Solvent Extraction-Mediated Fractionation of Copper in Waters at Natural pH Conditions Cristina Vergel, Carolina Mendiguchı ´a, and Carlos Moreno Faculty of Marine and Environmental Sciences, Department of Analytical Chemistry, University of Cadiz, Puerto Real, Spain A new solvent extraction system using a hydrazone derivative such as 1,2-cyclohexanedione bis-benzoylhydrazone (1,2-CHBBH) has been studied to separate and quantify the different fractions of copper present in natural waters. The influence of different variables on the extraction has been studied, such as the type of organic solvent, the reagent concentrations in the extraction and back- extraction solutions, the sample pH, and the extraction time. Under selected conditions, the influence of both organic and inorganic ligands present in natural waters on the efficiency of the extraction process has been also investigated. Thus, the effect of the major anion species present in this kind of sample (Cl  , HCO  3 , SO 2 4 , Br  ) as well as the effect of humic substances have been analyzed. Differences in the extraction efficiency were observed when organic ligands were presented in the samples. These differences allow the selective separation and quantification of the non-labile copper fraction in natural waters. Keywords 1,2-CHBBH; copper; labile; natural waters; speciation INTRODUCTION It is generally agreed that the bioavailability of trace metals in natural waters, and therefore their toxicity, is related to their different chemical forms (1). In the case of copper, several studies have demonstrated that humic substances (HS) are protective against copper toxicity in several organisms and such an effect is caused by the reduction in labile copper due to Cu-HS complexation (2–5). In order to determine the potential toxicity of copper in natural waters, the use of a technique allowing a simple and selective separation of the different species present in natural waters is essential. Solvent extraction has been widely used for the separ- ation and preconcentration of trace amounts of metal ions, including copper, with different aims. On the one hand, the extraction of copper from waste solutions has been developed to both reduce the environmental impact of wastewaters and recover valuable metals. In this sense, several applications can be found to extract copper from acidic wastes of the printed circuit board industry (6), smelt- ing residues of pyro-metallurgical processes (7), or sulphuric liquors generated by zinc production (8). On the other hand, some analytical applications have been described to extract and preconcentrate copper from natural waters before its determination by atomic absorption spectrometry or high performance liquid chromatography (9–12). However, most of the solvent extraction applications have been developed to extract total copper concentration by means of several commercial reagents. Among them, chelating aldoximes or ketoximes (named as LIX) are undoubtedly the most extensively used (13–19). In addition, organophosphorus compounds such as DEHPA and Cyanex, as well as the quaternary ammonium salt Aliquat 336, have been also used in different applications (13,15,20). Most of these commercial reagents need an acidic medium for metal extraction, and then the develop- ment of new synthesized compounds offers a good alterna- tive for extractions from neutral solutions, such as natural waters, and improving the selectivity and sensitivity of the extraction methods, as well as its applicability. In this sense, some examples can be found using phosphinic acid derivatives (21), hydrazone oximes (22), and some Schiff base extractants (23,24) among others. Aroylhydrazone derivatives have demonstrated their ability to form metal complexes at neutral or slightly basic pH values, allowing their application as a selective reagent in chemical specia- tion of natural waters (25–27). What is more, its ability to quantify different fractions of nickel in natural waters under the presence of humic substances has been probed by previous studies (28). In the present work, we have studied a solvent extrac- tion system to perform the selective separation of the different fractions of copper present in natural waters using the hydrazone derivative 1,2-cyclohexanedione bis-benzoylhydrazone (1,2-CHBBH), which has been previously used for nickel fractionation in waters (28). First, the influence of some chemical variables was studied Received 21 October 2011; accepted 27 February 2012. Address correspondence to Carolina Mendiguchı ´a, Faculty of Marine and Environmental Sciences, Department of Analytical Chemistry, University of Cadiz, 11510 Puerto Real, Spain. Fax: Fax: þ34 956016460. E-mail: carolina.mendiguchia@uca.es Separation Science and Technology, 47: 2430–2435, 2012 Copyright # Taylor & Francis Group, LLC ISSN: 0149-6395 print=1520-5754 online DOI: 10.1080/01496395.2012.671433 2430 Downloaded by [Universitetsbiblioteket i Oslo] at 05:50 27 November 2012