Comparison of Assigned Values from Participants' Results, Spiked Concentrations of Test Samples, and Isotope Dilution Mass Spectrometric Results in Proficiency Testing for Pesticide Residue Analysis.

The Hatano Research Institute (HRI) at the Food and Drug Safety Center has recently organized a series of proficiency-testing (PT) programs called the "External Quality Control for Food Hygiene" in order to evaluate the analytical capability of testing laboratories that inspect food samples in accordance with the Food Sanitation Act. In one of these programs, Pesticide I, consensus values calculated from the participants' analytical results were used as assigned values, and the spiked concentrations of the prepared test samples were used for evaluating variation among individual participants. In the present study, the values obtained in the 2013-2015 rounds have been assessed by comparing the analytical results of the target pesticides obtained by using two different isotope-dilution MS (IDMS) methods. These two IDMS methods are based on a combination of different pretreatment protocols and different GC separation columns. The weighted means of the observed analytical results were higher than the corresponding assigned values, but showed good agreement with the spiked concentrations. These results indicate that the spiking concentrations of the test sample from HRI are reliable, and therefore, these values can be used to evaluate the trueness of the participants' analytical method.