Evaluating the uncertainty of measurement of pesticide residue detection—a case study of four pesticide residues in strawberry by GB 23200.8—2016

Since “CNAS-GL006 guidelines of uncertainty in chemical analysis” was published in 2018, the demand for calculation method of uncertainty has been increasing. According to "GB 23200.8—2016 determination of 500 pesticides and related chemical residues in fruits and vegetables by gas chromatography-mass spectrometry", the uncertainties of profenofos, phosmet, quintozene and cyhalothrin residues in strawberries were evaluated by gas chromatography-mass spectrometry (GC-MS) combined with internal standard quantitative method. Five B-type evaluation components, including standard purity, stocking solution, working solution, sample weighing and pretreatment process, and three A-type evaluation components, including standard solution peak area, sample solution peak area and recovery, were studied. Results showed that the relative combined standard uncertainties of profenofos, phosmet, quintozene and cyhalothrin at the spiking level of 0.08 mg/kg were 3.55%, 3.22%, 2.20% and 3.66%, respectively. Two A-type evaluation components of sample solution peak area and recovery had great contribution in the combined uncertainty of four pesticide residues, which was higher than 60% for profenofos, phosmet and cyhalothrin, and higher than 31% for quintozene. In this study, the detection results of four insecticides in strawberry samples in 95% confidence interval could be expressed as profenofos: 0.085 ± 0.006 mg/kg, phosphorus: 0.084 ± 0.005 mg/kg, quintozin: 0.079 ± 0.003 mg/kg, and cyhalothrin: 0.082 ± 0.006 mg/kg (k = 2). The uncertainty assessment results will minimize the possible disputes in the judging of the residue values near the maximum residue limts.