Covalent organic framework modified nickel foam adsorbents for dispersive micro-solid phase extraction of polycyclic aromatic hydrocarbons from Chinese herbal medicines

Sixteen polycyclic aromatic hydrocarbons (PAHs) contaminants in Chinese herbal medicines were determined based on metal covalent organic framework (MCOF) combined with gas chromatography-mass spectrometry (GC–MS) and dispersive micro-solid phase extraction (D-μ-SPE) methods. The MCOFs were constructed by using 2,5-dihydroxy-1,4-benzenedicarboxaldehyde (Dt) and 4′,5′-bis(4-aminophenyl)-[1,1′′,2′,1′′-triphenyl]-4,4′′-diamine (BAPTPDA) as monomers. The morphological structures were characterized by scanning electron microscopy and the stability of BAPTPDA-Dt was characterized by various techniques such as fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and thermogravimetric analysis. The results showed that nickel foam (NF) was covered by covalent organic frameworks and that NF@COF (BAPTPDA-Dt) exhibited excellent stability. The adsorption capacity of MCOF for PAHs ranged from 30.8 to 262.5 mg g−1. A number of parameters that might affect the extraction efficiency of D-μ-SPE were optimized, which resulted in a more efficient and time-saving extraction process (2 min) with less consumption of organic reagents (1 mL). The qualitative and quantitative analysis of the 16 PAHs was performed by GC–MS with the limits of detection ranging from 0.55 to 5.93 µg/L. A wide linear range (20–2000 µg/L) was achieved with coefficient of determination (R2) between 0.9930 and 0.9994. The recoveries for the three spiked sample concentrations (20, 200 and 500 µg/L) varied from 80.8 % to 126.7 %. The relative standard deviations (RSDs) for PAHs were all less than 7.79 %. The total contents of the 16 PAHs contained in the five herbs (Gardenia, Plantain Seed, Rhizoma Alismatis, Evodia Fruit and Peucedani Radix) were in the range of 308–1070 µg kg−1. The results indicated that the established method has significant repeatability and reproducibility.