Study On The Separation And Determination Of Seven Monoaromatic Hydrocarbons In Laboratory Waste Water By Gas Chromatography-mass Spectrometry

With the conducting of production,researching and teaching in inspection departments,research institutes and universities,respectively,more and more wastewater had been discharged from laboratory.The compositions of wastewater are extremely complicated,which has a serious impact on ecological environment.As common organic solvents,the Monoaromatic Hydrocarbons（MAHCs）are toxic and harmful pollutants in laboratory wastewater.The national integrated wastewater discharge standard（GB 8978-1996）clearly specifies that the maximum allowable emission concentrations of toluene,ethylbenzene,p-xylene,m-xylene and o-xylene in wastewater are 0.1,0.4,0.4,0.4 and 0.4μg/mL,respectively.Therefore,this study established pretreatment methods of salting-out microextraction and solid-phase extraction for determination the toluene,ethylbenzene,p-xylene,m-xylene,o-xylene,1,3,5-trimethylbenzene and 1,2,4-trimethylbenzene by using gas chromatography-mass spectrometry.The results provided some alternative methods for monitoring MAHCs in laboratory wastewater.The main works and results are as follows:（1）The instrument conditions of gas chromatography and mass spectrometry for toluene,ethylbenzene,p-xylene,m-xylene,o-xylene,1,3,5-trimethylbenzene and1,2,4-trimethylbenzene were optimized.The DB-5MS capillary column（30 mm×0.25mm×0.25μm）was used.The temperature of inlet,EI source and quadrupole were220℃,240℃ and 150℃,respectively.The electron energy was 69.9 eV with electron multiplier voltage of 1741 V.The carrier gas was helium with column flow rate of 1 mL/min.The sampling depth was 1.5 mm.The solvent delay was 3.5 min,and the split ratio was 30:1.The temperature program:the initial temperature was45℃ and keeping for 3 min,then warming up to 70℃ at 3℃/min.Finally warming up to 200℃ at 30℃/min and keeped for 2 min.（2）Using chloroform as extractant and ammonium chloride as salting-out agent,the method of salting-out microextraction-gas chromatography-mass spectrometry had been established for determination toluene,ethylbenzene,o-xylene,m-xylene p-xylene,1,3,5-trimethylbenzene and 1,2,4-trimethylbenzene in laboratory wastewater.When the amount of chloroform was 25μL,the amount of ammonium chloride was0.2 g,and the centrifugation was performed at 5000 r/min for 5 min,the MAHCs in 1mL of water sample could be well extracted and enriched.The multiple was 40 times.Under the optimized conditions of extraction and determination,the linearity of the seven MAHCs were good with peak area,and the correlation coefficients were greater than 0.993.The detection limits were between 0.01⁰.5 ng/mL.The relative standard deviation were between 1.8⁴.1%.The laboratory wastewater of Chengdu University of Technology（CDUT）and Dongfeng river water were determinated.The results met the maximum allowable emission concentration of MAHCs in the national comprehensive waste water discharge standard.At the same time,a recovery experiment was performed.The recovery rates of the seven MAHCs in the laboratory wastewater and the Dongfengqu river water were between 93.0%¹11.1%and96.9%¹10.5%,respectively.And the relative standard deviations were between2.2%⁴.5%and 2.9%⁵.7%,respectively.（3）In order to further increase the enrichment factor and reduce the detection limit of the method,the Magnesium-Aluminum Layered Hydroxide（Mg-Al-LDH）intercalated by Sodium Dodecyl Benzene Sulfonate（SDBS）was used as a solid-phase extractant（Mg-Al-SDBS-LDH）.Under the condition of chloroform as eluent,the method of solid-phase extraction-gas chromatography-mass spectrometry had been established for determination seven MAHCs in wastewater.When the Mg/Al-SDBS-LDH was 1 g,the extraction time was 5 min,and elution was performed with 4 mL of chloroform for 3 min,the MAHCs in the 500 mL water sample could be well extracted.The enrichment factor was 125 times.Under the optimized conditions of extraction and determination,the linearity of the seven MAHCs were good with peak area,and the correlation coefficients were greater than0.995.The detection limits were between 0.0005⁰.005 ng/mL.The relative standard deviations were between 3.1⁶.6%.The laboratory wastewater of CDUT and Dongfeng river water were determinated.The results met the maximum allowable emission concentrations for seven MAHCs in the national comprehensive wastewater discharge standard.The recovery rates of the seven MAHCs in the laboratory wastewater and the Dongfengqu river water were between 84.0¹12.6%and81.8%¹09.0%,respectively.And the relative standard deviations were between4.5%⁸.8%and 3.5%⁹.6%,respectively.The established method satisfied the detection requirement for ultra-trace MAHCs in waste water.（4）In this study,Graphene oxide（GO）and GO/Mg-Al-LDH were prepared by the modified Hummers method and the steady-state co-precipitation method,respectivety.The optimal preparation process were as follows:under the concentrated sulfuric acid,the graphite was pre-oxidized with K₂S₂O₈ for 4 h at 80℃,then the graphite was slowly oxidized with KMnO₄ for 4 h at 35℃.Finally,a flake-like GO suspension was obtained by ultrasonic stripping.100 mL of Magnesium-Aluminum mixture（15.4 g Mg（NO3）₂·6H₂O,7.5 g Al（NO₃）₃·9H₂O）was added to an aqueous solution with 2 mL of GO suspension at the pH of 10±0.5 and temperature of 60℃.After continuing to react for 2 h,GO/Mg-Al-LDH composite was obtained.The SEM,XRD,FT-IR,and TG-DTA characterization of the materials prepared under the optimal route were performed.The results show that surface of GO/Mg-Al-LDH had a large number of active functional groups as the adsorption site of MAHCs.（5）Using GO/Mg-Al-LDH as solid-phase extractant and chloroform as eluent,the method of solid-phase extraction-gas chromatography-mass spectrometry had been established for determination seven MAHCs in wastewater.When the amount of material was 1.5 g,extraction time was 6 min,and 2 mL of trichloromethane eluted for 3 min,the MAHCs in 500 mL water sample could be extracted well,and the enrichment factor was 250 times.Under the optimized conditions of extraction and determination,the linearity of the seven MAHCs were good with peak area,and the correlation coefficients were greater than 0.995.The detection limits were between0.0005⁰.005 ng/mL.The relative standard deviations were between 3.2%⁷.1%.The laboratory wastewater of CDUT and Dongfeng river water were determinated.The measurement results met the maximum allowable emission concentration of MAHCs in the national comprehensive wastewater discharge standard.The recovery rates of the seven MAHCs in the laboratory wastewater and Dongfengqu river water were between 87.0¹07.0%and 83.0%¹10.0%,respectively.And the relative standard deviations were between 3.9%⁸.5%and 3.7%⁹.4%,respectively.Using GO/Mg-Al-LDH as solid-phase extractant,the enrichment ratio of MAHCs increased greatly.Moreover,a large number of functional groups on the surface of material could made better adsorption performance for MAHCs.The established analytical method could meet the measurement requirement of ultra-trace MAHCs in complex system.