Pre-concentration of thorium and neodymium isotopes using Nobias chelating resin: Method development and application to chromatographic separation

• Published in: Talanta (Oxford) 2019-09, Vol.202, p.600-609
• Main Authors: Pérez-Tribouillier, Habacuc, Noble, Taryn L., Townsend, Ashley T., Bowie, Andrew R., Chase, Zanna
• Format: Article
• Language: English
• Subjects: Chromatographic separation; GEOTRACES; Neodymium; Nobias® resin; Seawater; Thorium
• ISSN: 0039-9140; 1873-3573
• DOI: 10.1016/j.talanta.2019.03.086

The isotopes of thorium (Th) and neodymium (Nd) are used as tracers in oceanography, and are key parameters in the international GEOTRACES program. The very low concentrations of Th and Nd as well as the reactive nature of Th isotopes makes the analysis of seawater samples a complex process. Analysis requires time-consuming pre-concentration from over 5 L of seawater. We describe a method to simultaneously pre-concentrate dissolved Th and Nd from acidified seawater samples using the Nobias® PA1L chelating resin. Prior to pre-concentration, hydrofluoric acid is added to the sample to stabilise Th, ammonium acetate buffer added (0.05 M), pH adjusted to 4.75, and then finally the prepared sample is pumped through the Nobias resin at a rate of 15 ml min−1. Up to 6 samples can be processed simultaneously. Following elution in 3 M HNO3, both elements are chromatographically separated and determined using Inductively Coupled Plasma Mass Spectrometry. Oxidation of the sample between all column separation steps, including after the initial Nobias resin, is important for obtaining maximum elemental recoveries. The method has >90% recovery with blank levels typically