IMEP-37, determination of pesticides in grapes : interlaboratory comparison report

This report presents the results of a proficiency test exercise (PT) which focussed on the determination of pesticides in grapes in support of Regulation 396/2005/EC of the European Parliament and of the Council on maximum residue levels of pesticides in or on food and feed of plant and animal origin. Eighty-seven participants from thirty-three different countries registered to the exercise, of which eighty-one reported results. From these eighty-one participants, forty were from EU countries while forty-one were from outside the EU. The test item was a grapes sample spiked with 20 selected pesticides. The assigned values were obtained as the average of results reported by five expert laboratories having demonstrated experience in the analysis of pesticides in vegetable and fruit matrices. The standard uncertainties related to the assigned values (Uref) were calculated by combining the uncertainty of the characterisation (Uchar) with a contribution for homogeneity (Ubb) and for stability (Ust). Uchar was calculated following the ISO guide 35. Laboratory results were rated with z- and zeta (ζ-) scores in accordance with ISO 13528 and ISO 17043. The z-score compares the participant's deviation from the reference value with the standard deviation for proficiency assessment (σp) used as common quality criterion, the ζ-score states if the laboratory result agrees with the assigned value within the respective uncertainty. The standard deviation for the proficiency assessment, σp, was set by the advisory board of this PT at 25% for the 20 measured pesticides based on previous experience with similar measurands. Participants were not scored for triadimenol due to the large Uref associated to the assigned value. According to the results obtained in the frame of the IMEP-37 study, the participants performed satisfactorily for the 19 scored pesticides ranging from 81 % (carbendazim) to 97 % (azoxystrobin, penconazole, pyrimethanil) of satisfactory z-scores. When analysing the results of the group of non-EU countries separately, similar results were obtained. It can be concluded that the performance in this PT is satisfactory for the laboratories world-wide