School of Engineering and Science - Jacobs University

Potential interferences on monoisotopic 93 Nb are presented in Fig. A2.10, and
are very similar to those described for 91 Zr. This is due to the substitution of the 37 Cl
isotope for 35 Cl in the Fe and Ca molecular species listed above (i.e., 56 Fe 37 Cl and
40 Ca 16 O 37 Cl). Unlike Zr, Nb offers no additional isotope for analysis, and the low
natural abundance of Nb exacerbates the problem of interfering species due to major
elements. Accurate Nb analyses are unlikely in Fe- and Ca-rich rock types, unless the
use of HCl is avoided. However, as discussed in Section 7.1 of the main text, Nb is
unstable in pure HNO 3 acid matrices, and the presence of HCl stabilizes Nb, as well
as other HFSE like Ta, in solution long enough for accurate ICPMS measurements.
As mentioned previously, future work examining the optimum acid matrix for ICPMS
determinations of Nb and Ta is recommended.
The last element that appears to suffer from major element interferences is
Mo, and in particular Mn interferences on the 95 Mo isotope (Fig. A2.11). Similarly to
the Ca-Ar interferences on 88 Sr, Mn affects measured intensities for 95 Mo regardless
of the acid matrix. This is apparently due to the 55 Mn 40 Ar molecular species, which
forms independently of the bulk solution composition. Whereas the use of HCl
appears to suppress 55 Mn 40 Ar formation (Fig. A2.11), the magnitude of the
interference is significant regardless of the acid matrix (e.g., ~3-6 mg/kg at 20-30%
MnO). It is therefore recommended that the 97 Mo isotope be used for Mo
determinations in rock samples that contain more than a few percent MnO, unless Mo
concentrations in the sample are the range of 50 to hundreds of mg/kg.
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