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

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5 mL甲基叔丁基醚提取,重氮甲烷甲基衍生化30 min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 ～100 μg/L范围内与色谱峰面积呈良好的线性关系(r= 0.994 5 ～0.998 0),检出限分别为1.0、0.5、1.0、0.1 μg/L.用该法测定南京玄武湖水样中的茅草枯,其质量浓度为7.1 μg/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.

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

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-butyl ether(MtBE). The chlorinated acid herbicides were derivatized by diazomethane for 30 min. The target methyl esters were determined by capillary column gas chromatography with μ-ECD. Quantitative 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 μg/L for dalapon,dicamba,2,4-D and pentachlorophenol,respectively. The detection limits were 1.0,0.5,1.0 and 0.1 μg/L,respectively. The concentration of dalapon in Nanjing Xuanwu Lake samples was detected to be 7.1 μg/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.