Determination of 232Th in seawater by ICP-MS after preconcentration and separation using a chelating resin

This article describes an analytical method for the separation, preconcentration and determination of 232Th in seawater samples at sub-ng/L levels using a NOBIAS CHELATE PA1 resin and a sector field (SF) inductively coupled plasma mass spectrometer (ICP-MS). The resin showed excellent adsorption of 232Th at a low pH of 2.4 ± 0.4 in a relatively small volume (200 mL) of seawater. 232Th adsorbed on the resin was easily eluted using 5 mL of 0.8 M HNO3. An enrichment factor of 40 was achieved for 232Th analysis. Ethylenediamine-tetraacetic acid disodium salt dehydrate (EDTA) was used to investigate the effect of 232Th-binding organic ligand on the retention of 232Th on the chelating resin. Results obtained using acidified samples (pH of 2.4 ± 0.4) showed EDTA had no significant effect on 232Th recovery, indicating that at this low pH, 232Th was dissociated from the 232Th-binding organic ligand and quantitatively retained on the NOBIAS CHELATE PA1 resin. The developed analytical method was characterized by a separation and preconcentration taking approximately 4 h and a low detection limit of 0.0038 ng/L for 232Th, and was successfully applied to the determination of 232Th in seawater samples collected from coastal areas, Japan.