New Techniques For Solid Phase Extraction Of Perfluoroalkyl Acids Baced On Functionalized Nanomaterials

Fluorinated organic pollutants are a class of organic pollutants that have attracted much attention.It is reported that fluorinated organic pollutants are harmful to organisms and humans owing to their toxicity and bioaccumulation,and widely available in the environment due to the large-scale use of industrial production and environmental migration,causing environmental and health crisis.Perfluoroalkyl acid pollutants（PFAAs）are a category of typical Fluorinated organic pollutants with a high detection rate in the environment.In view of this,monitoring the concentrations of PFAAs in environmental water samples is of great significance.Consequently,owing to the low concentrations of PFAAs and complex matrix effect,the sample pretreatment procedure is indispensable prior to chromatographic analysis.In this paper,a variety of functional adsorbent materials have been developed for solid-phase extraction technology by means of the designable characteristics of covalent organic framework materials（COFs）and the fluorine-containing characteristics of fluorinated carbon nanotubes（F-CNTs）,and combined with high performance liquid chromatography-tandem mass spectrometry（HPLC-MS/MS）to quantify PFAAs in environmental water samples.The specific research content is as follows:Research 1:Based on the structural characteristics of carboxyl and sulfo groups contained in PFAAs,the new amino-functionalized magnetic covalent organic frameworknanocomposite（Fe₃O₄@[NH₂]-COFs）wasdesigned.1,3,5-tris（4-aminophenyl）benzene,terephthalaldehyde and its derivative bearing azide group were skillfully chosen as building blocks to generate the amino-modified COF shell on the surface of Fe₃O₄.Fe₃O₄@[NH₂]-COFs was prepared at room temperature and served as an adsorbent for magnetic solid phase extraction（MSPE）to enrich PFAAs in environmental water samples.The morphology,structure and properties of Fe₃O₄@[NH₂]-COFs were investigated by various characterisation techniques,such as Fourier-transform infrared（FT-IR）spectroscopy,scanning electron microscopy（SEM）and X-ray photoelectron spectroscopy（XPS）.The adsorption mechanism between the material adsorbent and PFAAs was explored.The results proved that hydrophobic interaction and electrostatic interaction made the main contribution to improve the extraction efficiency of PFAAs.Various parameters that affect the extraction performance of the target PFAAs by MSPE have been studied in detail,such as the type and volume of the analytical solution,the ammonia content of the analytical solution,the amount of adsorbent,the p H of the sample and the adsorption time.The detection method,using Fe₃O₄@[NH₂]-COFs-based MSPE combined with HPLC-MS/MS was established to realize the enrichment detection of PFAAs in environmental water samples.The developed method had low detection limits(0.05-0.38 ng L^-1),quantification detection limits(0.16-1.26 ng L^-1),wide linear range(10-10000 ng L^-1)and R²（≥0.9990）.The enrichment factor（EFs）is between 36 and 59.With good RSD of inter-day（3.7%-9.2%）and batch-to-batch RSD（2.8%～9.1%）,the recovery rate of PFAAs in actual environmental water samples is 72.1%-115.4%,and the RSD is 0.4%-9.8%.Research 2:Due to the unique structure of PFAAs that replace hydrogen atoms with fluorine atoms,Fluorinated carbon nanotubes（F-CNTs）have become potential adsorbents for the Fluorous solid phase extraction（FSPE）of PFAAs in environmental water samples.Fluorous-fluorous,hydrophobic and hydrogen bonding interactions between F-CNTs and PFAAs enhanced the adsorption capacity of F-CNTs.The recovery rate of PFAA is 18.4%-60.0%higher than that of carbon nanotubes.Various parameters that can influence the extraction performance of FSPE for target PFAAs were investigated in detail.,including desorption solution,p H value of sample solution,volume of the desorption solution,the ammonia content of the desorption solution,the amount of adsorbent,the flow rate of the water sample,and so on.Under the optimized conditions,wide linear range(0.2-2000 ng L^-1)and R²（0.9990-0.9999）,and good repeatability（2.1-9.4%）and good reproducibility 2.8-8.3%were obtained.The limit of detection（LOD）and limit of quantification（LOQ）were in range of 0.012-0.049 ng L^-1and 0.040-0.163 ng L^-1.The recovery rate and RSD were in range of 71.8%-116.0%and 1.4%-9.9%.F-CNTs provided a good choice for enrichment and analysis of other Fluorinated organic pollutants from a variety of samples.