AfzAli et Al.: JournAl of AoAC internAtionAl Vol. 96, no. 1, 2013 161 Ultrasound-Assisted Ion-Pair Dispersive Liquid–Liquid Microextraction of Trace Amounts of Lead in Water Samples Prior to Graphite Furnace Atomic Absorption Spectrometry Determination Daryoush afzali International Center for Science, High Technology & Environmental Sciences, Research Institute of Environmental Sciences, Environment Department, Kerman, Iran ali reza MohaDesi Payame Noor University, Department of Chemistry, 19395-4697, Tehran, Iran MasouMeh falahnejaD and Behnoosh BahaDori International Center for Science, High Technology & Environmental Sciences, Research Institute of Environmental Sciences, Environment Department, Kerman, Iran Payame Noor University, Department of Chemistry, 19395-4697, Tehran, Iran Received April 20, 2011. Accepted by AK June 24, 2011. Corresponding author’s e-mail: daryoush_afzali@yahoo.com DOI: 10.5740/jaoacint.11-174 RESIDUES AND TRACE ELEMENTS A new ion-pair dispersive liquid–liquid microextraction method is described for separation and preconcentration of trace amounts of lead in different water samples. Graphite furnace atomic absorption spectrometry was used for determination of lead. The ion association complex between lead and iodide ions that forms is PbI 4 –2 -tetradecyl- dimethylbenzylammonium, which is extracted into fine droplets of chlorobenzene. In order to reach the optimized experimental conditions, the influence of different parameters, such as concentration of KI, nature and volume of extraction solvents, pH effect, extraction time, and the period and speed of sonication and centrifugation, were optimized. The LOD was 0.08 ng/mL and the linear dynamic range was 0.20–8.0 ng/mL in initial solution with a correlation coefficient of 0.9985. Under the optimum conditions, the enrichment factor was 555.5. The proposed method was successfully applied for separation and determination of lead in sea, rain, river, and drinking water samples. I n recent years, human activities have resulted in pollution of the environment by large amounts of toxic elements. Exposure to these toxic elements imposes risks not only to human health, but also to plants, animals, and microorganisms (1). Determination of trace heavy metals ion in various materials from industrial samples to environmental samples has been performed continuously (2). Lead is one of the most toxic elements, has an accumulative effect, and is an environmental priority pollutant (3). The harmful effects on human health caused by lead contamination are well known, among them are the reduction of the enzymatic activity and kidney function, and neuromuscular difficulties (4). The environmental and health problems arise fundamentally from the use of gasoline antiknock products and paint pigments (5). As a consequence, the World Health Organization has reported the maximum allowable limit of 10.0 ng/L for lead in drinking water (6). It is therefore important to monitor the lead level in environmental samples. Currently, the most common analytical methods for lead trace determination are flame atomic absorption spectrometry (FAAS; 7, 8), electrothermal or graphite furnace AAS (GFAAS; 9–11), and inductively coupled plasma atomic emission spectrometry (12). Separation and preconcentration steps are usually required before determination of trace amounts of elements. This is due to their low concentrations and matrix effects in the environmental samples (13). Several procedures, such as liquid–liquid extraction (14–17), co-precipitation (18), and SPE (19–21), have been developed for separation and preconcentration of lead from environmental matrixes. These methods have disadvantages such as significant chemical additives, solvent losses, complex equipment, large secondary wastes, unsatisfactory enrichment factors, and high time consumption. These problems could be overcome by the development of modular, simple, and compact processes that provide adequate separation and preconcentration. The solvent microextraction technique effectively overcomes these difficulties by reducing the amount of organic solvent and using single step extraction and preconcentration. Dispersive liquid–liquid microextraction (DLLME) is based on the formation of tiny droplets of the extractant in the sample solution using a water-immiscible organic solvent (extractant) dissolved in a water-miscible organic dispersive solvent (22–24). Its main drawback is the necessity of using a third component (disperser solvent), which usually decreases the partition coefficient of analytes into the extraction solvent (25). The advantages of the DLLME method are rapidity, low cost, and high enrichment factors. The technique is faster and simpler than conventional methods. It is also sensitive and effective for reducing the matrix effects. One manipulation step reduces or removes the contamination and loss of analytes. This procedure is time-consuming because it is operated in a batch mode. In addition, this procedure produces large amounts of potentially toxic organic solvent waste. These drawbacks could be overcome by the implementation of supplementary techniques