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 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) 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