School of Engineering and Science - Jacobs University

‘loss’ of these elements in dissolved rock solutions due to adsorption/precipitation
reactions in sample containers (Münker, 1998). For trace concentrations of Nb and
Ta, Münker (1998) suggested diluting dissolved rock samples in 0.3 M HNO 3 and
0.06 M HCl for stabilizing these metals for ≥24 h, and the addition of 0.02 M HF
when Nb and Ta in the diluted solution exceeded approximately 100 μg/kg and 4
μg/kg, respectively. The consistent use of 0.5 M HCl and the formation of MCl(O) +
interferences does not appear to have adversely affected analytical precision or
accuracy for the majority of the ICPMS analyses discussed here. However, for
samples rich in Mg, Mn, and/or Fe that also have very low trace metal concentrations,
it would be useful to more fully investigate mixtures of HNO 3 and HCl in order to
maximize the sensitivity of the ICPMS method.
Some interferences persist regardless of the acid matrix used and result from
analyzing aqueous solutions (e.g., CO 2 on 45 Sc), or from sample ionization in an Ar
plasma. The latter effect is illustrated by presumed 44 Ca + 2 and 48 Ca 40 Ar + interferences
on 88 Sr, which may erroneously increase measured Sr concentrations by 1-3 mg/kg as
CaO contents in sample powders approach 40%. Another example is 55 Mn 40 Ar + ,
which produces a 2-5 mg/kg interference on 95 Mo in sample powders that contain 10-
15% MnO. Figures illustrating the significant interferences observed for Ni, Sr, Y, Zr,
Nb, and Mo are presented in Appendix 2, and permit estimates of the magnitude of
these interferences in various rock samples. It should be stated, however, that
interferences observed in this study may not significantly affect analytical accuracy,
provided the magnitude of the interference is small relative to the concentration of the
trace metal of interest. An example is Nb, which cannot be determined accurately in
Fe-rich, Nb-poor samples (20 mg/kg Nb).
Analytical accuracy, as defined by the agreement between the average
reference value and the measured JUB concentrations (App. 1), is presented in the
following figures as a ratio of (JUB data/reference value), with a ratio of one
indicating perfect agreement between the JUB data and the average CRM reference
value. However, significant uncertainties in reference values exist for some elements,
and some CRMs are more poorly characterized than others. This uncertainty in the
CRM reference values can produce a wide range in the calculated ratio of (JUB
data/reference value). Therefore, the range in calculated ratios due solely to reference
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