Title: Proton Transfer Reaction Ion Trap Mass Spectrometer PTRITMS: Next Generation Aircraft Instrumentatio
1Proton 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
2Motivations 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
3Proton Transfer Reaction Mass Spectrometry
(PTR-MS) Basics
4Current 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
5Aromatics in Mexico City 2003
6Flux Measurements in Mexico City- Methanol,
Acetone, Toluene, C2-Benzenes
7Shortcomings 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
8PTR-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
9Preliminary PTR-ITMS Data
MVK
MACR
Sensitivity 100 ppb
10Progress 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 -
11Another 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
12Acknowledgements
- 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