Determination of Organochlorine Pesticides and Polychlorinated Biphenyls in Grains Using Gas Chromatography with Accelerated Solvent Extraction
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摘要: 针对大米、小麦、玉米和黄豆等谷物样品中有机氯农药(OCPs)和多氯联苯(PCBs)检测的前处理过程较为复杂，消耗溶剂多，易导致部分挥发性化合物损失而影响分析的准确度，本文优化了加速溶剂萃取(ASE)提取大米、小麦、玉米和黄豆等谷物样品中OCPs和PCBs的条件，比较了凝胶渗透色谱(GPC)和固相萃取柱(SPE)两种净化方式净化样品的效果，采用气相色谱-电子捕获检测器实现了样品中17种OCPs和8种PCBs单体的系统分析。结果表明，选择二氯甲烷-丙酮混合溶剂(体积比1:1)，采用ASE萃取，同时加入弗罗里硅土在线净化，可满足样品提取需求；除了黄豆和黑豆等豆制品样品需采用GPC结合SPE的净化方法外，大米、小麦、玉米等大部分谷物样品采用SPE净化即可满足测定需求。采用弗罗里硅土SPE净化，仅用9 mL正己烷-乙酸乙酯淋洗液(体积比1:1)即可将所有目标物回收，克服了有机试剂用量大、同时使用多种试剂及试剂毒性大的问题。添加低、高两个浓度水平0.69 μg/kg和5.52 μg/kg，OCPs和PCBs单体的平均回收率为71.0%～112.0%，相对标准偏差为3.6%～16.7%(n=7)；方法检出限为0.07～0.30 μg/kg，低于国家标准方法的检出限。该方法净化效率高，操作简单，分析成本较低，适用于大批量谷物样品中多种OCPs和PCBs的快速分析。Abstract: The pollution of grains is growing worse due to the soil environment being polluted. The pre-treatment for organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) detected in samples of rice, wheat, corn and soybean is a complicated process with a large amount of solvents, easily leading to volatile compound loss and effects on the accuracy of the analysis. Therefore, choosing a suitable extraction and purification method is very important to the determination of 25 OCPs and PCBs in grains with Gas Chromatography. In this paper, the extraction and purification procedures of this method have been improved greatly by optimizing the parameters of accelerated solvent extraction (ASE) and comparing gel permeation chromatography (GPC) and solid phase extraction (SPE) are described. In addition to soy products, such as soybean and black bean samples needed to be purified by GPC and SPE, most of the rice, wheat, corn and other cereal samples are purified by SPE alone. The sample was extracted with dichloromethane and acetone (V:V=1:1) by ASE (Florisil clean up in the extraction cell), cleaned up by SPE with only 9 mL n-hexane/ethylacetate (V:V=1:1) to recover all the target compounds. The problems of using a large amount of organic reagent and the highly toxic reagent were overcome. The method detection limits of 17 OCPs and 8 PCBs ranged from 0.07 to 0.3 μg/kg, better than the index in national standard method. The average recoveries of 25 OCPs and PCBs were 71.0%-112.0% in the solutions of low and high level contents of 0.69 μg/kg and 5.52 μg/kg. The relative standard deviations (RSDs) for all the compounds were 3.6%-16.7% (n=7). It was confirmed that the method was accurate and credible through determination of spiked rice samples and other grain samples. Compared with traditional methods, this method is simple and convenient to conduct with the advantages of high efficiency, rapidity and low cost. Thereby, it is feasible for the simultaneous determination of OCPs and PCBs in different kinds of grain samples.
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表 1 不同提取溶剂提取玉米样品中油脂的质量
Table 1. The extracted mass of lipid in corn sample extracted by different solvents
提取溶剂 m/g 浓缩时间t/min 样品瓶
质量油脂加样
品瓶质量油脂
质量二氯-丙酮(体积比1:1) 50.9927 51.0449 0.0522 16 正己烷-丙酮(体积比1:1) 48.3526 48.4132 0.0606 20 乙酸乙酯 49.7050 49.7625 0.0575 25 乙腈 45.3123 50.0927 0.0418 30 
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表 2 ASE在线加弗罗里硅土净化后玉米样品中的油脂量
Table 2. The extracted mass of lipid in corn sample extracted by ASE with adding Florsil and without Florsil
ASE提取 m/g 样品瓶质量 油脂加样品瓶质量 油脂质量 在线加弗罗里硅土 48.3510 48.3884 0.0374 不加弗罗里硅土 50.2665 50.3240 0.0575
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表 3 大米基质加标的精密度、回收率和方法检出限
Table 3. Spiked recoveries and detection limits of the method for OCPs and PCBs
化合物 低浓度水平 高浓度水平 方法检出限/(μg·kg-1) 0.69 μg/kg 5.52 μg/kg 平均回收率/% RSD/% 平均回收率/% RSD/% α-HCH 87.2 9.55 85.7 6.68 0.18 六氯苯 71.0 9.28 82.8 5.90 0.14 β-HCH 96.0 7.03 89.6 3.58 0.15 γ-HCH 94.4 6.44 88.0 4.43 0.13 δ-HCH 94.6 6.21 93.9 5.46 0.13 七氯 87.4 3.65 94.4 10.5 0.07 艾氏剂 89.2 5.85 87.1 10.7 0.11 环氧七氯 94.8 5.65 97.9 5.90 0.12 反式-氯丹 94.5 9.67 85.6 9.67 0.20 顺式-氯丹 87.7 7.84 91.6 6.30 0.15 p,p′-DDE 112.0 10.8 100.0 5.98 0.26 狄氏剂 88.3 10.1 91.3 10.3 0.19 异狄氏剂 92.1 7.25 100.0 5.72 0.29 p,p′-DDD 88.2 6.09 87.5 6.16 0.12 o,p′-DDT 87.9 6.43 88.6 8.34 0.12 p,p′-DDT 87.7 13.5 93.7 7.49 0.26 灭蚁灵 92.0 5.78 87.3 5.39 0.12 PCB 15 81.3 5.69 88.9 9.58 0.30 PCB 28 92.6 9.12 86.1 5.58 0.18 PCB 52 89.5 6.48 89.3 16.3 0.13 PCB 101 87.5 9.87 85.7 7.77 0.19 PCB 118 83.1 4.10 83.6 9.43 0.07 PCB 153 85.2 9.92 87.7 16.7 0.18 PCB 138 102.0 10.4 90.4 8.60 0.23 PCB 180 96.9 8.68 93.7 8.87 0.18
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表 4 谷物样品GC-ECD部分检测结果
Table 4. Determination results of OCPs and PCBs in grains by GC-ECD
化合物名称 wB/(μg·kg-1) 玉米籽 小麦 荞麦 小米 α-HCH - - - - 六氯苯 2.49 - 1.08 - β-HCH - - - - γ-HCH - - - - p,p′-DDE - - 1.26 2.03 p,p′-DDT - - - - 替代物回收率/% 2,4,5,6-四氯间二甲苯 80.32 83.16 89.97 79.88 PCB 103 92.98 95.72 107.14 97.87 PCB 204 105.87 100.4 107.92 99.46
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