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    基质固相分散-气相色谱法-双柱双电子捕获检测器测定土壤中19种有机氯农药的含量

    Determination of 19 Organochlorine Pesticides in Soil by Gas Chromatography Coupled with Bi-columns and Bi-electron Capture Detectors with Matrix Solid Phase Dispersion

    • 摘要: 将采集的土壤样品混匀并除去混入的异物,置于冷冻干燥机中脱水后研磨混匀,封存于干燥器中备用。取此样品20.00 g,与硅藻土3.00 g和硅镁吸附剂3.00 g掺拌均匀。在加速溶剂萃取(ASE)仪的萃取池的底部铺垫硅镁吸附剂3.00 g,将上述样品混合物定量移入于此池中,于其上面铺盖一层石英砂和加盖一张滤纸片。按设定条件以体积比为1:1的二氯甲烷-正己烷混合溶液作为萃取溶剂,在90℃萃取2次。将所得萃取液合并并吹氮浓缩至体积小于1 mL,加正己烷定容至1.0 mL。此溶液作为试液进行气相色谱分析,测定其中19种有机氯农药(OCPs)的含量。色谱分析中,进样量为1.0 μL,选择HP-5 LTM和DB 1701 LTM两种极性不同的色谱柱,按程序升温条件对目标物进行分离。采用双电子捕获检测器(ECD),前ECD接在HP-5 LTM色谱柱后,后ECD接在DB 1701 LTM色谱柱后,经两种色谱柱分离,测定所制得标准曲线的线性范围均有两个相同的区段,即5~100 μg·L-1和100~1 000 μg·L-1。19种OCPs的检出限(3.143s)为0.15~0.56 μg·kg-1。如果目标物在两种色谱柱上的测定结果差异大于5倍,则判定此结果为假阳性;如差异小于5倍,则确定该化合物存在,并以数值较小者为测定结果。精密度试验测得目标物测定值的相对标准偏差(n=6)为2.7%~15%。用本方法分析了土壤标准物质(CRM818-50G),所测得19种OCPs的结果均在认定值范围内。

       

      Abstract: Sample of soil was collected and mixed thoroughly. After picking out foreign matters, the soil sample was dehydrated, homogenized by grinding and sealed up to keep in a desiccator for use as analytical sample. 20.00 g of the sample were intermixed with 3.00 g of diatomite and 3.00 g of the adsorbent, Magnesol and then the sample mixture was transferred into the extraction cell upon a layer of silica-magnesium adsorbent (3.00 g) which was spread on the botton of the cell preliminarily. After spreading a layer of quartz sand and a piece of filter paper on the surface of the sample, ASE was carried out twice by the ASE extractor according to the predetermined program using a mixed solution of dichloromethane-n-hexane with the volume ratio of 1:1 as extraction solvent at 90℃. The extracts were combined and evaporated by N2-blowing to a volume less than 1 mL, and after cooling, the volume of the solution was made up to 1.0 mL with n-hexane. 19 organochlorine pesticides (OCPs) were enriched in this solution and to be determined by the gas chromatography method. A sample injection volume of 1.0 μL was adopted in the gas chromatography procedure and 2 chromatographic columns with different polarityi.e. HP-5 LTM chromatographic column and DB 1701 LTM chromatographic column, each of the chromatographic columns was connected with an electron capture detector (ECD) were used in the gas chromatography separation. Standard curves were prepared with mixed standard solution of the 19 OCPs by gas chromatography separation and determination on each of the 2 chromatographic columns, giving same linearity ranges in 2 mass concentration sections of 5-100 μg·L-1 and 100-1 000 μg·L-1. Detection limits (3.143s) found for the 19 OCPs were in the range of 0.15-0.56 μg·kg-1. If the difference between results determined by the 2 chromatographic columes for a same analyte came cut to be larger than 5 times, the result should be judged as "false positive"; and if the difference was less than 5 times, the analyte was determined to be existing, and the smaller one of the 2 data should be taken as the result of determination. Values of RSDs (n=6) found by precision test for the 19 OCPs were ranged from 2.7% to 15%. A CRM of soil (CRM 818-50G) was analyzed by the proposed method, results of the 19 OCPs found were all within the limited ranges of certified values.

       

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