| Polycyclic aromatic hydrocarbons(PAHs), which contain two or more fused aromaticrings, are a kind of typical persistent organic pollutants. They exist widely in various kinds of media of the environment, and most of PAHs are carcinogenic, mutagenic, and teratogenic. As their continually migration, the PAHs can enter the body of human through the respiratory tract, the skin, and the gastrointestinal tract, which greatly threaten people's health. Thus, monitoring the PAHs of the environment, has been attracted widespread attention. At present, the technology of using moss as a passive sampler to monitor the PAHs, is simple, convenient and economic and has been widely used. But the matrix of moss is very complex, and the content of PAHs is extremely low, which cause a lot of problems in the analysis process. In order to overcome these difficulties, a rapid and simple method for the determination of PAHs in mosses is established using ultrasonic assisted extraction and gas chromatography tandem mass spectrometry(GC-MS/MS).In order to extract the PAHs in the moss samples, the extraction effects of ultrasonic assisted extraction and soxhlet extraction had been compared, and then the process of extraction(sample status, extraction solvent, extraction time) had been optimized to achieve the best extracting effect of the extraction method. The efficiency of ultrasonic assisted extraction was 1.1% to 25.0% higher than soxhlet extraction for the lower ring PAHs. For larger PAHs, the ultrasonic assisted extraction efficiency was 9.3% to 18.2% lower than soxhlet extraction. The soxhlet extraction generally need to extract more than 24 hours and the solvent dosage is relatively larger, while ultrasonic assisted extraction only need about half an hour and 40 mL solvent. So, in this experiment, the ultrasonic assisted extraction method was selected to extract the PAHs in moss samples. When the moss samples were smashed and the extraction time was extended to 30 min using dichloromethane as solvent extraction, the extractioneffect of 16 kinds of polycyclic aromatic hydrocarbons reachedthe maximum value.In order to improve the accuracy and sensitivity of the gas chromatography tandem mass spectrometry, the parent-product ions and the best collision energy of PAHs were chosen in the paper. In this study, under the premise of 16 kinds of PAHs reached basic separation, the analysis time of GC-MS/MS was tried to be compressed by optimizing the temperature program, and the separation time was compressed to 32 min successfully. Compared with gas chromatography mass spectrometry(GC-MS) method, the signal to noise ratio(S/N) of 16 PAHs were raised more than 3 times. The final instrument detection conditions were as follows: The sample extract(1 ?L) was injected in the splitless mode onto AB-5MS capillary column(30 m × 0.25 mm × 0.25 ?m), and high purity helium was used as the carrier gas at a constant flow rate of 1.0 mL/min. The injector temperature was 300 ?. The oven temperature program was set as follows: holding for 2 min at 70 ?, then 10 ?/min to 300 ? and holding for 7 min. The transfer line was set at 280 ?. The ionization energy was 70 e V, and the ion source temperature was 260 ?. Tandem mass spectrometry was operated in selective reaction monitoring(SRM) mode and the solvent delay time was 5 min.The ultrasonic assisted extraction couple with GC-MS/MS method was applied successfully to determinate the PAHs in moss samples. The total concentration of 16 PAHs were from 500.0 to 781.6 ng/g, and naphthalene, phenanthrene, pyrene and fluorine were the main components, which accounted for 57.2 to 62.2% of the total. In the linear calibration range, the coefficients of linear correlation were greater than 0.9992 for all analytes. The method detection limits(LOD) were from 0.1 to 2.0 ng/mL, the recoveries ranged from 56.8% to 109.0%, and the relative standard deviations were in the range of 1.86% to 9.04%.When the samples contained large amounts of impurities, it would affect the efficiency of GC-MS/MS. Therefore some simple attempts have been made for the purification process in the subsequent experiment. A polystyrene bonded graphene oxide material was synthesized, and was applied to purify the PAHs in the mosses. After purification, the impurity peak decreased, and the background value reduced. The recoveries were not high, which ranged from 72.7% to 91.4%. |
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