High Resolution Mass Spectrometry In Space

Exploration:Past Triumphs, Present Goals,

Future ProgressRob 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 Weight1 grain (= 64.79891 mg) with 7000 = 1 pound 16 grains = 1 “gram” = 1.03678256 g 27.34375 grains = 1 dram ( 1.771 g) 16 dram = 1 ounce ( 28.35 g)16 ounces = 1 pound ( 453.59 g )14 pounds = 1 stone ( 6.3503 kg) 2 stones = 1 British quarter ( 12.701 kg) But US quarter = 25 pounds ( 11.34 kg)hundredweight or cwt. =

4 British quarters =112 pounds ( 50.80 kg) 4 US quarters =100 pounds (= 45.35 kg)

20 hundredweights = 1 ton, British long ton (= 2240 lb or 1016.04 kg) US short ton (= 2000 lb or 907.18 kg)

•1 block = 5 lbs •1 head = 6 3/4 lbs •1 clove or brick = 7 lbs •1 quartern = 4 lbs •1 gallon = 10 lbs•1 score = 20 lbs •1 truss (straw) = 36 lbs •1 frail = 50 lbs •1 firkin = 56 lbs or 2 quarters •1 bushel = 63 lbs •1 tub = 84 lbs •1 box = 90 lbs •1 fagot or seam = 120 lbs•1 sack = 168 lbs•1 wey = 182 lbs

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 pendulum clock, ~ 0.1s/10s = 1‰

West Point~1900

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 GloryAvogadro’s number (actually due to Austrian JosefLoschmidt 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 'pulling their legs.'"

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, 1856-1940

Thomson ParabolaE // 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)

University of Bonn

Federal Republic of Germany

1913--1993

University of Washington, Seattle

b. 1922(in Görlitz, Germany)

•for the development of the ion trap technique

Dynamic Force Measurement ()Static electric field produces a quadratic restoring force 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.

ADD coaxial B-field to stabilize. Resonant frequency mass

Penning Trap (FT-ICR MS)

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 MeasurementThe 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]³2) 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 Langmuir

~1910

Becquerel

1897

Energy eV – keV 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 ~kg 10-100kg

Power ~5-10W 100-1000 W

Size <50cm 1-10 m

Robust 1g 10g @100Hz

MTBF Years hours

UV 100Mcts/s 1ct/s

Source Temp 1-100 keV 0.001 keV

Energy width 100% .01-1%

Radiation 10-100kRad/y <1 kRad/y

SW/Plasma MS Timeline

Mass Spectrometer Year, Mission Resolution

Ion Traps 1959 Luna 1 < 2

Faraday Cup 1961 Explorer 10 ~2

Electrostatic E/Q 1962 Mariner 2 ~3

Wien Filter 1983 ISEE-3 ~5

Magnetic Sector 71 Apollo*, 86 Giotto* >40, >10

Linear TOF 1984 Ampte ~15

Isochronous TOF 1996 Wind ~100

Reflectron TOF 2004 Rosetta* >3000

Helical TOF 20?? >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 proto-solar 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

WireCombGate

HyperbolicReflector

AnnularMCP &Detector

CollimatorIons

Ions

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.