Transcript Mass Spectrometry Ionization Techniques

Mass Spectrometry Ionization
Techniques
Ryan Sargeant
Topics in Analytical Chemistry
The Undergraduate Mass Spectrometer
Organic Chemistry, Carey 6th ed
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
Spectrometric Identification of Organic Compounds, Silverstein 2005
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
Spectrometric Identification of Organic Compounds, Silverstein 2005
Electrospray Ionization (ESI)
• Liquid phase samples of large size (biomolecules)
can be ionized using ESI
– This is often
coupled with LC (LCMS)
– The solvated
analyte is fed
through a capillary
tube with very high
charge differential
– The charged droplet
evaporates and
ionizes the analyte
CRM vs IDM
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)
Spectrometric Identification of Organic Compounds, Silverstein 2005
Ambient Ionization Methods
• The primary drawbacks to most ionization methods
are:
1. The ions are formed in a vacuum
2. The ions require a solvent
3. 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
DESI
• Desorption Electrospray Ionization was first
reported in 2004 by Graham Cook
(H2O/CH3OH)
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)
DESI Applications
• DESI can be used in a HUGE variety of applications
1. Pharmaceutical testing
– Quality control/assurance
– Counterfeit identification
2. Chemical weapons
3. Explosive residues
4. Latent fingerprints
Cialis vs Viagra
Limits of Detection
• DESI analysis of explosive compounds represent
limit of detection capabilities
Cocaine Fingerprints
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”
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
DART Applications
• DART has many of the same advantages as DESI
1. Little or no sample preparation
2. In situ analysis
3. Adaptable to nearly any matrix
• DART is used in many of the same areas
– Forensics
– Food Inspection
– Etc.
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
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
Applications of Mass
Spectrometry is Aerosol Analysis
Ryan Sargeant
Topics in Analytical Chemistry
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
Asia’s Brown Cloud
• Aerosols generally cool the Earth’s surface at the
cost of a warmer upper atmosphere
Arctic Warming and Asian Soot
• Recent global climate models suggest that black
aerosols are leading to additional Arctic warming
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
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
1. laser desorption ionization
2. Thermal desorption  electron impact ionization
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
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
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
A-ATOFMS Data Compilation
•
Ground level and after take-off data (N. Colorado)
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
References
1.
2.
3.
4.
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=N
SF&cntn_id=109712&preview=false