Uncertainty Evaluation for Determination of Pyrethroid Pesticide Residues in Tobacco by Gas Chromatograph-Mass Spectrometry
According to the industry standard YC/T 405.3-2011,the uncertainty of pyrethroid pesticide residues in tobacco was evaluated by using gas chromatography-mass spectrometry.By establishing the measurement model,identifying and quantifying the sources of uncertainty during the experiment,and then synthesizing and expanding the components of uncer-tainty,the actual test results of six pesticides were finally obtained.The results showed that the main factors affecting the un-certainty were standard solution preparation and standard curve fitting,followed by measurement repeatability and sample preparation,and the recovery rate had relatively little effect on the uncertainty.With a confidence of 95%and a coverage fac-tor of k=2,the measurement results and expanded uncertainty of cypermethrin,permethrin,beta-cyhalothrin,cypermethrin,valerthrin,and deltamethrin in tobacco were(0.481 0±0.040 2),(0.466 0±0.039 7),(1.035 9±0.102 4),(1.014 7±0.101 2),(0.940 0±0.075 9),(0.949 0±0.077 0)mg·kg-1,respectively.The contribution rate of standard solution preparation to the un-certainty component of the six pesticides ranged from 40%to 60%.However,the contribution rate of sample preparation and recovery to the uncertainty component of the six pesticides was generally low,ranging from 2%to 9%.It is necessary to pre-pare the standard solution at an appropriate concentration,optimize the pre-treatment steps in the sample preparation process,improve the experimental operation ability of personnel,and maintain the instrument and measuring tool regularly to reduce uncertainty.
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