We describe here the amino-functionalization of multiwall carbon nanotubes (MWCNTs) and also its application as an adsorbent of solid phase extraction (SPE). The amino-functionalized MWCNTs have a good capacity to retain Hg2+, but the raw and purified MWCNTs are found not to adsorb Hg2+ ions. The amino-functionalized MWCNTs are prepared with amino-functionalization of purified MWCNTs by ethylenediamine. The physicochemical properties of purified and amino-functionalized MWCNTs are characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and the Boehm titration. The amino-functionalized MWCNTs are selected as novel sorbents for the solid phase extraction of Hg2+. The amino-functionalized MWCNT-SPE method is used for the determination of Hg2+ from complex matrix including fish and real water samples. Effective parameters on Hg2+ retention such as pH, flowrate, nature of the eluent, the ionic strength, selectivity coefficient, and retention capacity are investigated. The enrichment factor and maximum capacity of the sorbent are 100？mL and 11.58？mg/g, respectively. The linear range, limit of detection, and relative standard deviation of the proposed method are 0.003 to 0.3？μg/L, ？μg/L, and 2.23%, respectively. Selectivity experiments show that the adsorbents have a stronger specific retention for Hg2+ than Fe3+, Cu2+, Pb2+, Ni2+, Mn2+, Ca2+, and Mg2+. 1. Introduction Mercury presents as different species in different environmental media including atmosphere, soil, sediment, natural waters, waste water, and water body. Mercury pollution in water has a negative impact on the aquatic organism and human. Speciation of mercury in water is very important for evaluation of mercury pollution [1, 2]. Mercury is also a kind of environmental hormone, which can destroy the functions of natural metabolism and incretion, procreate for organism, and lead to maladjustment in hormone secretion of organism. At the same time, mercury is widely dispersed in natural world because of its extensive applications [3]. It is well known that mercury is one of the most toxic heavy metals. In contaminated environment, different forms of mercury can be accumulated in animals and plants and also enter into human body by food cycle, resulting in the damage of central nerve. Because of mercury accumulative and persistent character in the environment and living organisms, lethal concentrations of mercury salts range from less than 0.1？ng/mL to more than 200.0？ng/mL for marine species and freshwater organisms [4]. Mercury is a nonessential toxic element and is
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