| Mercury and its derivatives are the most toxic global-spreaded pollutants, widely existing in atmosphere, water, soil, plants, animals and other biotas. The high toxicity of mercury has gained extensive attention due to its remarkable accumulation feature. The toxicity of mercury varies according to its chemical forms. Organic mercury, especially methylmercury, is more toxic than inorganic mercury. Therefore, it is highly essential to develop new analytical methods with high sensitivity and selectivity for the determination of mercury and its speciation in various sample matrixes.Polyhedral oligomeric silsesquioxane (POSS), consist of an inorganic cubic Si8O12 core surrounded by eight organic groups, is a kind of nano cage-material with organic-inorganic hybrid structure. It can be functionalized with a variety of organic groups. POSS is usually porous and 1.5 nm in diameter, with high surface area and favorable biocompatibility. This feature offers great potential in solid phase extraction. In the present work, mercaptopropyl polyhedral oligomeric silsesquioxane (POSS-SH) is prepared via hydrolytic condensation of 3-mercaptopropyl trimethoxysiliane. The as-prepared POSS-SH shows strong affinity to Hg2+ and CH3Hg+ due to the abundant thiol group on the surface. It has been demonstrated that under optimal conditions, adsorption efficiency of 93% and 94% is achieved for Hg2+ and CH3Hg+ by using 8.0 mg POSS-SH as sorbent, respectively. The adsorption of Hg2+ and CH3Hg+ fits the Langmuir adsorption model, corresponding to a theoretical adsorption capacity of 12.90 mg g-1 and 46.73 mg g-1. The retained Hg2+ and CH3Hg+ can be readily recovered by using thiourea (2%, m/v) in 2 mol L-1 HCl as the stripping reagent. By combining solid phase extraction separation and preconcentration with atomic fluorescence spectrometry, it is feasible to determine the content of mercury and its speciation. Hg2+ and total mercury can be quantified respectively by adopting different atomization modes of atomic fluorescence spectrometry after preconcentration with POSS-SH as the sorbent material. Hg2+ is quantified by non-flame atomization mode with a NaBH4 concentration of 0.0001%(m/v), while total amount of mercury is determined by adopting flame atomization mode with a much higher NaBH4 concentration of 1%(m/v). The amount of CH3Hg+is thus derived by difference. With a sample volume of 4.0 mL and an eluent volume of 400 ?L, enrichment factors of 8.9 for Hg2+ and 9.3 for CH3Hg+ are achieved. Hg2+ and CH3Hg+ could be accurately quantified in the range of 0.005?2.0?g L-1 and 0.01?2.0?g L-1, along with detection limits of 2 ng L-1 (3a, n=11) Hg2+ and 4 ng L-1 (3a, n=9) CH3Hg+, respectively. The relative standard deviation for Hg2+(0.1?g L-1, n=11) and CH3Hg+(0.1?g L-1, n=9) are 3.5% and 3.1%. This method is validated by the analysis of mercury in certified water reference material (GBW 08603). Speciation of Hg2+ and CH3Hg+ in nature water and the extract of cosmetic are performed, and satisfactory spiking recoveries are obtained. |
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