Proficiency Testing for Quantification of Pesticide Residues in Treated Brown Rice Samples: Comparison of Performance of Japanese Official Multiresidue, Modified QuEChERS, and QuEChERS Methods

To support analytical skill development, testing of proficiency in pesticide residue analysis in brown rice was conducted for 86 participating Japanese laboratories. Brown rice test samples containing three target pesticides (etofenprox, fenitrothion, and thiamethoxam) were distributed to participants who were free to choose an appropriate analytical method. Reported results were evaluated using a z-score based on the consensus values calculated from the participant analytical results and a z-score based on the high-reliability reference values determined by the National Metrology Institute of Japan (NMIJ). It was found that 80-89 and 82-85% of participants achieved acceptable consensus-value-based and NMIJ-reference-value-based z-scores, respectively. More than 80% of participants reported results obtained using the Japanese official multiresidue method, solid-phase extraction technique with the Quick, Easy, Cheap, Effective, Rugged, and Safe (modified QuEChERS) method or QuEChERS method. We show that the concentrations determined by the NMIJ using these three methods combined with isotope-dilution MS having high reliability agreed well and that the method performances were comparable.