Pulsed Glow Discharge Mass Spectrometry:

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Pulsed Glow Discharge Mass Spectrometry An
Ionization Source forAerosol Analysis and Laser
Sampling Farzad Fani-Pakdel Qualifying
Examination University of Florida - Department of
Chemistry Division of Analytical Chemistry
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Outline
Introduction Aerosols Aerosols
characterization Glow discharge Research
objective Experimental Instrumental set-up
Particle introduction into system Preliminary
Results Laser Sampling Importance and
application Cathode design
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Aerosols
Suspension of fine solid or liquid particles (3
nm -100mm) in a gas.
Examples

• Atmospheric Aerosols
• Dust
• Fog
• Haze
• Smoke
• Sea spray particles

• Biological Aerosols
• Viruses 0.01 - 0.3 micron
• Bacteria 0.5 10 micron
• Pollen 5-100 micron

Significance

• Air pollution (Acidic rain)
• Atmospheric reactions
• Material transfer
• War generated particles

• Allergy and sickness
• Contagious diseases
• Biological warfare

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Chemical Characterization of Aerosols
Spectroscopy non-destructive, surface only Nano
sensors non-destructive, selective, surface
only Mass spectrometry destructive, core and
surface both possible Importance chemical
contamination or bio hazard in core
hv
Sampling
Ionization
Nano device
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Ideal Ionization Technique
Soft ionization provides surface information, at
the molecular level
CI
Intense ionization Provides surface and
bulk Information, at atomic level
ICP
A moderate ionization like EI will result in
fragmentation
Pulsed glow discharge is an ionization source
capable of ionization at all these levels at the
same time.
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Glow Discharge Ionization Source
Penning ionization by meta-stable argon, Electron
ionization
Anode ()
Cathode (-)
Negative Glow
Ar
e
Ar
e
Ar
Ar
Ar
Cu
Cu
e
-

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Pulsed Glow Discharge
Fragmentation Plateau
High energy electrons (ICP) Pre-peak
Penning ionization Soft, ( CI ) After peak
V
time
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Schematics of a Glow Discharge -Time of Flight
Instrument
Majidi, et al., Anal. Chem., 2003, 75, 1983-1996
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Research Objectives
Application of pulsed GD - TOF Mass Spectrometry
for characterization of different particles bulk
vs. surface chemical analysis
Silica nano particles with peptides on surface
Gold nano particles with hydrocarbon chains
CdSe / ZnS nano particles
MgCl2 , NaCl mixed nano particles
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Experimental Setup
GD
TOF
Figure is modified from the original Eric Oxley,
Ph.D. Dissertation, Department of Chemistry,
University of Florida, 2002.
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Glow Discharge Source
O-ring
Cathode
Eric Oxley, Ph.D. Dissertation, Department of
Chemistry, University of Florida, 2002.
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Particle Introduction 1
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Particle Introduction 2
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Particle Introduction 3
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Particle Introduction 2 Cathode Design
Cathode base
Scale in inches
Insulator
Anode
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Preliminary Results
Tap water
Na-Mg solution
DI water
To examine the sample introduction design, a
sodium chloride-magnesium nitrate
solution(1000ppm of each) was nebulized to
produce particles of about 100nm size
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Laser Sampling
Introduction of particles /atoms into discharge
by laser pulse from the samples back side.

• Synchronized sample introduction is possible
• Study of non-conductive thin films also possible,
  surface analysis of thin films (brain slice)
• Sampling yield improves
• Back side sampling (LIFT or LIBA) has the
  advantage of sampling directionality

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Laser Induced Back Ablation
Laser
mirror
Lenz
Sample on a quartz window
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Pulsed Laser Induced Forward Transfer
Laser
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Summary
Glow discharge time of flight mass spectrometry
can be used for surface and core chemical
characterization of particles Cathode of the
source needs to be modified for sample
introduction An orifice in the cathode seems to
be a proper way of particle introduction Laser
sampling can be used for synchronized
introduction of particles and also analysis of
thin films (useful for non-conductive samples)
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References

• Eric Oxley, The Microsecond Pulsed Glow
  Discharge Developments in Time of Flight Mass
  Spectrometry and Atomic Emission Spectrometry.,
  Ph.D. Dissertation, Department of Chemistry,
  University of Florida, 2002.
• W.W. Harrison, C. Yang and E. Oxley, Anal. Chem.,
  2001, 73, 480A-487A
• C.L. Lewis, M.A. Moser, D.E. Dale, Jr., W. Hang,
  C. Hassel, F.L. King and V. Majidi, Anal. Chem.,
  2003, 75, 1983-1996
• A. B. Bullock, P. R. Bolton, Appl. Phys., 1999,
  85, No. 1, 460-465

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Acknowledgments

• Dr Winefordner
• Dr Smith
• Dr Kevin Turnery

• Dr Omenetto
• Dr Harrison
• Dr Igor Gornushkin

• Committee members
• Winefordner-Omenetto- Smith group
• Friends from Yost / Martin group
• Machine shop
• Electronic Shop