Proton Transfer Reaction Ion Trap Mass Spectrometer PTRITMS: Next Generation Aircraft Instrumentatio

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Proton Transfer Reaction Ion Trap Mass
Spectrometer (PTR-ITMS) Next Generation Aircraft
Instrumentation for Gas Phase Organic Analysis

• Michael Alexander and Tom Jobson
• ASP Science Team Workshop
• Charleston, SC
• January 2005

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Motivations and Connection of PTR-ITMS to Overall
ASP

• Measurements of VOC important in understanding
  SOA formation heterogeneous reactions on
  particles, acid catalyzed reactions, oxidation of
  terpenes
• Real time measurements of VOC in conjunction with
  particle size and composition measurements (AMS)
• Time resolution is critical to making relevant
  measurements of VOC
• Aircraft studies
• Flux measurements
• Same requirements for measurement of
  semi-volatile organic species in particles via
  thermal desorption

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Proton Transfer Reaction Mass Spectrometry
(PTR-MS) Basics
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Current PTR-MS Characteristics

• Soft ionization, little fragmentation simpler
  mass spectrum
• Selective only species with proton affinity gt
  H20 detected
• Sensitive 100 ppt for a single species with .5
  sec time resolution
• Linear over 4-5 orders of magnitude
• Concentrations can be calculated to 20-30 based
  on kinetics
• Stable over long periods infrequent calibration

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Aromatics in Mexico City 2003
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Flux Measurements in Mexico City- Methanol,
Acetone, Toluene, C2-Benzenes
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Shortcomings of Existing PTR-MS for Current ASP
Focus

• Time response limited by duty cycle of linear
  quadrupole mass spectrometer
• Background due to chemical noise, memory in
  permeable components (o-rings)
• Counts limited by interface
• Fragmentation of water clusters in interface
  affects quantification
• Speciation can be problematic - isobaric
  interferences

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PTR-ITMS Solution
Reduce chemical noise by eliminating permeable
materials allow heating
Improve interface to increase ion transmission
and reduce fragmentation
Ion trap mass spectrometer to improve duty
cycle MS-MS for identification of isobaric
species Can also perform ionization in ion trap
using drift tube to synthesize specific CI agents
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Preliminary PTR-ITMS Data
MVK
MACR
Sensitivity 100 ppb
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Progress to Date

• Leveraged off previous work with PTR-ITMS
• Electronics and software package well underway

Whats Ahead?

• Design of PTR-ITMS, particularly interface
  understand fragmentation using quadrupole PTR-MS
• Construction of PTR-ITMS
• Laboratory testing and Validation
• Laboratory studies of SOA formation in
  conjunction with AMS
• Deployment in Mexico City in 2006 by leveraging
  with EMSL funds

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Another Possibility

• May get capital funding to purchase TOF mass
  spectrometer (thanks to Carl Berkowitz)
• Could be used alone or in conjunction with ion
  trap mass spectrometer
• Modular construction take advantage of
  improvements in drift tube and interface

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Acknowledgements

• Department of Energy Energy Efficiency Program
• ORNL National Transportation Research Center and
  Staff
• Aerodyne Research Staff
• Jose Jimenez and group at U. of Colorado
• Davidovitz group at Boston College