Concomitant measurement of 143Nd/144Nd and 147Sm/144Nd ratios without isotope dilution in geological samples: An assessment of MC-ICP-MS capabilities

A new analytical procedure is described for the simultaneous determination of 143Nd/144Nd and 147Sm/144Nd ratios in geological samples that alleviates the use of isotope dilution with isotopically enriched tracers, and the need for chemical separation of Sm and Nd from each other and other LREE. The method first involves the chemical separation of a LREE fraction from matrix elements by using a procedure combining cation-exchange chromatography and extraction chromatography columns. Then, isotope ratio measurements are made by using a MC-ICP-MS instrument, with sample introduction through a commercially available 2-step desolvation system. This device allows to greatly reduce the production of the Nd oxide species, thereby eliminating the major cause of mutual fractionation of Sm and Nd in the plasma ion source. The specific semi-empirical procedures necessary for correcting for instrumental mass bias effects and isobaric interferences are described. The potential of this approach for routine analysis of geological samples is evaluated through replicate measurements of a set of geological reference materials, well characterized by using the conventional ID-TIMS reference method. Although slightly less powerful than state-of-the-art ID-TIMS methods in terms of ultimate precision and accuracy achievable, the MC-ICP-MS approach is able to provide reproducible 143Nd/144Nd and 147Sm/144Nd results with precision and accuracy adequate for most routine geochemical work, while offering very significant advantages in terms of sample preparation effort and overall analytical throughput.

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► Concomitant measurement of 143Nd/144Nd and 147Sm/144Nd ratios without isotope dilution.
► Correction procedures for instrumental mass bias effects and isobaric interferences.
► Validation on CRMs.
► Advantages in terms of sample preparation effort and overall analytical throughput over ID-TIMS.
► Assessment of MC-ICP-MS capabilities.