ORIGINAL PAPER Hiroaki Matsumiya Æ Nobuhiko Iki Æ Sotaro Miyano Masataka Hiraide Preconcentration of copper, cadmium, and lead with a thiacalix[4]arenetetrasulfonate-loaded Sephadex A-25 anion-exchanger for graphite-furnace atomic-absorption spectrometry Received: 19 January 2004 / Revised: 8 April 2004 / Accepted: 20 April 2004 / Published online: 4 June 2004 Ó Springer-Verlag 2004 Abstract A rapid column-adsorption method has been developed for concentrating traces of copper, cadmium, and lead in water prior to their determinations by graphite-furnace atomic-absorption spectrometry. The adsorbent used was prepared by loading a strongly basic anion-exchanger QAE-Sephadex A-25 (50 mg) with thiacalix[4]arenetetrasulfonate (20 lmol). Two-hun- dredfold preconcentration of the analyte elements was achieved by passing 100 mL of sample solution (pH 8.0) through a column packed with the adsorbent (6 mm i.d.·7 mm high) at a flow rate of 10 mL min À1 and by the subsequent elution with 500 lL of aqueous nitric acid solution (1 mol L À1 ). The practical applicability of the proposed method was evaluated by analyzing certi- fied reference seawater samples. Keywords Preconcentration Æ Chelating adsorbent Æ Calixarene Æ Heavy metals Æ Atomic-absorption spectrometry Æ Seawater Introduction Adsorption of metals from water on to a chelating adsorbent is a powerful means of selective concentration of traces of the metals with a high concentration factor [1]. By passing a water sample through a column packed with an appropriate adsorbent, the desired metals are effectively collected on the column. The collected metals are subsequently desorbed with a small volume of eluent for determination by instrumental analytical methods. For this purpose, a wide variety of chelating adsorbents have been prepared by loading or chemically modifying solid supports with selective chelating agents [2–4]. As is well-known, chelating agents with auxiliary ionic function groups can be retained on common solid ion-exchangers by electrostatic interaction, thus pro- viding a facile way of preparing selective chelating adsorbents [5–9]. In a previous study, a strongly basic anion-exchanger Amberlite IRA-900 (macroreticular cross-linked polystyrene resin with trimethylammonium groups) was loaded with an anionic chelating agent thiacalix[4]arenetetrasulfonate (TCAS, Fig. 1) and examined for its metal-adsorption characteristics [10]. In contrast with its poor adsorption of alkaline and alka- line earth metals, the TCAS-loaded IRA-900 resin retained heavy metals strongly, owing to the selective coordination of the sulfide groups in TCAS to the metal center with the cooperative chelation of the adjacent phenoxides. This selective adsorption behavior was favorable for concentrating trace heavy metals in water samples, but the analytical use of the TCAS-loaded IRA-900 resin seemed to be rather impractical because quantitative adsorption required slow passage of the sample through the column, typically at a flow rate of 0.1 mL min À1 . The use of a hydrophilic solid support often endows the resulting chelating adsorbent with fast adsorption kinetics. For instance, several literature reports describe fast metal-adsorption behavior of some polysaccharide- based chelating adsorbents [11–13]. In the present study we therefore used a dextran-based anion-exchanger QAE-Sephadex A-25 as the solid support to improve the adsorption kinetics. The column adsorption system with the TCAS-loaded Sephadex A-25 enabled rapid pre- concentration of copper, cadmium, and lead at a flow rate of 10 mL min À1 . The proposed method gave a high concentration factor of 200 and was successfully applied to the analysis of seawater samples by graphite-furnace atomic-absorption spectrometry (GFAAS). H. Matsumiya (&) Æ M. Hiraide Department of Molecular Design and Engineering, Graduate School of Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603, Japan E-mail: h-matsu@numse.nagoya-u.ac.jp Tel.: +81-52-7893591 Fax: +81-52-7893241 N. Iki Æ S. Miyano Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Aoba-ku, Sendai 980-8579, Japan Anal Bioanal Chem (2004) 379: 867–871 DOI 10.1007/s00216-004-2655-5