Development of a dispersive liquid–liquid microextraction combined with flame atomic absorption spectrometry using a microinjection system for the enrichment, separation, and determination of nickel in water samples Zeid A. Al Othman a , Erkan Yilmaz b , Mohamed Habila a , Mustafa Soylak b, * a Chemistry Department, College of Science, King Saud University, Riyadh 11451, Kingdom of Saudi Arabia b Fen Fakultesi, Department of Chemistry, Erciyes University, Kayseri 38039, Turkey Tel./Fax: +903524374933; email: soylak@erciyes.edu.tr Received 19 June 2012; Accepted 30 January 2013 ABSTRACT A simple, rapid dispersive liquid–liquid microextraction procedure was combined with flame atomic absorption spectrometry and has been established for the determination of trace amounts of nickel. A mixture of carbon tetrachloride, 2-(5-bromo-2-pyridylazo)-5-diethyl- amino-phenol (5-Br-PADAP), and acetonitrile was swiftly injected with a syringe into a sample containing nickel(II) resulting in the formation of a cloudy solution. The cloudy solution was centrifuged and fine droplets settled at the bottom of the test tube. After centrifuging, the settled organic phase was dissolved to a total volume of 250 lL in concentrated nitric acid, from which 25 lL was introduced into the flame atomic absorption spectrometer using the microin- jection system. The effect of parameters such as pH, the amount of 5-Br-PADAP, the volume and types of the extraction, and dispersion solvents have been examined. The limit of detection, the preconcentration factor, and enhancement factors were 0.13 lgL À1 , 200, and 99, respectively. The calibration graph was linear in the rage of 5–186 lgL À1 . The developed method was validated by analyzing certified reference materials (TMDA-25.3, TMDA-51.3). The microextraction method was satisfactorily used for the determination of nickel(II) in various environmental waters. Keywords: Preconcentration; Microextraction; Nickel; Water; Atomic absorption spectrometry 1. Introduction Transition metal such as nickel can be essential or toxic to human beings depending on its concentration. Nickel is apparently essential for proper functioning of the liver; however, some nickel compounds are carcinogens [1–4]. Therefore, the accurate and precise determination of nickel in environmental samples is very important. Many instrumental techniques, such as flame and electrothermal atomic absorption spec- trometry, atomic fluorescence spectrometry, and inductively coupled plasma mass spectrometry, are available for determining trace quantities of nickel and other metal ions [5,6]. However, enrichment and separation are generally required prior to the determi- nation step because of low levels of metal ions and interferences of the sample matrix [7–9]. Solvent *Corresponding author. 1944-3994/1944-3986 Ó 2013 Balaban Desalination Publications. All rights reserved. Desalination and Water Treatment www.deswater.com doi: 10.1080/19443994.2013.792447 51 (2013) 6770–6776 October Downloaded by [Universiteit Twente] at 02:38 03 November 2013