Talanta 64 (2004) 13–17 Determination of nickel in natural waters by FAAS after sorption on octadecyl silica membrane disks modified with a recently synthesized Schiff’s base Afshin Rajabi Khorrami a , Hossein Naeimi b , Ali Reza Fakhari a,∗ a Department of Chemistry, Shahid Beheshti University, Tehran, Iran b Department of Chemistry, Kashan University, Kashan, Iran Received 12 August 2003; received in revised form 19 October 2003; accepted 21 October 2003 Abstract A simple, highly sensitive, accurate and selective method for the determination of trace amounts of Ni 2+ ions in water samples is proposed. The method is based on the separation and preconcentration of Ni 2+ on an octadecyl-bonded silica (ODBS) membrane disk modified by a recently synthesized Schiff’s base N,N ′ -bis (3-methylsalicylidene) ortho phenylene diamine (MSOPD) at pH 7. The synthesis of this extractant ligand is also described. The retained nickel on the membrane was eluted with 2 × 5 ml 0.5 M HNO 3 and measured by flame atomic absorption spectrometry (FAAS) at 232.0nm. The extraction efficiency and the influence of the type and least amount of eluent for the stripping of Ni 2+ from the disks, pH, flow rates of sample solution and eluent, amount of MSOPD, effect of other ions, and breakthrough volume were evaluated. The maximum capacity of the membrane disks modified by 3 mg of MSOPD was found to be 146 ± 4 g Ni 2+ . The 3σ limit of detection of the method was 30 ng per 1000 ml and also an enrichment factor of 250 was obtained. The proposed method has been applied to the determination of nickel in several water samples with satisfactory results. © 2004 Elsevier B.V. All rights reserved. Keywords: Nickel determination; SPE; Preconcentration; Separation; N,N ′ -bis (3-methylsalicylidene) ortho phenylene diamine; FAAS 1. Introduction The importance of the determination of heavy metal ions, such as nickel, in environmental samples can hardly be overemphasized because they have undoubtedly a serious potential hazard to the human organism. The main sources of nickel in aquatic systems are from dissolution of rocks and soils, biological cycles, atmospheric fallout, and espe- cially industrial processes and water disposal [1]. Nickel is the metal component of the enzyme urease and as such con- sidered to be essential to plants. Evidence has also been presented nickel being essential to some domestic animals. Essentiality of nickel to man does not yet seem to have been demonstrated. More attention has been focussed on the toxicity of nickel in low concentrations, such as the fact that nickel can cause allergic reactions and that certain ∗ Corresponding author. E-mail address: a-zavareh@cc.sbu.ac.ir (A.R. Fakhari). nickel compounds are carcinogenic [2]. The maximum rec- ommended concentration of nickel ion in drinking water for livestock is 2.5 mg l -1 [3]. For drinking water for human consumption the upper limits are even less. The develop- ment of reliable, yet affordable, analytical approaches for the determination of Ni 2+ in low concentration levels seems worthwhile. Nickel determination in water samples could be carried out directly by electrothermal atomic absorption spec- trometry (ETAAS) or by inductively-coupled plasma mass spectrometry (ICP-MS), which have usually enough limit of detection [4,5]. Flame atomic absorption spectrometry (FAAS), which is an available technique in most labora- tories and is normally less subjected to interferences than ETAAS or ICP-MS, requires the use of a preconcentration step in order to reach an appropriate level of sensitivity. Preconcentration of the nickel ion prior to analysis can not only concentrate the analyte but also simplify the matrix of the sample. Solid-phase extraction (SPE) has received much attention in recent years for the analysis of trace con- 0039-9140/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.talanta.2003.10.057