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IsoProbe
is a new generation isotope ratio mass spectrometer.
This instrument
combines the ionisation efficiency
of an inductively coupled plasma with the
advantages
of multi-collector data acquisition.
Simultaneous
measurement of each isotope has the benefit
of eliminating time-related instabilities in the ion beam generated
by plasma ionisation, providing precision
on isotope ratios equivalent to TIMS.
The plasma source efficiently generates ions from most elements, enabling
simultaneous inter-element isotope ratio determination. As with ICP-MS,
sample introduction can be
in the form of a solution, or via laser ablation. Instrument sensitivity
in solution mode is such that highly precise isotope ratios (<0.001%
2s.e.) can be achieved on solutions with concentrations <50ppb. Multi-collection
of isotopes has great advantages for laser ablation of individual mineral
grains or solids as it effectively eliminates imprecision caused by
transient and unstable ablation signals. The collector
arrangement on the IsoProbe permits the simultaneous measurement of
the isotopes of Hg, Pb, Th and U (a spread of 36 mass units). Using
the ion counting Daly detector in conjunction with the WARP filte r
enables isotope ratios to be measured in solutions with 0.5 ppt with
a precision better than 0.2% 2sd reproducibility. Hence the instrument
is suitable for measuring plutonium isotope ratios in environmental
samples.
Uranium isotope ratios can be measured with high precision and accuracy.
238U/235U can be measured to better than 0.08%
(2sd) on natural ratios on 5ng of uranium.
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