A new selective and high-capacity magnetic solid phase extraction sorbent was developed for preconcentration of trace amounts of nickel ions prior to their determination by flame atomic absorption spectrometry (FAAS). The sorbent was prepared by immobilization of dimethylglyoxime ligand (DMG) onto magnetic graphene oxide nanoparticles (MGO) coated with surface-active ionic liquid-based surfactant, 1-hexadecyl-3-methylimidazolium chloride ([C 16 MIM][Cl]). The prepared adsorbent (DMG-C 16 MIM/MGO) was characterized by FESEM, TEM, BET, XRD, VSM and FT-IR spectroscopy. The fabricated adsorbent combines the advantages of superior adsorption capability of modified graphene oxide and magnetic separability of magnetic nanoparticles to provide high adsorption capacity, and easy isolation from sample solutions. Several important parameters influencing the extraction efficiency, such as pH, amount of adsorbent, extraction time, elution conditions, sample volume, interfering ions and adsorption capacity were studied and optimized. Applying all optimum conditions in the process, high preconcentration factor of 100, linear range of 0.56-200 µg L -1 , detection limit of 0.16 µg L -1 , and precision (RSD%, n=6) of 1.21%, were obtained for nickel. Following a 2 modification with 1-hexadecyl-3-methylimidazolium chloride and DMG, modified adsorbent selectivity toward nickel ions was raised more than nine-fold compared to the unmodified magnetic graphene oxide. Adsorption capacity within 15 min interaction time based on the Langmuir model was 129.87 and 26.59 mg g -1 for modified and unmodified adsorbents, respectively. The recoveries in case of real samples varied within the range of 96.8-99.2%confirming good performance of the method in various real samples.

An efficient adsorbent, diethylenetriamine-functionalized magnetic graphene oxide nanocomposite (GO-Fe 3 O 4 -DETA), was synthesized through the formation of amide linkage bonds between the amine groups of diethylenetriamine and the oxygen-containing functional groups (e.g., epoxy and carboxyl groups) of graphene oxide. The prepared adsorbent was characterized by scanning electron microscopy, vibrating sample magnetometer and Fourier transform infrared spectroscopy. The synthesized GO-Fe 3 O 4 -DETA was applied as an efficient adsorbent for the simultaneous extraction and preconcentration of trace quantities of lead and cadmium ions from water and vegetable samples. Following extraction, the ions were determined by flame atomic absorption spectrometry. Several important parameters influencing the extraction efficiency, such as pH, amount of adsorbent, extraction time, elution condition, sample volume, interfering ions and adsorption capacity were studied and optimized. Under the optimum extraction conditions, the calibration curves were linear in the range from 1.35 to 110 of Pb(II), and from 1.40 to 120 of Cd(II) in the initial solution. The limits of detection were 0.38 µg L -1 and 0.40 µg L -1 for lead and cadmium, respectively. Precisions, expressed as relative standard deviations, were 1.86% and 2.38% for Pb(II) and Cd(II), respectively. The preconcentration factors were 167 for lead and 150 for cadmium and the maximum adsorption capacity of the modified adsorbent was found to be 172.41 and 59.88 mg g -1 for lead and cadmium, respectively. The recoveries in case of real samples varied within the range of 94.4-103.9% confirming good performance of the method in various water and vegetable samples.

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