Transcript High Resolution Mass Spectrometry In Space Exploration: Past Triumphs, Present Goals, Future Progress Rob Sheldon NSSTC July 30, 2004

High Resolution Mass
Spectrometry In Space
Exploration:
Past Triumphs, Present Goals,
Future Progress
Rob Sheldon
NSSTC
July 30, 2004
Outline
• What is Mass Spectroscopy?
– Weighing atoms, molecules, viruses…
• The Art of Weighing
• A Short History with Nobel Prizes
• An Even Shorter History of Space Mass
Spectrometers
• HELIX
What is Mass Spectroscopy?
The Art of Weighing
Why Weigh? or How Weigh?
• Why?
– Quantity: Economics is established on this.
– Quality: e.g. Identity. (Archimedes eureka story)
• How?
– Gravitational force (static):
• Directly = spring balance (susceptible to external noise)
• Comparatively = pan balance (common mode rejection)
– Inertial forces (dynamic, e.g. space station scales)
• Resonant frequency (copper pennies, ripe watermelons)
• Hefting (selecting hammers)
Galileo showed they were the same “mass”, so
physics students are taught to never say “weight”
English Units of Weight
•1 block = 5 lbs
1 grain (= 64.79891 mg) with 7000 = 1 pound •1 head = 6 3/4 lbs
16 grains = 1 “gram” = 1.03678256 g
•1 clove or brick = 7 lbs
27.34375 grains = 1 dram ( 1.771 g)
•1 quartern = 4 lbs
•1 gallon = 10 lbs
16 dram = 1 ounce ( 28.35 g)
•1 score = 20 lbs
16 ounces = 1 pound ( 453.59 g )
•1 truss (straw) = 36 lbs
14 pounds = 1 stone ( 6.3503 kg)
•1 frail = 50 lbs
2 stones = 1 British quarter ( 12.701 kg)
•1 firkin = 56 lbs or 2
But US quarter = 25 pounds ( 11.34 kg)
quarters
hundredweight or cwt. =
•1 bushel = 63 lbs
4 British quarters =112 pounds ( 50.80 kg) •1 tub = 84 lbs
4 US quarters =100 pounds (= 45.35 kg) •1 box = 90 lbs
•1 fagot or seam = 120 lbs
20 hundredweights = 1 ton,
British long ton (= 2240 lb or 1016.04 kg) •1 sack = 168 lbs
•1 wey = 182 lbs
US short ton (= 2000 lb or 907.18 kg)
Lagrange vs.
Hamilton
• Newton is overemphasized in physics instruction.
Goldstein’s 1950 “Classical Mechanics” introduced
physicists to the importance of energy measures and their
equivalence to forces. Feynman attempted a lecture series
starting with energy conservation. Some H&R problems are
insoluble with forces, but simple with energy.
• Hamiltonian methods (vs Lagrangian integration of forces)
are used by accelerator magnet designers because they work
faster and are more accurate. (Lie algebra convergence etc)
• All our techniques of weighing used “forces”. Is there
another way to weigh using “energy” ?
Illustrated w/Heisenberg’s
Uncertainty Principle
x (mv)  h/2
Now, multiply & divide by v, e.g. v/v =1
x/v (mv)v  t E  h/2
• A force is described as a change in momentum,
(mv). So “weighing” objects with known force
requires measuring a displacement, x.
• Therefore given a known energy, E, we can “weigh”
by measuring elapsed time (time-of-flight), t .
Some Corollaries
• A “known” force need not be measured, (e.g.,
gravity) it need only remain the same during the
measurement. Relative masses (ratios) are usually
good enough.
• Displacement must always be measured. Resolution
then depends on measurement of displacement.
(mirrors, lasers etc.)
• Likewise a known energy need not be measured, but
elapsed time must be, and resolution goes with time.
• Therefore R = x/x or t/t. Which is better?
Balance vs. Atwood’s Machine
2 x/g t² = (M-m)/(M+m)
Errors in timing from
West Point~1900
pendulum clock, ~
0.1s/10s = 1‰
Accuracy of Methods
1. Spring balance, direct force measurement, rarely used in
last 3000 years. Precision depended directly on x/x ~
1%. Very noisy, accuracy affected by everything.
2. Pan balance, direct force measurement, null-configuration
(common mode rejection) enabled precision to the level of
the differential noise (air currents) Accuracy dominated by
calibration error. E.g. Biblical injunctions against separate
“selling” and “buying” weights. Guesstimate m/m <
1‰
3. Timing methods: never used. Error t/t > 1‰ with
pendulum clocks, probably >10% with ancient timers.
4. Dynamic balance, eg., frequency of pendulum: never used.
Frequency standards unknown. Multiplies the errors of
timing (#3) with the errors in length (#1). Error >10%
Weighing atoms
• Weighing atoms is hard. Pan balances can achieve
micrograms, but molecules are
micro-micro-micro-micrograms!
• It turned out that the accuracy of measurement is
exactly opposite for atoms than for apples.
– Dynamic (FTMS) has the highest accuracy, R>106
– Timing (TOFMS), R~106,
– Static (spatial) measurement (Mattauch-Herzog),
R~105.
The Weight of Glory
Avogadro’s number (actually due to Austrian Josef
Loschmidt in 1865, but renamed for a frenchman by 1926
Nobel laureate J. Perrin) predicted the weight of “atoms”.
Ernst Mach, pre-eminent mathematician, physicist, and
philosopher of the 19th century, did not believe in atoms
because he couldn’t see them. In 1905 Albert Einstein
derived Avogadro’s number from Brownian motion. All
these indirect methods, however, required macroscopic
quantities, and incurred large errors. But in 1897, though
we couldn’t see them, we could weigh them individually.
J.J. Thomson "At first there were very few who believed in the
existence of these bodies smaller than atoms. I was even told long
afterwards by a distinguished physicist who had been present at my
[1897] lecture at the Royal Institution that he thought I had been
A Short History of Mass
Spectrometer Nobel Prizes
Joseph John Thomson
(Physics 1906)
• in recognition of the great
merits of his theoretical and
experimental investigations
on the conduction of
electricity by gases"
• Cambridge University, 18561940
Thomson
Parabola
E // B,
R~10%
Francis Aston
(Chemistry 1922)
• Cambridge University 1877 - 1945
• for his discovery, by means of his
mass spectrograph, of isotopes, in a
large number of non-radioactive
elements, and for his enunciation of
the whole-number rule.
Crossed E and B
R~1%
Static Force Measurement (x)
Thomson: Demonstration, physics
Aston: Application, chemistry
Double Focussing Magnetic Sector
Aston’s contribution was to use the deflection by B to
balance E. Careful considerations led to the “double
focussing magnetic sector MS” attributed to both
Nier-Johnson and Mattauch-Herzog.
Hans Dehmelt & Wolfgang Paul
(Physics 1989)
•for the development of the ion trap technique
University of
Washington,
Seattle
University of Bonn
b. 1922
Federal Republic
(in Görlitz,
of Germany
Germany)
1913--1993
Dynamic Force Measurement ()
Static electric field produces
a quadratic restoring force
Penning Trap (FT-ICR MS) along z-axis. Hooke’s Law.
But since ²=0, (Laplace’s
eq), d²/dz ² -d ²/dr ² =0,
positive curvature in one
coordinate = negative
curvature in the other.
Convergence in z =
Divergence in r.
Resonant frequency  mass
ADD coaxial B-field to
stabilize.
The Paul Trap
RF instead of B-field. Two possibilities: 2-D
(QuadMS) and 3-D (Ion Trap MS)
How can RF replace B?
Just as the ball starts to roll
left or right, the hyperbolic
“saddle” is rotated 90
degrees, so the ball is
pushed back to the center
in x.
DUST!
John Fenn & Koichi Tanaka
(Chemistry 2002)
• for the development of methods for identification and
structure analyses of biological macromolecules
• for their development of soft desorption ionisation
methods for mass spectrometric analyses of biological
macromolecules
Virginia
Commonwealth
University
Richmond, VA
(Yale Emeritus)
1917--
Shimadzu
Corp.
Kyoto,
Japan
1959--
Ionization Methods
• We’ve completely ignored the necessity of using
ions (rather than neutral atoms) & ionization.
• Electron impact ionization E~1ev is fine for atoms
and inorganic molecules, but breaks most organic
bonds, fragmenting them. Gentler ionization
methods must be used for biomolecules.
• Electron, plasma, ion, atom, laser impact are rough
• Thermal, field-emission, chemical reaction better
• Protonation & Matrix assisted are easy & gentle.
Time Measurement
The Reflectron TOF MS
• A narrow pulse of nearly mono-energetic ions streams
through a drift region, where velocity-dispersion separates
masses. Timing the arrival shows mass peaks. But
Peakwidth = pulse width * dE/E.
• The solution is a mirror, that makes the more energetic ions
take a longer path, and to first order, correct dE/E
W.Stephens, W.Wiley I.McLaren
& B.Mamyrin
(Physics, 20??)
• “for the invention of time-of-flight & reflectron
MS”.
• Why am I so sure?
1) [Physics demonstration, Chemistry applied]³
2) Biochemistry applications using TOF are
becoming very compelling, and there has to be a
physics demonstration first.
3) TOF is getting better and smaller; but magnets,
quads are maxed out.
4) It is the next logical way to weigh.
An Even Shorter History of
Space MS
(Plasma vs Radiation)
Property
Plasma
Radiation
Discoverer
Energy
Langmuir
~1910
eV – keV
Becquerel
1897
MeV
Mass
Measurement
Deflection
E & B-fields
Ionization
dE/dx, emulsion
Detection
Photomultiplier,
Faraday cup
Direct ionization,
scintillation
The Challenge of Space MS
Property
Space
Lab
Weight
Power
Size
Robust
MTBF
UV
Source Temp
Energy width
Radiation
~kg
~5-10W
<50cm
1g
Years
100Mcts/s
1-100 keV
100%
10-100kRad/y
10-100kg
100-1000 W
1-10 m
10g @100Hz
hours
1ct/s
0.001 keV
.01-1%
<1 kRad/y
SW/Plasma MS Timeline
Mass Spectrometer
Ion Traps
Faraday Cup
Electrostatic E/Q
Wien Filter
Magnetic Sector
Linear TOF
Isochronous TOF
Reflectron TOF
Helical TOF
Year, Mission
1959 Luna 1
1961 Explorer 10
1962 Mariner 2
1983 ISEE-3
71 Apollo*, 86 Giotto*
1984 Ampte
1996 Wind
2004 Rosetta*
20??
Resolution
<2
~2
~3
~5
>40, >10
~15
~100
>3000
>1000
Why Bother with Composition?
• “Minor effects of minor ions” said a colleague
• The Plasma Ecosystem
– Origins: tracers
• Fast/slow solar wind; ionosphere/SW m’spheric
– Acceleration: both as tracer and trigger
• O+ changes reconnection rate;
– Transport: both tracer and differentiator
• SEP composition reveals E/q acceleration
– Death: ENA visualizations (IMAGE)
• He from SW, O from Earth
Sun-Earth Connection
• AMPTE magnetospheric data, model and
ratio, for He++, showing inability of
standard models to account for SW input
into the magnetosphere.
SW Elemental Composition
• Mass can separate
degenerate M/Q
species
• Charge states give
coronal temperatures
at different altitudes.
• Differentiate
Fast/Slow SW
• Ascertain SW origins
SW Isotopic Composition
• Isotopes can reveal
unique acceleration
in SW. 3He, 15N.
• Triple Mg isotopes
permit studies of
mass fractionation
of Solar interior.
• Origins of protosolar nebulae, age
of the sun.
Origins of Solar System
Origins of Life
• 1974-Viking lander on Mars
K. Biemann
b. Austria
1926
Origins of Universe
• 6Li is a crucial element formed in the big bang
• 10Be believed to be a tracer for cosmic ray
lifetime
• Ne22 gives information on SW processes in
Wolf-Rayet stars
• Pickup ions are interstellar neutrals that have
drifted into the heliosphere and become
charged. We learn about ISM from them.
What Does the Future Hold?
• Increase in mass resolution and sensitivity are
needed for measuring isotopes in the highly
rarified interstellar medium (ISM).
• High mass range is needed for looking for
biomarkers on Mars, Europa, Titan, comets.
• Faster data acquisition needed to see finer details
of solar wind, shocks and flybys.
• More robust, compact instruments will enable
more science on limited future opportunities.
TOF and Gating
• As the timeline shows, TOF has the most growth
potential of all the techniques so far. The major
hurdle in improving TOF Resolution (and
sensitivity, which gives better dynamic resolution) is
the width of start pulse, e.g. gating.
• Carbon foils give ns widths, but at a steep price. No
one has found a way around it, everyone has tried.
• Therefore faster electronic gates are needed AND
longer TOF. But longer TOF means bigger!?
• We solve all these problems with a helical TOF.
NSSTC TOF lab
Schematic TOF MS concept
Wire
Comb
Gate
Ions
Ions
Collimator
Annular
MCP &
Detector
Hyperbolic
Reflector
Prototype HELIX with gate
SIMION Ion Trajectories
First Data
Predictions
• NASA origins theme will not succeed w/o MS.
• Mass spectrometry will continue to produce Nobel
prizes in the 21st century.
• The trends show that MS will get smaller, more
robust, and more capable. TOF seem to be gaining
on Quads for size and portability. They also have
the edge in power consumption and sensitivity.
• HELIX is one of many solutions to making TOF
more compact. We are within a factor of 10x of
having it in a cell-phone. Now you can be smarter
than your dog.