加速溶剂萃取-气相色谱法测定茶叶中八氯二丙醚残留量及其不确定度评估

建立了加速溶剂萃取-气相色谱(ASE-GC)法测定茶叶中八氯二丙醚残留量的方法。茶叶样品经加速溶剂萃取仪用正己烷-丙酮(1∶1,体积比)提取,经硅藻土-浓硫酸(10 g∶4.0 mL )净化,以正己烷洗脱并定容,GC-ECD检测,外标法定量。此外,对测定过程中可能引入的不确定度进行了分析和评定。结果表明:在质量浓度为0.010~0.40 mg/L范围内,峰面积与八氯二丙醚的质量浓度成良好的线性关系,相关系数r=0.999 1;八氯二丙醚的添加水平在5~30 ng/g范围内,平均回收率为90.2%,相对标准偏差(RSD)为4.7%,方法的检出限(LOD)为0.005 mg/kg;当茶叶中八氯二丙醚含量为0.053 1 mg/kg时,取置信概率为95%,包含因子k=2,则其扩展不确定度U=0.003 6 mg/kg。通过对不确定度的分析,发现影响测定结果不确定度的主要来源有回收率、测量重复性和标准溶液的配制过程。

Evaluation of uncertainty in the determination of bis- ether in tea leaves by accelerated solvent extraction technique and gas chromatography

A method has been developed for the determination of bis-(2,3,3,3-tetrachloropropyl) ether in tea leaves by accelerated solvent extraction technique(ASE) and gas chromatography(GC).The samples were extracted by accelerated solvent extraction(ASE) using hexane-acetone(1∶1,V/V) as the extraction solvent,purified with celite-sulfuric acid(10 g∶0.4 mL) using hexane as an eluent.The correlation coefficient in the concentration range at 0.010-0.40 mg/L was 0.999 1,The average recoveries of bis-(2,3,3,3-tetrachloropropyl) ether in tea at 5-30 ng/g fortification level were 90.2%,with relative standard deviations(RSD) of 4.7%.The limit of detection(LOD) of the method was 0.005 mg/kg.Uncertainties originated from the measurement of bis-(2,3,3,3-tetrachloropropyl) ether in tea leaves by ASE-GC method were analysed and evaluated.When bis-(2,3,3,3-tetrachloropropyl) ether content in tea was 0.053 1 mg/kg,the relative uncertainty(UreI) was calculated to be 0.003 6 mg/kg from the experimental data when the designed incredible probability was 95% and factor(k) was 2.The results of uncertainty analyses showed that the recovery rate,repeatability of determination and preparation process of standard solution were the key issues of the testing quality control.