Available online at www.sciencedirect.com Journal of Hazardous Materials 150 (2008) 533–540 Cloud point extraction for the determination of copper, nickel and cobalt ions in environmental samples by flame atomic absorption spectrometry M. Ghaedi a,∗ , A. Shokrollahi a , F. Ahmadi a , H.R. Rajabi a , M. Soylak b a Chemistry Department, University of Yasouj, Yasouj 75914-353, Iran b Chemistry Department, University of Erciyes, 38039 Kayseri, Turkey Received 30 October 2006; received in revised form 1 May 2007; accepted 1 May 2007 Available online 16 May 2007 Abstract A cloud point extraction procedure was presented for the preconcentration of copper, nickel and cobalt ions in various samples. After complexation with methyl-2-pyridylketone oxime (MPKO) in basic medium, analyte ions are quantitatively extracted to the phase rich in Triton X-114 following centrifugation. 1.0 mol L -1 HNO 3 nitric acid in methanol was added to the surfactant-rich phase prior to its analysis by flame atomic absorption spectrometry (FAAS). The adopted concentrations for MPKO, Triton X-114 and HNO 3 , bath temperature, centrifuge rate and time were optimized. Detection limits (3 SDb/m) of 1.6, 2.1 and 1.9 ng mL -1 for Cu 2+ , Co 2+ and Ni 2+ along with preconcentration factors of 30 and for these ions and enrichment factor of 65, 58 and 67 for Cu 2+ , Ni 2+ and Co 2+ , respectively. The high efficiency of cloud point extraction to carry out the determination of analytes in complex matrices was demonstrated. The proposed procedure was applied to the analysis of biological, natural and wastewater, soil and blood samples. © 2007 Elsevier B.V. All rights reserved. Keywords: Methyl-2-pyridylketone oxime (MPKO); Cloud point extraction; Triton X-114; Flame atomic absorption spectrometry 1. Introduction The importance of the determination of trace metal concen- tration in natural water samples is increasing in contamination monitoring studies. The determination of trace of these ions in biological samples is particularly difficult because of the complex matrix and the usually low concentration of these ele- ments in such samples, which requires sensitive instrumental techniques and frequently a preconcentration step [1,2]. Solvent extraction is widely used in hydrometallurgy [3] and especially for the partitioning process for spent nuclear fuel reprocessing [4]. However, this technique exhibits important drawbacks due to the extensive use of volatile organic diluents which are often toxic and flammable. The pressure to decrease organic solvent use in industries has encouraged the requirement for solvent-free procedures for which supramolecular assem- blies are excellent candidates. Supramolecular assemblies result from the spontaneous association of a large number of com- ∗ Corresponding author. Tel.: +98 741 2223048; fax: +98 741 2223048. E-mail address: m ghaedi@mail.yu.ac.ir (M. Ghaedi). ponents into a specific phase (i.e., micelles, vesicles) and new separation methods based on innovative concepts are currently being developed [5–8] as an interesting alternative to traditional liquid–liquid solvent extraction. The solubility of non-ionic surfactants in aqueous solution is depressed above a well-defined temperature known as cloud point temperature (CPT). By setting the solution at a tempera- ture above CPT, the solution separates into a concentrated phase containing most of the surfactant, the coacervate phase and a dilute aqueous phase. Cloud point extraction (CPE) arises from the partitioning of a solute between the two water-based phases depending on its affinity to the surfactant. Such an extraction offers a convenient alternative to more conventional extraction systems. Aqueous solutions of non-ionic and zwitterionic sur- factants possess the ability to decrease their solubility quickly and become turbid when heated above a temperature referred to as the cloud-point [9,10]. For higher temperatures, two distinct phases are formed, one consisting almost totally of the surfactant and the other contain- ing a small portion equal to the critical micellar concentration (CMC) [11,12]. The mechanism by which this separation occurs is attributed to the rapid increase in the aggregation number of the 0304-3894/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jhazmat.2007.05.029