茶鲜叶中3种拟除虫菊酯农药残留量测定的不确定度分析

Uncertainty evaluation for the determination of three pyrethroid pesticide residues in fresh tea leaves

目的:评定气相色谱法测定茶鲜叶中氯氰菊酯、氰戊菊酯和溴氰菊酯3种拟除虫菊酯农药残留量的不确定度。方法:通过建立数学模型,分析测定过程中的不确定度来源,包括样品测定重复性、标准曲线拟合、添加回收率、标准溶液配制、样品称量和前处理、仪器测定等,并对其进行量化、合成与扩展。结果:在0.10 mg/kg添加水平下,氯氰菊酯、氰戊菊酯、溴氰菊酯的扩展不确定度分别为0.011,0.011,0.012 mg/kg,当置信概率为95%(k=2)时,测定结果可表示为:氯氰菊酯(0.093±0.011) mg/kg,氰戊菊酯(0.094±0.011) mg/kg,溴氰菊酯(0.098±0.012) mg/kg。结论:该方法主要不确定来源为标准溶液配制、标准曲线拟合及回收率,提示样品检测过程中需对这几个方面进行严格控制。

Objective:The uncertainty of determination of three pyrethroid pesticides(cypermethrin,fenvalerate and deltamethrin) in fresh tea leaves by gas chromatography was evaluated.Methods:A mathematical model was established according to the determination process of the experiment,and the uncertainties caused by various factors in the model were identified.The sources are mainly the following 7 aspects:repeated determination of samples,fitness of standard curve,recovery rate,standard solution preparation,sample weighing and pretreatment,and the measurement of instrument.Results:At the spiking level of 0.10 mg/kg,the expanded uncertainty of measured values of cypermethrin,fenvalerate,and deltamethrin were 0.011,0.011 and 0.012 mg/kg,respectively.The detection results of three pesticides in fresh tea leaves in 95% confidence interval could be expressed as cypermethrin:(0.093±0.011) mg/kg,fenvalerate:(0.094±0.011) mg/kg,deltamethrin:(0.098±0.012) mg/kg(k=2).Conclusion:The uncertainties of the method were mainly introduced by standard solution preparation,calibration curve fitting and recovery rate,indicating that these aspects should be controlled strictly in the following sample analysis.