Preparation of phenyl-modified magnetic silica as a selective magnetic solid-phase extraction adsorbent for polycyclic aromatic hydrocarbons in soils

Accurate analysis of polycyclic aromatic hydrocarbons (PAHs) in soils remains a challenge due to the complexity of sample matrices. In this paper, phenyl-modified magnetic mesoporous silica (Fe3O4@mSiO(2)-Ph-PTSA) was synthesized with p-toluenesulfonic acid (PTSA) as the catalyst and used as a selective adsorbent for the clean-up of PAHs extracted from soils. The material prepared without PTSA as the catalyst (Fe3O4@mSiO(2)-Ph) was synthesized for comparison. The synthesized materials were first systematically characterized and evaluated. It was found that the grafting amount of the phenyl group onto Fe3O4@mSiO(2)-Ph-PTSA was higher than that onto Fe3O4@mSiO(2)-Ph. The extraction efficiency obtained by extracting PAHs from the extracted soil matrix solution demonstrated that Fe3O4@mSiO(2)-Ph-PTSA possessed a much higher extraction efficiency than that of Fe3O4@mSiO(2)-Ph, which can be attributed to the greater amount of phenyl groups grafted on Fe3O4@mSiO(2) in the presence of the PTSA catalyst. Moreover, contrast experiments showed that Fe3O4@mSiO(2)-Ph-PTSA displayed higher selectivity towards PAHs than towards n-alkanes and that the Tr-Tr interaction played a key role in the adsorption process. In the presence of the soil extract matrix, the parameters affecting the extraction efficiency of Fe3O4@mSiO(2)-Ph-PTSA for PAHs were optimized. Under the optimal conditions, coupled with pressurized liquid extraction and gas chromatograph-mass spectrometer, the proposed method for the determination of PAHs in soils was linear in the range of 5-500 ng g(-1), and the correlation coefficients (R) ranged between 0.9994 and 0.9999. The limits of detection (LODs) and limits of quantification (LOQs), which were based on signal-to-noise ratios of 3 and 10, respectively, were in the range of 0.07-0.41 ng g(-1) and 0.24-1.37 ng g(-1). The developed method displayed a better clean-up effect than that for silica gel column method, and the matrix effect markedly decreased compared to that of the uncleaned condition. Finally, the developed method was successfully applied for the detection of PAHs in environmental soils, and the data were consistent with the results obtained by the silica gel column method. The analytical results were also consistent with those for the real environment. (C) 2018 Elsevier B.V. All rights reserved.