| Perfluorinated compounds(PFCs)are widely present in soils,water bodies and organisms.They are characterized by persistence,pollution,bioaccumulation and refractibility.Perfluorooctane sulfonic acid and its salts have been classified as persistent organic Pollutants(POPs),and paid attention at home and abroad.In this paper,four kinds of perfluorinated compounds were used to study the environmental samples pretreatment and instrumentation of PFCs.The effects of different molecular weight PFCs,inorganic salts,organic matter and removal characteristics of PFCs by nanofiltration membrane were studied by small cross-flow nanofiltration membrane filtration.Through the experimental study,the following results are obtained:(1)The optimum solid phase extraction conditions were as follows: the activation solution was ammonia water and deionized water,the drip rate was 2 drops/s,the water sample velocity was 2 drops/s,the eluent was 40% methanol water(pH = 5),the drip rate is 2 drops/s,the eluent is 0.1% ammonia water,the drip rate is 1 drop/s,the solvent volume were 4mL for all.Trace PFCs in water were determined by ultra performance liquid chromatography-mass spectrometry(UPLC-MS/MS).The detection limit of the method was 0.06ng/L-0.22ng/L,and the recoveries were 73.1%-91.3%.The relative standard deviation was 7.4%-14.3%.The results show that the method is in good linearity,it is accurate and can meet the requirements of trace PFCs analysis of environmental water samples.(2)Pure water,inorganic salts(sodium chloride,calcium chloride),organic matter(Sodium alginate,bovine serum albumin,humic acid),inorganic salts and organic solutions were mixed with PFCs standard substance to form a certain concentration of PFCs raw water,The removal characteristics of PFCs under these water conditions were studied.The study found that the following factors affect the removal of PFCs by nanofiltration membranes:(1)Under pure water conditions,the screening effect of nanofiltration membrane on perfluorooctane sulfonic acid(PFOS)was stronger than that of perfluorobutyl sulfonic acid(PFBS)due to the higher relative molecular weight.(2)Under the condition of adding inorganic salt,the double layer of the membrane is compressed,the decrease of the electrostatic repulsion leads to the decrease of the rejection,the shrinkage of the membrane hole leads to the increase of the interception rate.The calcium ion in the calcium chloride causes the bridging effects between PFCs,PFCs and membrane,the pollutant volume increase,improving the rejection rates.Under the combined effect,the rejection rate of PFOS was higher than that of pure water,and the rejection rate of PFBS was decreased than that of pure water.(3)In the presence of organic matter,SA and HA increase the membrane potential,they increase the rejection rate of PFCs by enhancing the electrostatic repulsion.BSA mainly through its complex spatial structure and larger molecular weight to adsorb PFCs on its surface to improve the rejections of PFCs on membrane,the retention rate of PFOS was higher than that of pure water.The rejection rate of PFBS was basically the same as that of pure water.(4)When the inorganic salt and organic matter coexist,the change of electrostatic repulsion caused by the change of membrane potential is the main effect of membrane on PFOS and PFBS,and the radium of membrane holes shriked.Compared to(2),calcium ions will also cause organic molecules complexation due to the exist of a certain amount of aminos?carboxyls and hydroxyls in BSA? SA and HA.In conclusion,the rejection rate for PFOS was higher than that of pure water,While the rejection rate for PFBS retention rate is basically the same as pure water. |
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