Measurement Uncertainty of Determination of Profenofos (PFF) Residues in Cucumber Evaluated by Gas Chromatography (GC)

To evaluate the measurement uncertainty of the analysis results of PFF pesticide residues in cucumber extracted by NY/T 761-2008, find out the factors that have great influence on the measurement uncertainty, the experimental operation was standardized and the accuracy of the detection results was improved. A mathematical model was established through external reference material addition to evaluate the measurement uncertainty from the used of equipment, the prepared standard working fluid, and the repeatability measurement. The results showed that residual amount of PFF was 0.45 mg/kg, and the expanded standard uncertainty was 0.04 mg/kg. There were three aspects that contributed significantly to the measurement uncertainty:The relative standard uncertainty of the purity of the reference material was 2%, the relative standard uncertainty was 2.661% that pipettes was used for six times, and the relative standard uncertainty of the fitting of the standard curve was 1.615%. Therefore, in the detection, it was recommended to purchase reference material with purity of more than 98.6%, do well in storage and period verification, reduce frequency of using pipette, and use more precise measuring device when standard working fluid was prepared. Calibration of measuring device should do regularly, and the testing instruments should be verify during the test period.