Evaluation of two methods allowing the full preparation in a single day of silicate rocks in view of radiogenic isotope (Nd, Sr, and Pb) analyses

Abstract

In this paper, two approaches are described aiming to circumvent the bottle-neck associated with sample decomposition of silicate samples and subsequent isolation of three elements (Nd, Sr, and Pb) of major interest for their radiogenic isotope compositions. These new methods alleviate the need for any evaporation and repeated dissolution steps and make it possible to achieve in a single day the complete preparation of a batch of 10 samples. Specifically, samples are decomposed either by alkaline fusion with a LiBO₂ flux followed by quenching in nitric acid, or by quick dissolution in an HF–HNO₃ mixture immediately followed by reaction with an aqueous solution of boric acid to neutralize excess HF and dissolve sparingly soluble fluorides. In both cases, the resulting sample solutions are directly loaded onto small chromatographic columns filled with RE and Sr resins, respectively, used in tandem, in order to achieve the concomitant separation of the LREE, Sr, and Pb from matrix elements. While Sr and Pb fractions suitable for isotopic analyses are directly stripped from the Sr resin, an additional column of DGA resin is used, in tandem with the RE resin column, to obtain a Nd fraction isolated from the other LREE. The potential of these most straightforward approaches is demonstrated by repeated analyses of eleven geological reference materials (RMs) spanning a wide range of major element concentrations.