So this is a thermal ionization mass spectrometer.
It's made by Thermo Finnigan.
It's called a Triton.
It's a state-of-the-art mass spectrometer that allows us
to do isotopic analyses when the samples have been loaded
on filaments.
It can be run in both positive ion and negative ion mode.
And we use it in negative ion mode
to analyze osmium on a wide range of samples from xenoliths
of the mantle lithosphere all the way down
to these tiny inclusions of sulfide
that we have isolated, separated, and brought down
from the chemistry lab.
Each sample gets loaded on one filament,
and then you can put 21 filaments
in this mass spectrometer.
It can be run on automatic.
We can often run it from an iPad from our offices
or from home, which is pretty handy.
When we're running a small sample like a sulfide,
the osmium signal is very small, and so we
do single ion counting.
That's where our absolute limit is.
We often count hundreds of thousands of counts per second,
but we use a method called pulse counting, which
can detect individual ions, each individual ion arrival that
happens.
The way these instruments work is that they have a magnet.
You can see the magnet at the bend in the mass spectrometer
here, the white unit.
And there's an evacuated tube called a flight tube.
And the samples are ionized on the filament.
They make a negative molecular species
of osmium trioxide, OSO3 minus.
And that is accelerated through the flight tube,
the magnet separates the osmium into the isotopes
of osmium, which are then detected in the detector
region of the mass spectrometer over here.
If we ran a big osmium isotope beam,
we have multiple Faraday cups, which can detect the larger
signal, and we would run all the isotopes of osmium
into different detectors at one time.
But we only have one electron multiplier
in this mass spectrometer, and so we
have to sequentially switch the isotope beams of osmium
into the single detector by changing the magnetic field.
And that's called magnifield switching, or single detection
isotope ratio measurement.
And the reason we confine osmium to this instrument
is that we get less cross-contamination
of our sample.
It's much more sensitive for osmium,
so this is ideally suited for osmium.
We tried to do osmium in one of the other mass spectrometers
by inductively coupled plasma mass spectrometry.
Those mass spectrometers tend to have
a lot of cross-contamination between samples.
We know if there's rhenium in this instrument
because this instrument's used for a lot of different types
of measurements, a wide range of isotopic measurements.
And many of those measurements are run on rhenium filaments.
And so once we're running rhenium filaments
in the instrument, the background for rhenium
is so high that we can't run low-level rheniums
without cross-contamination.
So we can't really run rhenium over here.
These are the control screens for the Triton.
On the left, we have instrument control screens
with a variety of choice.
You select these tabs, and you can control the instrument
by dropping down the tabs and controlling
the various functions of the instrument.
None of these mass spectrometers have buttons anymore
or knobs to turn.
It's all done with computer control.
The progress of the analysis is usually shown here,
and a duplicate of the display is over here.
This is a previously-run sample, a post-doc
named Hanika who's working on very,
very ancient rocks, crustal rocks on Earth,
has run these for chrome, and this
is the progress of the analysis.
These are individual ratio measurements
taken over a period of hours shown on the display here.
And typically, these mass spectrometers,
they produce a lot of data, which is shown in the columns
here.
Any isotope ratios are here in the beige color summary
averages.
These are the individual ratio measurements in columns.
This is very typical of how data comes off
this mass spectrometer.