Abstract
Operating an Agilent 7700X ICP-MS spectrometer under robust plasma conditions (1550 W) with a He-filled octopole collision cell and analysing solutions (−1 total dissolved solids) still suffered analyte peak suppression due to matrix effects. International reference rocks BCR-1, BHVO-1, AGV-1, G-2 and BCR-2 all showed count rate reductions for 36 elements (mass range 7Li to 238U) averaging ~10% but with no dependence on isotope mass. Use of an internal standard (103Rh) and/or using a ten-fold dilution of sample solutions reduced these effects but problems with reduced count rates combined with larger errors for some elements introduced other problems. The best approach was to normalise the count rates for each element in the other samples against those for BCR-1 as an external standard; thus the count suppression due to the matrix effect is corrected for each individual element. This approach provides standardization “traceability” in line with the ERM ISO/IEC requirement. Experiments are also reported on quantifying the proportions of Ba and selected REE oxide/hydroxide components versus parent isotopes (XO/X and XOH/X). This information is essential for correcting peak interferences on higher mass number REE for the rock samples, and equations are developed to use measured CeO/Ce and CeOH/Ce ratios to predict such values for any other member of the REE suite. Concentrations obtained show excellent agreement with recommended values for the international reference materials especially for the REE. Robust data are also provided for two other standard rocks: nepheline syenite STM-1 and quartz syenite CAAS-1; the latter shows exceptional enrichments of Zr, REE, Th, and U.
Highlights
In recent years Environmental and Earth Science research programmes have benefitted greatly from the application of Inductively Coupled Plasma Mass Spectrometric (ICP-MS) trace element analyses (Potts, 1987; Jenner et al, 1990; Linge & Jarvis, 1997; Makishima & Nakamura, 2006; Chauvel et al, 2010)
In analyses carried out in 2017 we attempted to avoid using an internal standard but during data-reduction we found that the ICP-MS data for solutions having dilution factors (DF) of 500 (TDS < 2000 μg·g−1) generally gave lower concentrations than those for the most reliable elements determined by XRF (e.g., Ni, Ba, Ce) and ID (e.g., Nd, Sm) for the same Marangudzi rocks while the BCR-1, BHVO-1, AGV-1, and G-2 samples normalised to the recommended concentrations for most elements gave slightly lower ratios (e.g., REE ~0.90 ± 0.05) than expected
The ultra-low detection limits for trace elements shown by ICP-MS techniques means that most geochemically important elements can be detected in almost all laboratory prepared standard solution “blanks”, even those prepared under “clean-lab” conditions
Summary
In recent years Environmental and Earth Science research programmes have benefitted greatly from the application of Inductively Coupled Plasma Mass Spectrometric (ICP-MS) trace element analyses (Potts, 1987; Jenner et al, 1990; Linge & Jarvis, 1997; Makishima & Nakamura, 2006; Chauvel et al, 2010). In analyses carried out in 2017 we attempted to avoid using an internal standard but during data-reduction we found that the ICP-MS data for solutions having dilution factors (DF) of 500 (TDS < 2000 μg·g−1) generally gave lower concentrations than those for the most reliable elements determined by XRF (e.g., Ni, Ba, Ce) and ID (e.g., Nd, Sm) for the same Marangudzi rocks while the BCR-1, BHVO-1, AGV-1, and G-2 samples normalised to the recommended concentrations for most elements gave slightly lower ratios (e.g., REE ~0.90 ± 0.05) than expected. We aim is to establish as straightforward a protocol as possible for digesting, analysing and standardising trace element concentrations for mixed batches of rocks ranging from basaltic to alkali-, and trace-element-rich, under- and over-saturated igneous rocks without time-consuming chemical separations and multi-internal-standard corrections to deal with matrix effects. Rock powders were prepared for analyses in a general-purpose chemical analytical laboratory but the initial solutions (DF500) were diluted where necessary and analysed by ICP-MS in a class 1000 cleanroom
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