Determination Of Methyl Tert-Butyl Ether In Soil By Head Space Microextraction Gas Chromatography And Mass Spectrometry

Object:To establish a novel method to detect the concentration of methyl tert-butyl ether in soils,which was named head space solid phase microextraction gas chromatography associated with mass spectrometry.To make a survey and comment on the soil pollution by methyl tert-butyl ether in Shenzhen,Peking and Nanning.Method:Head space solid phase microextraction was applied to the pretreatment of soil samples,and the extraction conditions including extraction coating,solution,stirring speed,extraction time and extraction temperature were optimized.Agilent7890A-5975 C gas chromatography-mass spectrometry was applied to determine methyl tert-butyl ether extracted on the extraction fiber,with a capillary column of DB-5MS(30 m×0.25mm×0.25 ?m),and the parameters of injection,procedure of temperature and mass spectrometry were optimized.Static-head space gas chromatography was employed in determining the blank soil sample which was turned into Standard samples by spiking with the standard solution of methyl tert-butyl ether.Blank test and recovery test were carried out for the quality monitoring,and the precision and accuracy were test.Soil samples on the surface of 0-15 cm selected from artery,service station,dryland and paddy field in Shenzhen,Peking and Nanning were analyzed by the method established in this paper,nonparametric test of Tamhane's was applied to estimate the difference of the concentration of methyl tert-butyl ether in soil between different cities or different sampling site.Results: 2.0 g soil was transferred into 20 ml analysis vial which containing 5.0 ml extraction reagent and 2.0 ml methyl alcohol before extraction.The saturated sodium chloride solution was found to be the most effectively extraction reagent,whose extraction efficiency was respectively as 5times,2.7times and 1.7times as that of pure water,saturated potassium chloride and saturated sodium sulfate.For the extraction of methyl tert-butyl ether in soil samples,stirring speed of 400 rpm was the most satisfactory centrifugation condition,since there was no significant change while the stirring speed keeping going up.When the vial was placed in a heating block with the temperature of35 ? for 30 min,the peak area was reached to the most.The response of gas chromatography increased slightly when the extraction time was extension,however,the peak area would decrease obviously at higher temperature.The parameters of gas chromatography and mass spectrometty were optimized as follows: The temperature of inlet was 200 ? and the split ratio was 5:1.The temperature program of oven was 35 ?keeping for 4 min and up to 200 ? at a rate of 50 ?/min,remained for 5 min,the flow of the carrier gas was 1.0 ml/min.The mass spectrometty ion source was electron impact(EI)with the energy of 70 e V,the mass spectrometty was performed in a selected ion mode with the quantitation ion was m/z 73.The temperature of ion source,quadrupole and transfer line were 200 ?,150 ? and 230 ? respectively.The method established in this paper performed well with respect to a correlation coefficient of 0.9992,a lower detection limit of 0.0075 ?g/kg,and the calibration equation was Y=5090.9X+35.269,over the concentration range of 0.0075 ?g/kg~5 ?g/kg.The recovery test showed that the mean recovery values were from 84.5% to 98.3%,intra-day precision was 4.3%~6.7%,inter-day precision was 8.9%~9.2%.The results of field application showed that methyl tert-butyl ether was detectable in all four types surface soil samples of artery,service station,dryland and paddy field from three cities in China.However the concentrations were at a lower level,the rang of concentration was 0.0100 ?g/kg~0.072 ?g/kg,the data showed that concentration of metyltert-butyl ether in soil from artery was generally at a higher level,with the mean concentration of(0.0190±0.0193)?g/kg for Shenzhen,(0.0117±0.0090)?g/kg for peking and(0.0104±0.0126)?g/kg for Nanning,respectively.However,the highest and the lowest concentration were coming out to be in the dryland soil from Shenzhen and Nanning,namely(0.0217±0.0104)?g/kg and(0.0074±0.0050)?g/kg.Whereas there was no significant difference of the concentration of methyl tert-butyl ether in soil samples among different cities,neither among different sampling site.Conclusion: By applying the technology of head space solid phase microextraction to the pretreatment,the process of extraction,separation and concentration was simplified,and the matrix effect was significantly decreased as well.Associated with gas chromatography and mass spectrometry,the established method was easy for handling,and showing a good precision,accuracy and sensitivity.It could be practical for the monitoring of methyl tert-butyl ether in soil.