1. Isotope Ratio Mass Spectrometers (IRMS)
Ionization
►Make the Ions
Deflection
►Separate the Ions
Detection
►Count the Ions

2. Isotope Ratio Mass Spectrometers (IRMS)
Next, the ions are accelerated
toward an electromagnet
through the flight tube.
The electromagnet
deflects the ions.
Electromagnet
Flight Tube
Gas
Ion+
Ion Source
First, gas molecules
are turned into ions
in the ion source.
1H2
‘Light’ ions are deflected
further than ‘heavy’ ions. DH
lighter ions
heavier ions
Carbon Dioxide (CO2)
12C16O M (mass 44)
13C16O M+1 (mass 45)
12C18O16O M+2 (mass 46)
Carbon Dioxide (CO2)
12C16O M (mass 44)
13C16O M+1 (mass 45)
12C17O16O M+1 (mass 45)
12C18O16O M+2 (mass 46)
M+2
M+1 M
Finally, detectors
count the number
of ions for each mass.
Detectors

3. Ionization – Electron Impact Source
Electron Trap
Magnet compresses
electron beam N S
Electrostatic Lenses e e
Gas Inlet e
Ionization Efficiency
1 ion / 1000 gas molecules
Gas
Ion+
Ion+
Ion+
Ionization
Chamber e e e e e e e
Magnet compresses
electron beam N S
Cathode
Extraction
X-Focus
Slit
X-Deflection
Y-Deflection
Electron Source
Form
Ion Beam
Focus Ions
on the Slit
Guide Ions Toward Detectors.

4. Take a Deep Breath… Here Comes Some Heavy Lifting

5. Ion Deflection: The Math
Ions are ejected from the ion source
by an accelerating electric field (V)
Ep = zV = 1/2 mv2 = Ek
Ep = potential energy
Ek = kinetic energy
m = ion mass
z = ion charge
V = electric field potential
v = ion velocity
As the ions pass through magnetic field (B) the ions are forced to follow a circular path of radius (r)
(Lorentz force law).
Fc = mv2/r = zvB = FB
Fc = centripetal force
FB = magnetic force m B2 2V z =
Ion Mass
Acceleration
Potential
Magnetic
Field
Ion
Charge
Radius r2
Ion Source
Electromagnet z m
= k r2
Solving for v: v = [2zV/m]1/2
This equation shows that if B and V are held constant, ions of different mass-to-charge (m/z) will follow circular pathways of different radii (r)
Combine the two equations
Solving for v: v = zrB/m

6. m z Ion Deflection: Electromagnet
(The Right Hand Rule – Positive Charge) v F v B
(out of screen)
Magnetic Field (B)
(coming out of the screen)
Heavy Ion v F B
Velocity
Vector (v)
Force (F)
Magnetic Vector (B)
Light Ion F z m
= k r2 F F
Note: Force F is perpendicular
to both the velocity vector (v)
and the magnetic field vector (B).

7. Ion Detection: Faraday Cup Array
Mass+2
Mass
Mass+1
ion beam
ion beam
Cup 4
ion beam
Cup 3
Cup 2

8. Ion Detection: Faraday Cup
Collector Slit
Faraday Cup
Ion Count + _
Ion+
Ion+
Ion+ e- e- e- e-
Ion+ 1 2 3 4
Ion
Beam
Electron
Source
Ground
Secondary Electron
Suppression Shield

9. Isotope Ratio Infrared Spectroscopy (IRIS)
Bend
► Lasers and Mirrors
Symmetric Stretch
Asymmetric Stretch

10. Isotope Ratio Infrared Spectroscopy (IRIS)
Infrared Absorption Spectra of 12C16O2
Mid-infrared absorption lines of a subset of the isotopologues of CO2.
Waechter 2007

11. Isotope Ratio Infrared Spectroscopy (IRIS)
Tunable Diode
Laser
H2O
H2O
Mirror
H2O
H2O
Syringe
Mirror
H2O
H2O
H2O
H2O
H2O
H2O
H2O
Water
Photodetector
Sample
Inlet
Sample
Outlet
100
Time
H2O
Empty %
H2O
Vaporizer