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

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. He*(g)+nH2O(g)  He(g) + (H2O)n-1H+(g) + OH-(g)
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,
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 , we estimate that aerosols contributed /-0.81oC to the observed Arctic surface temperature increase of 1.48+/-0.28oC. “
NATURE GEOSCIENCE | VOL 2 | APRIL 2009 |

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 Aircraft Aerosol Time of Flight Mass Spectrometer
Pumps remove the background gas
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
A spectrum identified as OC-Sulfate-Nitrate
Date, location, altitude, temperature and particle aerodynamic diameter
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,
Nature Geoscience. 2009, 2,