solvent flow • The solvated analyte is ejected from the sample and swept toward the mass analyzer • The mechanism and spectra are very similar to ESI Raw urinalysis (2 mL)

  14. DESI Applications • DESI can be used in a HUGE variety of applications • Pharmaceutical testing • Quality control/assurance • Counterfeit identification • Chemical weapons • Explosive residues • Latent fingerprints

  15. Cialis vs Viagra

  16. Limits of Detection • DESI analysis of explosive compounds represent limit of detection capabilities

  17. Cocaine Fingerprints

  18. DART • Direct analysis in real time (DART) was initially developed in 2003 and reported in 2005 • Very similar to DESI (gas solvent instead of liquid) • The original experiments picked up contaminants (glue) “far removed from the laboratory”

  19. DART Chemistry • The chemical reactions underlying DART as not as well understood as its implementation and usage • In general: He*(g)+nH2O(g)  He(g) + (H2O)n-1H+(g) + OH-(g) DART Background

  20. DART Applications • DART has many of the same advantages as DESI • Little or no sample preparation • In situ analysis • Adaptable to nearly any matrix • DART is used in many of the same areas • Forensics • Food Inspection • Etc.

  21. References • Spectrometric Identification of Organic Compounds, 7th ed, Silverstein, Webster, and Kiemle, John Wiley and Sons, 2005 • Hogan, C. J., Carroll, J. A., Rohrs, H. W., Biswas, P., Gross, M. L., Anal. Chem., 2009, 81 (1), pp 369–377 • Ifa, R. I., Manicke, N. E., Dill, A. L., Cooks R. G.; Science, 2008, 321, 805 • Cooks, R. G., Ouyang, Z., Takats, Z., Wiseman, J. M.; Science, 2006, 311, 1566 • Kelesidis, T., Kelesidis, I., Rafailidis, P. I., Falagas, M. E.; Journal of Antimicrobial Chemotherapy, 2007, 60, 214–236 • Esquenazi, E., Pieter C. Dorrestein P. C., and Gerwick, W. H.; PNAS, 2009, 106(18), 7269–7270 • Cody, R. B., Laramee, J. A., Durst, H. G.; Anal. Chem. 2005, 77, 2297-2302 • Harris, G. A., Fernandez, F. M.; Anal. Chem. 2009, 81, 322–329 • Cody, R. B.; Anal. Chem. 2009, 81, 1101–1107

  22. Applications of Mass Spectrometry is Aerosol Analysis Ryan Sargeant Topics in Analytical Chemistry

  23. Environmental Monitoring of Aerosols • Atmospheric aerosols are large particles of variable composition • That they have a role in global climate is apparent, but the degree of influence on the climate remains unclear • Various forms of real time MS have been employed to assist in the understanding of atmospheric aerosols

  24. Asia’s Brown Cloud • Aerosols generally cool the Earth’s surface at the cost of a warmer upper atmosphere

  25. Arctic Warming and Asian Soot • Recent global climate models suggest that black aerosols are leading to additional Arctic warming

  26. The Shindell Conclusions • The contribution of black soot to Arctic warming had been suggested for ~7-8 years • Drew Shindell (NASA) tried to quantify the warming contributions using molecular moles in a recent Nature paper “During 1976-2007, we estimate that aerosols contributed 1.090+/-0.81oC to the observed Arctic surface temperature increase of 1.48+/-0.28oC. “ NATURE GEOSCIENCE | VOL 2 | APRIL 2009 | 294-300

  27. Analytical Techniques • Much of the aerosol data is collected by remote airplanes • The MS analysis is performed by an instrument mounted on the airplane • Analyte ionization usually occurs via • laser desorption ionization • Thermal desorption  electron impact ionization

  28. A-ATOFMS Pumps remove the background gas • Aircraft Aerosol Time of Flight Mass Spectrometer Dual lasers measure aerodynamic diameter based on time of flight Mirrors focus laser signal and particles are pulsed with laser as they enter the MS

  29. A-ATOFMS • Aircraft Aerosol Time of Flight Mass Spectrometer Ions enter through the Extractor Positive ions head to one detector and negative ions head to the other

  30. A-ATOFMS Sample Spectrum Date, location, altitude, temperature and particle aerodynamic diameter • A spectrum identified as OC-Sulfate-Nitrate Both positive and negative ion spectra are reported

  31. A-ATOFMS Data Compilation • Ground level and after take-off data (N. Colorado)

  32. Objectives • The primarily objective of the data collection has been to determine the types of aerosols present (and to track them to their source) • Once the type of particle is identified, radiative forcing can be calculated

  33. References • Anal. Chem. 2009, 81, 1792–1800 • Anal. Chem. 2005, 77, 3861-3886 • Nature Geoscience. 2009, 2, 293-299 • http://www.nsf.gov/news/news_summ.jsp?org=NSF&cntn_id=109712&preview=false

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