AN ELECTROSTATIC ION
TRAP FOR FOURIER
TRANSFORM MASS
SPECTROMETRY
Matt Lappin
OVERVIEW
•
Motivation and background
•
Fourier transform mass spectrometry
•
Electrostatic harmonic potential ion trap
•
Design and functionality
•
Simulation
•
Electronics and peripheral systems
MOTIVATION
•
Saturn’s moon Titan has interesting properties
•
Methane cycle akin to Earth’s water cycle
•
Organonitrogen rich atmosphere and organic “sand” on
the surface
•
Electrostatic discharge during rare sandstorms could
provide activation energy for a reaction to produce a
basic amino acid
Titan
MOTIVATION
•
Voyager and Cassini missions successful in probing Titan
•
Simulations of Titan’s atmosphere indicate that there is the
potential for life
•
Many mission proposals to visit Titan in the coming decade
to search for life, and a critical instrument to include would
be a mass spectrometer
MOTIVATION
•
Space bound mass spectrometer must be:
•
Small
•
Low power
•
Precise over the desired mass range of 1-300 amu, as this is
where the chemicals necessary for life will be found
•
The electrostatic ion trap mass spectrometer proposed here
meets these requirements
OVERVIEW
•
Motivation and background
•
Fourier transform mass spectrometry
•
Electrostatic harmonic potential ion trap
•
Design and functionality
•
Simulation
•
Electronics and peripheral systems
FOURIER TRANSFORM MS
• Mass spectrometry involves ionizing a compound and measuring
the abundance of ions produced at each mass level
• FTMS detects oscillation in the time domain of these ions and
converts the time domain signal into a frequency spectrum
• Oscillation is engineered so that the frequency is related to the
mass to charge ratio
FOURIER TRANSFORM MS
• Magnetic field of strength B causes oscillation of ions with frequency
w = qB/m
• Detection plates provide time domain signal
• Fourier transform provides frequency spectrum, which is proportional
to mass spectrum
FOURIER TRANSFORM MS
RF Sweep to
Accelerate
the Ions
Transient Ion
Image
Current Signal
Mass
Spectrum
Most mass
spectrometers detect
ions (destructively)
using an electron
multiplier. ICR
detects ions from
their image charge
ORBITRAP
●
Electrostatic
●
Complicated ion injection
●
Tranverse oscillation
frequency related to m/z
OVERVIEW
•
Motivation and background
•
Fourier transform mass spectrometry
•
Electrostatic harmonic potential ion trap
•
Design and functionality
•
Simulation
•
Electronics and peripheral systems
THE AUTORESONANT ION TRAP MS
●
A.V. Ermakov and B.J. Hinch of Rutgers used a similar trap in
their autoresonant ion trap mass spectrometer (ART-MS)
●
Verified f is proportional to 1/(m/z)½ for ions in the mass range
1-300 Da
●
ART-MS uses resonant ejection, not FT-MS, which requires RF
sweep
Ermakov, A.V.; Hinch, B.J. An autoresonant ion trap mass spectrometer. Rev. Sci. Instrum. 81,
013107 (2010); doi: 10.1063/1.3276686
THE ELECTROSTATIC HARMONIC
POTENTIAL ION TRAP
3A current
source
Plate to protect
macor filament clamp
(0V)
1 kV, switched
The trap is 2.5”
long and has a
1” diameter.
Can be pulsed to
10V
Held at a
positive
potential
(5V)
To detector (0V) for
image current detection
ION PRODUCTION AND ANALYSIS
5V
0V
ION PRODUCTION AND ANALYSIS
5V
0V
ION PRODUCTION AND ANALYSIS
1000 V
0V
SIMION SIMULATION PARAMETERS
●
●
●
Pulse time: 5 microseconds
Trapping potential delay: 17 microseconds
Trapping duration: 1 millisecond
Scientific Instrument Services, Inc., Ringoes, NJ, www.simion.com
VACUUM CHAMBER/FLANGE
10-pin instrumentation
BNC
SHV
CONSTRUCTION
Source
Signal plate
Trap
Trapping plates(1kV)
●
Stainless steel plates and alumina tubes/spacers: Kimball Physics eV parts
●
Assembled by Caltech CCE Insturment Shop
ELECTRONICS
Vacuum
ELECTRONICS
SIGNAL DETECTION CIRCUITS
Image Credit: Amptek, Inc.
Image Charge Detection Mass Spectrometry: Pushing the Envelope
with Sensitivity and Accuracy. John W. Smith, Elizabeth E. Siegel,
Joshua T. Maze, and Martin F. Jarrold. Analytical Chemistry 2011 83
(3), 950-956
SUMMARY AND CONCLUSIONS
●
Verified that the instrument should work based on SIMION
simulation
●
Instrument assembly is in progress
●
Tests to come after the completion of assembly
ACKNOWLEDGMENTS
I would like to thank all members of the Beauchamp group,
especially Professor Beauchamp and graduate student Daniel
Thomas, for all of your help. I would also like to thank Jeff
Groseth in the CCE Electronics shop for helping with the
assembling the electronics for the spectrometer, and the CCE
Machine shop for help with machining and assembling parts of
the instrument.