Analytica Chimica Acta 804 (2013) 120–125 Contents lists available at ScienceDirect Analytica Chimica Acta jou rn al h om epage: www.elsevier.com/locate/aca Rapid collection of iron hydroxide for determination of Th isotopes in seawater Ayako Okubo a,∗ , Hajime Obata b,1 , Masaaki Magara a,2 , Takaumi Kimura a,3 , Hiroshi Ogawa b,4 a Japan Atomic Energy Agency, Research Group for Analytical Chemistry, Japan b Atmosphere Ocean Research Institute, The University of Tokyo, Japan h i g h l i g h t s • DIAION CR-20 chelating resin has successfully collected iron-hydroxide with Th isotopes. • Ferric ions in the iron hydroxide were bonded to functional groups of the chelating resin. • The time of preconcentration step was markedly reduced from a few days to 3–4 h. g r a p h i c a l a b s t r a c t a r t i c l e i n f o Article history: Received 24 June 2013 Received in revised form 30 September 2013 Accepted 3 October 2013 Available online 12 October 2013 Keywords: Thorium isotopes Seawater Iron hydroxides co-precipitation Chelating resin a b s t r a c t This work introduces a novel method of recovery of iron hydroxide using a DIAION CR-20 chelating resin column to determine Th isotopes in seawater with a sector field (SF) inductively coupled plasma mass spectrometer (ICP-MS). Thorium isotopes in seawater were co-precipitated with iron hydroxide, and this precipitate was sent to chelating resin column. Ferric ions in the iron hydroxide were bonded to functional groups of the chelating resin directly, resulting in a pH increase of the effluent by release of hydroxide ion from the iron hydroxide. The co-precipitated thorium isotopes were quantitatively collected within the column, which indicated that thorium was retained on the iron hydroxide remaining on the chelating column. The chelating column quantitatively collected 232 Th with iron hydroxide in seawater at flow rates of 20–25 mL min -1 . Based on this flow rate, a 5 L sample was processed within 3–4 h. The >20 h aging of iron hydroxide tends to reduce the recovery of 232 Th. The rapid collection method was successfully applied to the determination of 230 Th and 232 Th in open-ocean seawater samples. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Thorium is one of the most important tracers to understand particle dynamics in the ocean. In an international research project, GEOTRACES, Th isotopes in seawater are listed up as ∗ Corresponding author. Tel.: +81 29 284 3667; fax: +81 29 284 6950. E-mail addresses: okubo.ayako@jaea.go.jp (A. Okubo), obata@aori.u-tokyo.ac.jp (H. Obata), magara.masaaki@jaea.go.jp (M. Magara), kimura.takaumi@jaea.go.jp (T. Kimura), hogawa@aori.u-tokyo.ac.jp (H. Ogawa). 1 Tel.: +81 4 7136 6082; fax: +81 4 7136 6081. 2 Tel.: +81 29 284 5544; fax: +81 29 284 6950. 3 Tel.: +81 29 284 3664; fax: +81 29 284 6950. 4 Tel.: +81 4 7136 6091; fax: +81 4 7136 6081. a key parameter to better understanding of marine biogeo- chemical cycles [1]. In this project, to determine Th isotopes in seawater ( 230 Th: 0.42–53 fg kg -1 , 232 Th: 24–229 pg kg -1 ) [2,3], an iron hydroxides co-precipitation method is applied for 5–10 L of seawater sample [4]. Iron hydroxides co-precipitation method [5,6] has been widely used for preconcentration of radioisotopes in seawater samples, such as 230 Th, 231 Pa, and 10 Be and Pu isotopes, whose concentrations in seawater are extremely as low as a few fg kg -1 . The iron hydroxides co-precipitation method is conventional but considerably time- consuming, requiring 3–6 days to collect Th isotopes from seawater [7,8]. Recently a solid-phase extraction method with a chelating resin containing ethylenediamine triacetic acid functional groups was 0003-2670/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.aca.2013.10.004