Abraham, K.

André, L.

Cardinal, D.

Cavagna, A.-J.

de Jong, J.

Fripiat, F.

Opfergelt, S.

Planchon, F.

Open Marine Archive

Geophysical Research Abstracts, Vol. 9, 08363, 2007
SRef-ID: 1607-7962/gra/EGU2007-A-08363
© European Geosciences Union 2007
Solving interference on 30Si with a Nu Plasma
MC-ICP-MS
K. Abraham (1,2), S. Opfergelt (1,3), A-J. Cavagna (1,4), F. Planchon (1), F. Fripiat
(1, 5), L. André (1), J. de Jong (5), D. Cardinal (1)
1 Musée Royal de l’Afrique Centrale, Chaussée de Louvain 13, B 3080 Tervuren 2 Institut für
Geowissenschaften, Universität Mainz, Becherweg 21, D 55099 Mainz 3 Université catholique
de Louvain, Unité Sciences du sol, Place Croix du Sud 2/10, B 1348 Louvain-la-Neuve 4 Vrije
Universiteit Brussel, Pleinlaan 2, B 1050 Bruxelles 5 Université Libre de Bruxelles, Avenue
F.D. Roosevelt 50, B 1050 Bruxelles
Both silicon isotope ratios (δ29Si, δ30Si)1,2 can now be measured to very high pre-
cision using the High-resolution 1700 Nu Plasma or pseudo-high-resolution Finnigan
Neptune MC-ICP-MS instruments while the standard Nu Plasma instrument was lim-
ited to δ29Si determinations3 due to unresolved interferences on the 30Si peak. Poten-
tial molecular mass interferences are 14N2 and 12C16O for the 28Si peak, 12C1H16O,
N2 and 14N12H for the 29Si and 14N16O for the 30Si peak. For the first time we have car-
ried out δ30Si measurements on silica reference material on a Nu Plasma? instrument
operating in dry plasma mode and pseudo-high-resolution. The new configuration in-
volves: (1) a new designed entrance slit fixed at medium resolution (0.05 mm); (2) a
more efficient vacuum rotary pump (Big 80) and (3) two adjustable and interconnected
collector slits put in front of Faraday cups receiving the m/z 28 and 30 respectively.
With those upgrades, we can now efficiently separate the slightly heavier polyatomic
interference from the single 30Si ion applying a medium resolution (m/∆m∼1200)
on the entrance slit and tight collector slits. Tuning the collector slits at their highest
resolution results in a loss of plateau on the peaks and prevents accurate Si isotopes
measurements. However, with an intermediate setting of these slits, the new pump
helps maintaining an excellent peak plateau and the 14N2 and 14N16O interferences
are sufficiently separated from 28Si and 30Si respectively to produce reliable and accu-
rate δ30Si on reference materials (diatomite and Big Batch). Moreover, thanks to the
Big80, this new configuration does not result in a large sensitivity loss when compared
to low resolution.
At such resolution, for the standard Diatomite, we achieved preliminary results of
+0.64 per mil and +1.25 per mil for δ29Si and δ30Si respectively with a δ30Si/δ29Si
of 1.94. The values are consistent with recommended values for this recently inter-
calibrated standard (0.64 per mil and 1.26 per mil respectively)4. For the Big Batch
standard, we obtained preliminary results of –5.37 per mil (δ29Si) and –10.60 per mil
(δ30Si) which also fit to the recommended values (-5.35 per mil and –10.48 per mil)4.
Considering that mass fractionations for δ30Si are twice larger than for δ29Si, this an-
alytical improvement will enable us to better constrain tiny natural isotopic fraction-
ations recently discovered within cherts5,6, altered basalts5, igneous rocks2, soils7,
silcrete8 and plants9. From this, we expect to improve our understanding of terrestrial
silicon cycle.
1. Reynolds et al. (2006) JAAS, 21, 266-269
2. Van den Boorn et al. (2006) JAAS, 21, 734-742
3. Cardinal et al. (2003) JAAS, 18, 213-218
4. Reynolds et al. (2007) JAAS, in press.
5. André et al. (2006) EPSL, 245, 162-173
6. Robert & Chaussidon (2006) Nature, 443, 969-972
7. Ziegler et al. (2005) GCA, 19, 4597-4610
8. Basile-Doelsch et al. (2005) Nature, 433, 399-402
9. Opfergelt et al. (2006) Plant and soil, 285, 333-345


Solving interference on <sup>30</sup>Si with a Nu Plasma MC-ICP-MS

Solving interference on <sup>30</sup>Si with a Nu Plasma MC-ICP-MS

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