建立了一种新型的冷冻熔炼液-液萃取法直接提取啤酒中的 N-二甲基亚硝胺（ N-nitrosodimethylamine， NDMA），萃取液经 GC-FID 分析，双柱法定性，外标法定量。优化的前处理条件为：以二氯甲烷为萃取溶剂，啤酒样品和萃取溶剂的体积比为9：1，-19℃下冷冻16 h。结果表明：NDMA 在5~200 mg / L 范围内具有良好的线性关系（r2=0.9996）；在5、10和20 mg / L 3个加标水平下的回收率分别为84.94％、83.24％、85.14％，平行7次测定的相对标准偏差（RSD）分别为3.06％、3.19％、2.63％。与常规液-液萃取方法（需要经过蒸馏、萃取、旋蒸、氮吹4个步骤）相比，本方法稳定、可靠，且操作简单，有机溶剂消耗量少。
A simple and effective sample enrichment method of frozen zone melting liquid-liquid extraction was optimized and validated for the analysis of trace N-nitrosodimethylamine (NDMA)in beer samples. The method was based on high pressure liquid-liquid extraction with a low temperature frozen step. The 90 mL beer was placed in a container with 10 mL dichlo-romethane. After agitation,the sample was kept in a freezer for 16 h at - 19 ℃ . The organic extract was analyzed by gas chromatography with a flame ionization detector( GC-FID). The accuracy,precision,detection and quantification limits and linearity of the method were evalu-ated. The results showed that the calibration curve of NDMA was linear in the range of 5-200 mg / L with a good correlation coefficient(r 2 )of 0. 999 6. The recoveries at the spiked levels of 5,10 and 20 mg / L were 84. 94% ,83. 24% ,85. 14% with the relative standard deviations(n = 7) of 3. 06% ,3. 19% ,2. 63% ,respectively. The ordinary extraction method of N-nitrosodimethyl-amine in beer includes the four steps of low-temperature distillation,liquid-liquid extraction, rotary evaporation and nitrogen blowing concentration. With the extremely low volume of sol-vent used,the proposed extraction method proved to be easy and simple,and adequate for high-throughput analysis at low cost.
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