Routine high-precision Nd isotope analyses: an optimized chromatographic purification scheme

Abstract

High-precision Nd isotope measurements provide key constraints on the evolution of the silicate Earth and planetary bodies. As advances in mass-spectrometry and measurement techniques have brought the precision of ¹⁴²Nd/¹⁴⁴Nd measurements down to ±2 ppm (parts-per-million), systematic biases stemming from insufficient sample purification (matrix effects and/or isobaric interferences) or non-quantitative yields are becoming increasingly problematic. One of the most widespread approaches for Nd purification uses cation-exchange column chromatography with α-HIBA (2-methylactic acid) reagent. Despite its popularity, limitations pertaining to the level of purification and yield of the α-HIBA method exist. Here we present an optimized α-HIBA purification protocol that addresses these limitations and achieves the level of purity required for routine high-precision Nd isotope analyses. This protocol builds on existing methodologies and a comprehensive series of tests that we performed, and efficiently minimizes procedural blanks, the number of column passes, and thus the sample processing time, while maximizing recovery yields. We anticipate that this optimized protocol will benefit both established and new users of the α-HIBA column chromatography method.