液液微萃取-甲基衍生化/气相色谱法对水中氯代酸除草剂的测定

Determination of Chlorinated Acid Herbicides in Water by Liquid-liquid Microextraction-Methyl Derivatization/Gas Chromatography with Electron Capture Detection

在pH大于12的条件下使水样中的氯代除草剂全部水解为盐，用正己烷和甲基叔丁基醚混合溶剂提取有机杂质，再在酸性条件下经5mL甲基叔丁基醚提取，重氮甲烷甲基衍生化30min后用带微电子捕获检测器的毛细管气相色谱分析，以4，4’-二溴八氟联苯为内标物进行定量。茅草枯、麦草威、2，4-D、五氯苯酚的质量浓度分别在5．0—500、1．0～200、5．0～500、0．5～100ug／L范围内与色谱峰面积呈良好的线性关系（r=0．9945～0．9980），检出限分别为1．0、0．5、1．0、0．1ug／L。用该法测定南京玄武湖水样中的茅草枯，其质量浓度为7．1ug／L，4种被测组分在高、中和低添加水平下的回收率分别为102％～105％、96％-110％、87％-109％。同时建立了一种生产重氮甲烷的新原料——N-亚硝基-N-甲基脲的简易方法。

Aqueous sample of chlorinated acid herbicides was hydrolyzed to salts under pH more than 12 and cleaned up by hexane - MtBE mixture, then acidified and extracted with 5 mL methyl tert-bu- tyl ether（MtBE）. The chlorinated acid herbicides were derivatized by diazomethane for 30 rain. The target methyl esters were determined by capillary column gas chromatography with u-ECD. Quantitative analysis was carried out by using 4, 4＇-dibromooctafluorobiphenyl as an internal standard. A good linearity（r =0. 994 5 -0. 998 0） was obtained in the range of 5.0 -500, 1.0 -200, 5.0 -500 and 0. 5 - 100 ug/L for dalapon, dicamba, 2, 4-D and pentachlorophenol, respectively. The detection limits were 1.0, 0. 5, 1.0 and 0. 1 ug/L, respectively. The concentration of dalapon in Nanjing Xuanwu Lake samples was detected to be 7.1 ug/L. And fortified recoveries were 102% - 105% , 96% -110% , 87% -109% for the four analytes at high, middle and low fortified levels, respectively. An easy way was also established to synthesize the N-methyl-N-nitroso-urea which was used to generate the diazomethane. The method could be used to determinate many chlorinated acid herbicides with high sensitivity, broad linear range, and minor environment pollution.