pulsed glow discharge mass spectrometry: an ionization source for aerosol analysis and laser...
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Pulsed Glow Discharge Mass Spectrometry:
An Ionization Source forAerosol Analysis and Laser Sampling
Farzad Fani-Pakdel
Qualifying ExaminationUniversity 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 -100m) in a gas.
Biological Aerosols:
• Viruses: 0.01 - 0.3 micron• Bacteria: 0.5 – 10 micron• Pollen: 5-100 micron
• Allergy and sickness
• Contagious diseases
• Biological warfare
Examples:Atmospheric Aerosols:
• Dust• Fog• Haze • Smoke• Sea spray particles
• Air pollution (Acidic rain)
• Atmospheric reactions
• Material transfer
• War generated particles
Significance:
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Chemical Characterization of Aerosols
hv
Nano device
Sampling
Spectroscopy: non-destructive, surface onlyNano sensors: non-destructive, selective, surface onlyMass spectrometry: destructive, core and surface both possibleImportance: chemical contamination or bio hazard in core
Ionization
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Ideal Ionization Technique
Soft ionizationprovides surface information, at the molecular level
CI
ICP
Intense ionizationProvides surface and bulkInformation, at atomic level
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
+-
Anode (+)Cathode (-)
e
Negative Glow
Ar
Ar+
ArAr+
Ar *
e
Penning ionization by meta-stable argon, Electron ionization
eCu Cu+
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time
V
Pulsed Glow Discharge
High energy electrons (ICP)Pre-peak
Fragmentation
PlateauPenning ionizationSoft, ( CI )After peak
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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 particlesbulk vs. surface chemical analysis
CdSe / ZnS nano particles
Gold nano particles
with hydrocarbon chains
MgCl2 , NaCl mixed nano particles
Silicanano particleswith peptides
on surface
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Experimental Setup
pressure gauge
Ar
exhaust
Needle ValveNebulizer
TOF GD
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
Cathode
O-ring
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
1.0
0.5
0.3
0.7
0.3
0.75
0.3
0.1
0.3
0.1
0.8
AnodeInsulator
Cathodebase
Scale in inches
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22 24 26
2
4
sign
al: m
v
m/z
Tap water
DI water
Na-Mg solution
Preliminary Results
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 sample’s 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
Laser Induced Back Ablation
mirror
Lenz
Sample on a quartz window
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Laser
Pulsed Laser Induced Forward Transfer
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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:1. 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.
2. W.W. Harrison, C. Yang and E. Oxley, Anal. Chem., 2001, 73, 480A-487A
3. 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
4. A. B. Bullock, P. R. Bolton, Appl. Phys., 1999, 85, No. 1, 460-465
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Acknowledgments:
• Dr Omenetto• Dr Harrison • Dr Igor Gornushkin
• Dr Winefordner• Dr Smith• Dr Kevin Turnery
• Committee members• Winefordner-Omenetto- Smith group• Friends from Yost / Martin group• Machine shop• Electronic Shop