School of Engineering and Science - Jacobs University

The second blank contribution to ICPMS analyses is the method blank. The
method blank is a solution that has been processed in exactly the same manner as a
sample during the decomposition method, and represents the contamination added to
a sample as a result of the decomposition method and subsequent dilution in acid.
While significant amounts of concentrated acid are used in the decomposition
methods, these acids (in combination with contamination from labware) contribute
insignificant amounts of trace metals to rocks typically analyzed, even for trace
metal-poor samples like iron-formations and dolomites (Fig. 4). Method blank values
are determined for every ICPMS analysis to monitor possible contamination sources,
but as a result of the above observations, ICPMS data are blank corrected by
subtracting the acid blank intensities. Only in instances where method blank values
are significantly higher than those observed in Fig. 4 are blank corrections performed
using the method blank intensities. The reasoning for this approach is as follows;
since the method blanks are typically below the IQLs determined from the acid
blanks, the method blank is not quantifiable. Only when method blanks exceed the
acid blank IQL are they used for the blank correction. It should be noted that with
regard to the carbonate decomposition method, many refractory elements (e.g., Ti,
Nb, Ta) are not suitable for quantification, as they are expected to be primarily hosted
in silicate-bearing phases that are resistant to dissolution with nitric acid, and in
particular the poor IQLs for Sc mean that it is generally not quantifiable in trace
metal-poor samples regardless of the decomposition method used (Fig. 4).
5. Analytical precision
For the analyses conducted within the Geochemistry Lab at JUB, analytical
precision may be defined in different ways. The highest degree of precision is
expected when considering only the 60 mass scans performed during ICPMS analysis
of a single sample solution. If this sample solution is periodically re-measured with
time during an ICPMS run, i.e., by occasionally returning the autosampler probe to
the vial containing the solution, then analytical precision would be expected to
decrease. Further decreases in analytical precision should occur if one considers
repeated analyses of the same sample solution on different days, or repeated acid
decompositions of the same sample powder, with the decreasing precision reflecting
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