School of Engineering and Science - Jacobs University

the concentration of the major element being considered, since as concentrations
increase (e.g., to 500 mg/kg) the high TDS content of the solution begins to suppress
analyte intensities, similar to that observed for rock samples that are only minimally
diluted before analysis.
The quantification of the observed interferences as concentrations in mg/kg
allows predictions to be made regarding the potential impact these interferences might
have upon trace metal determinations. For example, as the CaO content in a carbonate
rock increases from 10% to 40%, then Ni concentrations determined in an HCl acid
matrix would be expected to increase from ~2.5 mg/kg to ~6 mg/kg, due to Ca
interferences on 60 Ni (Fig. A2.1). These calculated interferences in concentration
units of m/kg are obtained from the long term average instrument response as
determined from the 10 μg/kg calibration standard (described in Fig. 2, Section 4).
For example, the 60 Ni isotope has an average instrument response of 2158 cps/μg·kg -1
in 0.5 M HCl, and a sample containing 14% CaO and diluted 1000x would be
expected to generate an CaO(H) interference of ~6700 cps on mass 60. Therefore, Ni
quantified in this sample using measurement of the 60 Ni isotope would be erroneously
overestimated by approximately 3.1 μg/kg (i.e., 2158/6700 = 3.1).
It should be noted that, similar to estimates of interferences based upon raw
data (cps), interference estimates reported as concentrations (mg/kg) will vary with
instrument performance. As the long term average instrument response for the 10
μg/kg calibration standard varies by as much as 30% (RSD), and this is the basis for
the calculation of the interference magnitude in mg/kg, then these calculated
concentrations will vary similarly.
Data for interferences are presented for the following isotopes in the order;
60 Ni, 62 Ni, 88 Sr, 89 Y, 90 Zr, 91 Zr, 93 Nb, and 95 Mo. Regardless of the element of interest,
or the specific interferences that inhibit accurate concentration measurements of these
elements, the key factor is always the relative abundance of the interfering species to
the isotope of interest. In other words, the greatest analytical difficulties arise when
trying to quantify small concentrations of an element in the presence of large
concentrations of interfering elements. As a result, while some interferences may be
large, e.g., several mg/kg in the case of Ca 2 and ArCa on Sr, the effect of these
interferences is minor if the element being measured is abundant in the sample (e.g.,
115 mg/kg Sr in the JDo-1 dolomite).
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