Study On The Pretreatment Method For Nitrobenzene In The Soil And The Method Evaluation

Nitrobenzene is an important chemical raw material widely used in fuel, medicine, explosives, pesticides and polymer chemistry industry. It is one of the priority control toxic organic pollutants established by US EPA, EC as well as China. Its toxicity is usually 20 to 30 times more than other toxic compounds. There is suspicion that it contributes mutagenicity and carcinogenicity to the organisms and causes neurological symptoms, anemia and liver disease. If contacted it for a long period of time it is seriously harmful to human beings, animals and plants. Nitrobenzene in the environment is mainly generated from chemical plants, Ranliaoan wastewater and emissions, in particular; the discharge of sewage from Ranliaoan aniline containing high concentrations of nitrobenzene. It is possible to contact the material (nitrobenzene) during the process of usage, handling and transporting the raw material and accidents happen during transportation and storage will also create serious nitrobenzene pollution.Many developed countries commit large amount of manpower and material resources into basic research and application study on the characteristic, the present pollution situation, the environmental migration transformation behavior, the ecology toxic and so on. They include the volatilities, the adsorption, the biodegradation, the non-biodegradation (hydrolisis, photolysis and so on),the biology concentrates and so on. There are also environmental behavior researches on the nitrobenzene in atmosphere, water, soil and other medium. However; researches in this field is relatively new to us. There is certain disparity between us and the other developed countries. Since there is no method in GB15618—1995 to analyze nitrobenzene in soil, it's necessary to establish a fast and convenient analyzing method to detect nitrobenzene in the soil.At present, with the help of advanced computer capabilities, significant improvements to identify complex multi-components fast and convenient have been achieved by utilizing the chromatograph parsing technique. GC-ECD is generally used to measure nitrobenzene both domestically and abroad. But the reports on carrying out the quantitative analysis with GC-MS are extremely rare. We were able to use GC-MS in quantitative analysis to improve the accuracy; One problem happens so often is that the gas phase chromatography countermeasure and the tested sample have the same retention time, so they show up at the identical root chromatographic column. Particularly, it tends to create false positive results for the unknown pollutant samples, thus reducing the analysis accuracy. Along with the development and progress of MS technology, mass analyzer's stability and the sensitivity have been improved significantly. The MS analyzer may also carry on choice of ion scanning method (SIM); in this case, the MS spectrum used as detector makes the qualitative measurements to be more accurate. Current studies using GC-MS in the quantitative analysismore accurate qualitative measurements are achieved with the help of MS used as detector which may effectively solve or significantly reduce the noise problem stated above.The environmental pollution has been concerned by many countries in the world. However; the environment varies from place to place. There are lots of Countermeasures existed in each environment, usually in order to satisfy the trace analysis request the sample must undergo the pretreatment. Therefore, the demand for environment sample pretreatment technology is getting higher and higher. Although traditional pretreatment method like rope withdraws, the extraction efficiency is high, but massive resolvers have to be consumed which can create additional pollution to the environment. Other problems like the extraction time is long, it is labor intensive and possible to have the sample lost make it not being able to fulfill the modern parsing technique request. Statistics indicated that in the chromatograph analysis the time used in the sample preparation process approximately accounts for 70% of the entire analysis time, only 10% of the time is used for sample analysis. Obviously, the sample pretreatment process in the entire parsing process is the weakest link and it is the key step to decide the working efficiency. Even there is automatic pretreating device for sale in the market, but it is too expensive to be economic feasible to be used in ordinary laboratory. Therefore, in order to substitute traditional method it is the necessary to improve and optimiz the preparation method for chromatograph analysis sample.The ultrasonic extract, using the intense cavitation caused by supersonic wave radiation pressure, the entire process can be completed in 400s. It refines each material, manufactures emulsion and accelerates the targeted ingredient entering the resolver, thus enormously increasing the extraction yield. The ultrasonic wave produces many second-order effects: the mechanical vibration, the disturbing effect, the high acceleration, the emulsification, the proliferation, crushing, the agitation and so on. Those effects have increased the material molecular transport frequency and the speed and increased the resolver penetrating power, also favor the shift of the targeted ingredient and the extraction. It is one highly effective and fast sample pretreatment method. Because the nitrobenzene structure is quite stable, may obtain the extract using the ultrasonic.This research studied the rapid analysis method: how to use the ultrasonic extraction technology - GC-MS determination the nitrobenzene in soil. First, We chose three representative kinds of soil: The clay, the sandy soil and the loam as the experimental objects. Use of ultrasonic extraction technology, add known quantity of nitrobenzene then try to do extraction recovery in the experiments. Considering both the extraction effect and the influence to the human body and the environment, make sure that Chloroform is the best extraction solvent of the six different resolvers: The normal hexane, the cyclohexane, the methylene chloride, the chloroform, the benzine, MTBE. Choose five factors: Said that the type quantity, the Canadian scalar, the extracting agent join volume, supersonic time, anhydrous Na₂SO₄ to join the quantity according to the extraction recovery of nitrobenzene added previously, designs orthogonal test and determines the best conditions of ultrasonic extraction. With experimental result's Contrastive analysis, it was determined the best conditions of ultrasonic extraction are: The resolver amount used is 10mL, said that the type quantity is 3g, adds the scalar is 3uL, the supersonic time is 10min, anhydrous Na₂SO₄ joins the quantity is 5g.Finally, we found a fast and convenient pretreatment technology for nitrobenzene in soil: Weighing accurate 3g of soil sample, add anhydrous Na₂SO₄ of 5g, add accurate of 10ml chloroform, by ultrasonic extraction technology, put them all into the ultrasonic bath and run for 10 mins. Extract liquid filters through 0.45μm membrane filters to agilent bottle, then analyzed by GC-MS.At last, the uncertainty of measurement of the method was evaluated according to the "People's Republic of China National Metrology Technical Specification" (JJF1135-2005) and the relevant standards on "Uncertainty of Measurement Evaluation and Indicate".This method paranitrophenyl returns-ratio is about 92%. The nitrobenzene detection limit is 0.015ug/L. The method accuracy is 2.16%. When comparing the ultrasonic extract experiment with the Soxhlet method analysis, the following conclusions can be made: Returns-ratio both are quite comparable and the accuracy of the former is higher than that of the latter. The ultrasonic extract consumes lower quantity resolver, reduces the sample preparation time greatly and causes the makings to unite with the analysis method low examination limits. It is highly specific and the high accuracy characteristic is truly manifested in this method. At the same time, this method not only can satisfy the trace analysis request, but also can be used in the heavy molecular weight's sample analysis. Based on the real life samples' analysis, it is proven that this method is an accurate, convenient and practical way to analyze the nitrobenzene in the soil.In the end, according to GB/T15481-2000 (the general request to examines and calibrates the laboratory ability) requests: laboratory must perform the Uncertainty evaluation work in the standard certificate, in the examination report and in the technical paper. Anything involved in the measurement results, would have to go through the uncertainty analysis based on the "People's Republic of China National Metrology Technical Specification" (JJF1135-2005) It is important to evaluate the Uncertainty of measurement of this method and to identify various sources and parameters that contribute to the uncertainty. Only after doing that, should the quality of the test results can be assured and the improvement of the future test results can be achieved through tightly controlled the known parameters and sources that create the uncertainty.