Evaluation of the performance of 57 Japanese participating laboratories by two types of z-scores in proficiency test for the quantification of pesticide residues in brown rice

A proficiency test for the analysis of pesticide residues in brown rice was carried out to support upgrading in analytical skills of participant laboratories. Brown rice containing three target pesticides (etofenprox, fenitrothion, and isoprothiolane) was used as the test samples. The test samples were distributed to the 57 participants and analyzed by appropriate analytical methods chosen by each participant. It was shown that there was no significant difference among the reported values obtained by different types of analytical method. The analytical results obtained by National Metrology Institute of Japan (NMIJ) were 3 % to 10 % greater than those obtained by participants. The results reported by the participant were evaluated by using two types of z -scores, that is, one was the score based on the consensus values calculated from the analytical results of participants, and the other one was the score based on the reference values obtained by NMIJ with high reliability. Acceptable z -scores based on the consensus values and NMIJ reference values were achieved by 87 % to 89 % and 79 % to 94 % of the participants, respectively. Graphical Abstract Distribution of z and z NMIJ -scores for isoprothiolane