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The potential of graphene as a solid-phase extraction adsorbent for the separation and preconcentration of mercury (Hg) was investigated. Hg2+ was found to be quantitatively adsorbed onto graphene within pH 6.0-8.0, and then completely eluted with 4.0 mL of nitric acid/methanol (1:1, v/v) solution at a flow rate of 2.0 mL min-1. A new method using a microcolumn packed with graphene as a sorbent was developed for the preconcentration of trace amount of Hg2+ prior to its determination by hydride generation atomic fluorescence spectrometry. Under the optimum experimental conditions, the detection limit of this method for Hg2+ was 5.0 ng L-1, with an enrichment factor of 15.0, and the relative standard deviation was 3.5% at the 1.0 μg L-1 Hg2+ level. The method was then applied for the determination of trace amount of Hg2+ in water samples with satisfactory results. [ABSTRACT FROM AUTHOR]

Silica-coated magnetic graphene nanocomposite (designated Fe3O4@SiO2/graphene) was synthesized and applied for preconcentration of Cd in different water samples. The extraction process was achieved in a single step by mixing the chelating agent, adsorbents and water samples via ultrasound-assisted action. The magnetic adsorbents were isolated from sample solution with an adscititious magnet. The eluted metal ions from the adsorbents was analysed by flame atomic absorption spectrometry. The advantages of the new method include short analysis time and simple extraction procedure. Under optimum conditions, the relative standard deviation of 300.0 μg L-1 Cd was 4.54%. A concentration factor of 25.0 and the detection limit of 0.54 μg L-1 for Cd was obtained. Satisfactory recoveries (90.5-98.5%) were achieved in four real environmental water samples. [ABSTRACT FROM AUTHOR]