Preparation and application of bimetallic coordination cluster Cu7Mn2 for dispersive solid phase extraction of polycyclic aromatic hydrocarbons in lettuce

In this study, bimetallic coordination cluster Cu 7 Mn 2 was synthesized by solvent thermal method and based on the features of large specific surface area, rich adsorption sites, the material was applied for the dispersive solid-phase extraction of pyrene, fluoranthene , phenanthrene and fluorene in lettuce followed by high performance liquid chromatography analysis. The sythesized Cu 7 Mn 2 cluster was characterized by Fourier transform infrared spectroscopy , scanning electron microscopy, thermogravimetric analysis , hydrophobicity and nitrogen adsorption-desorption experiments. The adsorption kinetics and adsorption isotherms were carrued out. Then, the adsorption mechanism was speculated to be the coexistence of π − π stacking, hydrophobic interaction and N−H···π interaction. The adsorption experimental results indicated that Cu 7 Mn 2 cluster had better adsorption properties for pyrene, fluoranthene, phenanthrene, fluorene than Cu cluster and Mn cluster. The extraction conditions such as the kind and volume of desorption solvent, the adsorption and desorption time, the sample volume and salinity were investigated. Under the optimal conditions, a DSPE-HPLC method was developed for the determination of pyrene, fluoranthene, phenanthrene and fluorene in lettuce. The linearities were 0.5 − 1000 μg/kg for phenanthrene, fluorene and 3−1000 μg/kg for pyrene, fluoranthene (R 2 >0.99), respectively. The limits of detection (LODs, S/N = 3) and the limits of quantification (LOQs, S/N = 10) were in the ranges of 0.12−0.81 μg/kg and 0.40 − 2.7 μg/kg, respectively. The intra- and inter-day precisions (RSDs) were less than 2.9% and 4.0%, respectively, and the recoveries were in the range of 94.9% − 101.1%. The established DSPE-HPLC method has been proven to be accurate for the analysis of four polycyclic aromatic hydrocarbons in lettuce samples.