In this paper, ionic liquid (IL)-coated magnetic Fe(3)O(4) nanoparticles (NPs) as an adsorbent of mixed hemimicelles solid-phase extraction (SPE) was investigated for the preconcentration of polycyclic aromatic hydrocarbons (PAHs) from environmental samples. Due to the high surface area and excellent adsorption capacity of the Fe(3)O(4) NPs after modification with ILs, satisfactory extraction recoveries can be achieved with only 80 mg Fe(3)O(4) NPs, 50 mg IL, 300 mL solution at pH = 10 and 10 min for equilibration. A comprehensive study of the adsorption conditions such as the amount of Fe(3)O(4) NPs and ILs, the solution pH, ionic strength, standing time, breakthrough volume, and desorption solvents was presented. The extraction ability of different coating agents, such as 1-hexadecyl-3-methylimidazolium bromide (C(16)mimBr), 1-decyl-3-methylimidazolium bromide (C(10)mimBr) and cationic surfactant cetyltrimethylammonium bromide (CTAB) was also compared. Under the optimized conditions, the recoveries for the water samples analysis were between 76 and 105% with relative standard deviations (RSDs) ranging from 3.9 to 6.9%, and the recoveries for soil samples were between 73 and 104% with RSDs ranging from 1.0 to 6.3%. In this method, only a small amount of C(16)mimBr (50 mg) and Fe(3)O(4) NPs (80 mg) was needed to obtain satisfactory recoveries.
Image reconstruction from cone-beam projections collected along a single circular source trajectory is commonly done using the Feldkamp algorithm, which performs well only with a small cone angle. In this report, we propose an error-reduction-based algorithm to increase the cone angle by several folds to achieve satisfactory image quality at the same radiation dose. In our scheme, we first reconstruct the object using the Feldkamp algorithm. Then, we synthesize cone-beam projection data from the reconstructed volume in the same geometry, and reconstruct the volume again from the synthesized projections. Finally, these two reconstruction results are combined to reduce the reconstruction error and produce a superior image volume. The merit of this algorithm is demonstrated in numerical simulation.
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