The Application Of Magnetic Solid Phase Extraction And Dispersive Liquid- Liquid Micro-extraction For The Determination Of Polycyclic Aromatic Hydrocarbons In Water

Polycyclic aromatic hydrocarbons?PAHs?, refer to compounds with two or more benzene rings with linear, angular or cluster-like arrangement of the fused ring hydrocarbons. With the dramatic increase in coal and oil consumption with the development of industry, PAHs as products of incomplete combustion or pyrolysis of organic materials are widely present in the environment. PAHs are the first to be discovered as substances with carcinogenic, teratogenic and mutagenic effects. Therefore, monitoring of the contents of PAHs in water has great significance. This article has developed two new sample preparation methods for the detection of PAHs in water samples. The thesis is divided into three chapters, the main contents are as follows:Chapter 1: The existing sample preparation methods were summarized, with emphasis on magnetic solid phase extraction, dispersive liquid-liquid micro-extraction and the extraction methods for the analysis of PAHs. Besides, the background and the purpose of this article were described.Chapter 2: A new method for the determination of PAHs by Fe₃O₄@PDA magnetic solid phase extraction-HPLC was established. Core/shell structured magnetic Fe₃O₄@PDA nanoparticles have been successfully synthesized and characterized by FT-IR spectrometer. Parameters affecting the extraction efficiency were investigated in detail, including the amount of adsorbents, p H, salinity, volume of eluent, ultrasonic time and solution volume. The results indicated that the extraction efficiency of PAHs was independent of the ionic strength and solution p H. Under optimum conditions, i.e 80 mg Fe₃O₄@PDA, 4 m L acetonitrile, 250 m L water sample, ultrasonic time 3 min, the extraction yield reached the highest value. Tap water, well water and river water were determined under the optimal extraction conditions. The results indicated that there were no PAHs in the three water samples. Recoveries were in the range of 95%-110%, and the enrichment factors of Phenanthrene and Pyrene were 451 and 455.This method can quickly adsorb and separate the target analytes from sample solutions due to the application of magnetic nanomaterials. The established method has the advantages of simplicity, rapidity and high extraction efficiency.Chapter 3: A p H-dependent fatty-acid-based dispersive liquid-liquid micro extraction-HPLC technique was proposed for the determination of polycyclic aromatic hydrocarbons. The extraction of the target substances was achieved by adjusting the p H of the solution to change the state of n-heptanoic acid. When fatty acid was added to the sample solution, it was suspended on the surface of the sample solution due to its immiscibility with the aqueous solution. Approximately 99.9% of the fatty acid was dissociated into its anion form as an anionic surfactant by adding ammonium hydroxide to the sample solution to achieve a p H higher than its p Ka by at least three p H units?the p Ka of heptanoic acid is 4.78?. After thorough mixing, micelles were formed and hydrophobic analytes were extracted into the micelles?oil in water?. When sulfuric acid was added to the micellar solution to achieve a p H at least three p H units below its p Ka, more than 99.9% of the fatty acid returned to its neutral hydrophobic form. The hydrophobic phase was then separated from the aqueous phase by centrifugation. Parameters affecting the extraction efficiency were investigated in detail, including the type and volume of extraction agent, ammonium hydroxide volume, sulfuric acid volume and centrifugation time. Under optimum conditions, i.e 55 ?L n-heptanoic acid, 50 ?L concentrated ammonium hydroxide, 500 ?L concentrated sulfuric acid; centrifugation time 3 min, the extraction yield reached the higest value. Under the optimal conditions, three kinds of water samples were analyzed and no PAHs were detected. The recoveries were in the range of 80.0-110%. Relative standard deviation of reproducibility experiment was below 4.19%. Compared with the previous methods for the extraction of PAHs, this method required only 6 min with good results. Therefore, the established method is simple, convenient and environmently friendly.