In Situ Mass Spectrometry: Underwater Measurements

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In Situ Mass SpectrometryUnderwater
Measurements Miniaturization

• R. Timothy Short, Strawn K. Toler,
• Friso H.W. van Amerom, Ashish Chaudhary,
• Peter G. Wenner, Ryan J. Bell,
• L. Diego Miranda and Robert H. Byrne
• SRI St. Petersburg
• University of South Florida
• College of Marine Science
• AUV Science in Extreme Environments

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In Situ Mass Spectrometer Activitiesat USF SRI
St. Petersburg

• Underwater Membrane Inlet MS
• Variety of Deployments
• Cylindrical Ion Trap MS
• Extreme Miniaturization

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MS Versatile Chemical Sensor

• Trace Elements
• Isotope Ratios
• Pollutants/VOCs
• Dissolved Gases
• Proteins/Amino Acids
• Bacterial Signatures

No configuration valid for all analytes
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Membrane Inlet Mass Spectrometry (MIMS)
Ion source Electron impact
Mass-filter Quadrupole
Detector Electron multplier
Membrane
e-


Ion and fragments
Mass-scan
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Principle Features of UMS
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New 200 amu In Situ Mass Spectrometer
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Simultaneous Detection of Multiple Analytes

• Dissolved Gases
• e.g. Nitrogen, Oxygen, Argon, Carbon Dioxide,
  Methane, Hydrogen Sulfide
• Volatile Organic Compounds
• e.g. Toluene, Benzene, Dimethyl Sulfide,
  Chloroform
• Larger MW Compounds with Modification
• e.g. PCBs, Pesticides, Drugs, Toxins

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Calibration - Instrument Parameters

• Physical parameters that affect instrument
  response
• Detector settings
• Filament settings
• Residual gas
• Membrane geometry
• Membrane temperature
• Sample velocity
• Hydrostatic pressure

Constant during deployment
Variable during deployment
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Calibration - Method

• Two solutions with known gas concentrations are
  mixed at various ratios to allow for intermediate
  concentrations and in situ automated calibration

• Shipboard apparatus allows in-field sample
  preparation and calibration

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Calibration - Screenshot
Nitrogen (m/z 28)
Oxygen (m/z 32)
Methane (m/z 15)
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Deployment Methods
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Lake Maggiore Chemical Surveys

• Mass spectrometer deployed aboard an unmanned
  surface vehicle
• Mapping variation of dissolved gas ion
  intensities
• Develop surface contour maps based on gas ion
  intensity data
• Carbon dioxide oxygen data displayed

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Lake Maggiore, St Petersburg, FL
O2 and CO2 are inversely correlated in areas of
active photosynthesis and respiration
m/z 32 - Oxygen
m/z 44 - Carbon Dioxide
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Depth Profiles of Dissolved Gases

• Vertical profiles of dissolved gases with
  underwater mass spectrometer in Gulf of Mexico
• Mount instrument on custom frame along with CTD,
  DO and pH Sensors
• Communicate with instrument through standard
  UNOLS CTD tether using Seabird Modem
• Determine dissolved gas concentrations from mass
  spec data with the aid of a portable calibration
  unit

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Pre-Deployment Calibration
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Depth Profile Data (MC118)
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Future Plans for Underwater MS

• Deployment Opportunities
• Methane Hydrates Gulf of Mexico
• Subglacial Antarctic Lake Environments
• AUV in Extreme Environments?
• Alternative Sampling Interfaces
• Wider range of analytes
• Unattended Operation/ Full Ocean Depths
• Ocean Observatories
• Extreme MS Miniaturization
• MEMS Microfabrication

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Miniaturization of Ion Trap Mass Spectrometers

• Hyperbolic Electrodes
• Quadrupole Potential
• Mass Instability Scan

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Cylindrical Ion Trap MS Arrays
Hyperbolic Surfaces

• Cylindrical Geometry?Miniaturize
• Microtrap ? Lower Sensitivity
• Array ? Increased Sensitivity
• Microfab ? Tolerances

Cylindrical Surfaces
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Advantages of Miniaturizationof Mass Analyzer

• Lower voltages/lower power
• Reduced vacuum requirements
• Overall system reduction
• Reduced cost
• MS sensor networks

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Microfabricated CIT Arrays (MEMS)
Silicon Wafer
Process flow
Cylindrical ion trap
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SEM of Half-Array of Micro-Cylindrical Ion Traps
in Silicon
Fabricated CIT Half-Ring Electrodes with Endplates
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Packaging Method for Micro-CITs
6 x 6 Micro-CIT Array
Gold plated PCB for mounting and electrical
connections
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Spectrum of TCE recorded with micro Cylindrical
Ion Trap (ro 360 microns)
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Miniaturization and Integration of Peripherals
GC column
Pump
Inlet system
Detector
Ionization source
Volume of vacuum chamber, overall size and power
consumption drastically reduced
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Future Plans for Micro MS

• Optimize performance of micro-CIT array
• Optimize and integrate ion source arrays
• Fabrication and integration of other components
• Detectors
• Vacuum and sampling systems
• Pre-separation stage (e.g., GC)
• Handheld MS sensor
• Merge with Underwater MS program

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Acknowledgements

• Faculty, staff and students at the USF Center for
  Ocean Technology and College of Marine Science
• Staff at USF MEMS Facility
• Funding from U.S. Office of Naval Research (ONR)
  Grant No. N00014-03-1-0479 and U.S. Army Space
  and Missile Defense Command (SMDC) Grant No.
  DASG60-00-C-0089.

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